New Studio Build

Hello, I'm just starting out on my second studio build, the last one was about 7 years ago and I had a lot of good help from this forum. Unfortunately I seem to have lost my account details so I've created a new account. I had to move from my last property where my studio was in the basement. The new studio I'm building is part of the extension so should be a lot easier in terms of ventilation and damp issues! At present the builds have built the shell of my office/studio. It has a concrete block and beam floor and the walls are concrete cavity with celotex in the cavity to meet building regs, this does not fill the whole of the cavity. The room is 6000mm length x 3830mm wide x 2400mm high I didn't have 100% control over the dimensions and I might be able to squeeze a little more on the height to try and swallow up some of the looses made by soundbloc layes and resilient bars (if I use them). At this stage I'm thinking through the weak points. I have limited budget to spend past making this a normal room so my plans are do just do the best I can. Because this room will also be my office and a spare room when needed it needs windows. One window as a means of egress is a need for building regulations anyway. I have order triple glazed windows but I'm expecting to secondary glaze the internal stud wall. I'll get to this later on in the post. From experience a studwall with 2 layers of 15mm soundbloc and 50mm dense acoustic slab rockwool in the studwork is very effective, I will acoustic silicone all the joins and have it skimmed. Last time I used sway braces to hold the top of the studwork but I will be looking to see if there is a cheaper alternative, I'm open to suggestions? The door opening will have 2 x 60 minute firedoors with the internal door having an additional layer of plywood attached to it, I forget what thickness I used last time but will read this forum to make sure I get this correct. I also used magnetic strip and P shaped rubber seal on both doors with strong fire door closers. I'll do this again. I'm just getting my head around sketchup so I don't have drawings yet. I have made some rough amendments to the plans for the extension so you can see how I'm thinking of putting my double door in the internal studwork. Not sure if I need a double stud internally but then the door into the breakfast room/kitchen is only a normal 1920s door (possible a modern FD30 version if the building officer says we have to). Eitherway it won't be a great soundproofing barrier. The studio will have a hipped composite slate roof and the build is single storey. This, in my mind, is the weakest point in terms of sound leakage. If I have a ceiling compromised of 2 layers of 15mm soundbloc and then 100mm dense rockwool slab that's all that will be between the room and the slate roof. What I'm thinking is that it would be wise to put at least a layer of soundbloc on top of the collars (ceiling joists) and maybe even a layer of 18mm T&G chipboard flooring (glued). This would increase the density of the ceiling considerably. I'll need to check the timbers used can support this load but I imagine they should be ok. Is there much to be gained from using resilient bars with the ceiling baring in mind there is no room above the studio? You can see from the plans that on one corner contacts the rest of the house. The main aim here is to minimise sound leakage to neighbours. If I want to record a drummer or loud electric guitar part late I don't want to upset neighbours. The house is detached and the neighbours house is about 3 meters away. Another weak point is I have to have radiators from the main house (in red on the plan). The pipe work will all be run in the screed and the pipes will come up inside the studwork. Hopefully this won't allow too much sound to travel into the main house? I plan to have all electrics enter the studwork in one place via a conduit and then surface mount them. So my main question at present are: What's the best way to approach the ceiling, how many layers should I try and get on top of the ceiling joists, I don't want to loose much of my 2400mm head height by adding room side. Are resilient bars going to provide much gain if there is no room above? Will they help prevent sound travelling into the roof space and therefore outside? Is having central heating from the main house too much of a compromise if the pipes are in the concrete screed and come up inside the studio studwork? I will be building a passive ventilation system in but I haven't researched that yet. Last time I had heated AC and built a S shaped tunnel to deaden sound so I'm familiar with some of the concepts. Thanks for any help. More invovled drawings to come. By the way do the dimensions look resonable? I've looked at some of the 'Golden ratios' and it looks close to H= 1.00 W= 1.60 L= 2.33 H = 2400 W 3830 L = 6000 (should be 5592 which it will be close to where the doors are. I plan to build a screen (in green) to put in front of drums and guitar amps which I'll sit in the back corner) I've put a rough mix position in and proposed sofa position, these could change. Thanks again Ricky

Is there any reason I'm not getting a reply, have I missed any of the forum rules? Unfortunately time is ticking on the build and I'm being pushed for some decision on the roof make up of the studio. Any help will be gratefully received. Thanks

Hi Rick, and Welcome! :) Not sure what happened here, but your thread seems to have fallen into a black hole! Sorry about that...

Unfortunately I seem to have lost my account details so I've created a new account.

If you recall the e-mail address that you registered with back then, or the thread title, or your user name, then I can search for those and re-activate your account for you. PM me.

It has a concrete block and beam floor and the walls are concrete cavity with celotex in the cavity to meet building regs,

Sounds like a good start!

Because this room will also be my office and a spare room when needed it needs windows.

Not a problem, probably. As long as you don't need to open the windows....

One window as a means of egress is a need for building regulations anyway.

Ooops! So that pair of windows DOES need to open! That is a potential problem.

I have order triple glazed windows but I'm expecting to secondary glaze the internal stud wall. I'll get to this later on in the post.

Triple glazing, plus at least one other? Sounds like a four-leaf system to me! :ahh:

50mm dense acoustic slab rockwool in the studwork is very effective,

As long as it isn't TOO dense! If you use mineral wool with very high density, that won't work well for low frequency absorption. Optimal density for mineral wool in this application is around 50 kgm3.

Last time I used sway braces to hold the top of the studwork but I will be looking to see if there is a cheaper alternative, I'm open to suggestions?

Yep, there sure is! Just attach your inner-leaf ceiling to your inner-leaf walls, and you are done! :) No sway bracing, RSIC clips, hat channel or anything else needed. As long as your walls are built with sufficient integrity, mainly in sheer, there's no problem.

The door opening will have 2 x 60 minute firedoors with the internal door having an additional layer of plywood attached to it, I forget what thickness I used last time but will read this forum to make sure I get this correct. I also used magnetic strip and P shaped rubber seal on both doors with strong fire door closers. I'll do this again.

:thu:

I have made some rough amendments to the plans for the extension so you can see how I'm thinking of

Why do you have that sort of lobby space at the top of the top left of the diagram? Is that going to be a vocal booth? Storage? Something else? Unless you REALLY need that, it would be better to get rid of it.

the door into the breakfast room/kitchen is only a normal 1920s door

I would replace that with a solid wood door. It's part of your outer leaf, so it0s a key pat of your entire isolation system. If that door is low mass, or not sealed, then your overall isolation will be rather poor.

If I have a ceiling compromised of 2 layers of 15mm soundbloc and then 100mm dense rockwool slab that's all that will be between the room and the slate roof.

This sounds like it might be one of those situations where a 3-leaf system is the best solution...

What's the best way to approach the ceiling, how many layers should I try and get on top of the ceiling joists, I don't want to loose much of my 2400mm head height by adding room side.

Please take photos or draw an accurate diagram of the roof trusses, and how they fit in with the outer-leaf walls of the room itself.

Are resilient bars going to provide much gain if there is no room above?

You probably wont need that, if you build the ceiling correctly.

Is having central heating from the main house too much of a compromise if the pipes are in the concrete screed and come up inside the studio studwork?

It would be best to avoid that, if possible, and assuming you need good isolation from the rest of the house. I doubt that you will need that anyway, once you get your HVAC system installed and running. Get one that provides both heating and cooling, and you will have all of your bases covered.

By the way do the dimensions look resonable?

Have you checked in detail? Use one of these Room Ratio calculators to figure out the best dimensions for your room: http://www.bobgolds.com/Mode/RoomModes.htm http://amroc.andymel.eu/ Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful to help figure out the best dimensions.

I've put a rough mix position in and proposed sofa position, these could change

The mix position and speaker positions will HAVE to change! The ones shown in your diagram are pretty bad.... :) - Stuart -

Hi Stuart, Thanks very much for your reply, not sure how my post vanished but glad you found it. I'm still at a stage of building you can be lots of help :)

One window as a means of egress is a need for building regulations anyway. Ooops! So that pair of windows DOES need to open! That is a potential problem.

yup, I have to have at least one opening window I can climb out of in case of fire, The room is next door to the kitchen/breakfast room so more chance of this! As mentioned I've spec'd triple glazed UPVC window in the outer leaf. Can you recommend any resources on building an internal sliding window that would have decent sound reduction properties or am I best to order another UPVC inward opening window with thicker glass? I built a studio in a basement about 7 years ago and had a light well which was also my means of egress. Here I had a normal Velux type window on top of the light well and then an inward opening UPVC window with 2 sheets of glass of different thicknesses. Can't remember what thickness but one was pretty thick. This solution worked really well but the studio was underground and the light well was a meter long and only just big enough for me to crawl out. The window in the new studio is a much bigger area. The tricky area is around the window opening. The triple glazed window sits in the outer leaf and I need and opening on the inner leaf. What I did last time was to run a rubber strip around the window on the outer leaf and then plasterboard reveals into the rubber strip, 3 layers. This provided some decoupling of inner and outer while closing off the cavity. This time I would then put another window on the inner leaf. Is there a better way to do the reveal/cheeks around the window?

As long as it isn't TOO dense! If you use mineral wool with very high density, that won't work well for low frequency absorption. Optimal density for mineral wool in this application is around 50 kgm3.

yes it is :) How much do you recommend putting in the ceiling, is 50mm enough? Also if I build the inner leaf support out of timber joists that alternate with the main roof structure does the rockwool just get packed between the timbers or lay above? I assume it doesn't matter that the rockwool connects the inner and out leaf because it doesn't transmit sound if it's not over compressed?

Yep, there sure is! Just attach your inner-leaf ceiling to your inner-leaf walls, and you are done! :) No sway bracing, RSIC clips, hat channel or anything else needed. As long as your walls are built with sufficient integrity, mainly in sheer, there's no problem.

Great news, I have Rod Gervais' book and there is a detail of this type of structure. I'm assuming the diagonal braces aren't necessary if the Timber is thick enough? I'll definitely look at the fire stop section as this sounds important. I've attached some pictures of the structure of the joists in my ceiling. The only issue is how the ends have been constructed. Because I've only just read this I haven't told the carpenter I want to build the inner ceiling structure attached to my inner leaf walls. Do you think I'll be ok constructing the inner leaf ceiling structure as far a long as I can and getting the carpenter to construct what he can for the last 500mm or so on each end without connecting to the outer leaf? Is this an area I need a structural engineer to calculate load or is 3 leafs of soundbloc plasterboard not too much? You can see the end structures would prevent the inner leaf ceiling joists sitting between the outer leaf timbers? The piece of timber you see underneath is not part of the final structure and will be removed. One solution the carpenter suggested to prevent him having to rebuild the ends, which is an option, was to build the ends of the studwork walls a bit shorted so the end of the soundbloc ceiling could sit on top of the studwork. This might make boarding the ceiling a little tricky but I can't see an issue in terms of soundproofing. I've looked into this further with the carpenter since posting the paragraph above. What we can do is build the studwork and ceiling structure first, leaving the ends off. Then plasterboard the ceiling and build the end studwork underneath where the plasterboard goes over the end ceiling joists to support it from underneath. Hope that makes sense? It means it will still be supported at 400mm centres while keeping the inner leaf separate from the outer leaf. Is there a calculation for what size timbers to use for the ceiling joists if I'm using a 3 leaf 15mm soundbloc ceiling? That's a lot of weight! Also should the studwork still be 4x2" timber at 400mm centers or do I need to add a layer of structural plywood or diagonal bracing to take the load of the ceiling through the Studwork? I've also talked with my structural engineer since this post. He did some calculations and c24 2x8 timbers are easily man enough to support 3 layers of 15mm sounbloc board at 400mm centres with a 4m room span. There's a lot of allowance for dead and live load above which I'll never need as my roof space is unusable. He also said 2x4 timbers at 400 centres is plenty for the walls over then dimensions of my room. We just need to double up the wall plate for the ceiling timbers. I might add some noggins and diagonal bracing straps anyway. Does building a room within in a room like this necessitate some form of ventilation between the outer masonry double cavity wall and in the inner studwork? The block and beam floor will have 100mm Celotex on it before the screed is poured so the floor is insulated. The outer masonry cavity wall has 50mm Celotex in it and the studwork will have acoustic rockwool slab which also acts as a thermal insulator. I'm just concerned I'm making an unventilated chamber behind my studwalls and if vapour travels through the inner leaf it has no where to go, especially if I create the fire stop at the top of the cavity (as recommended in the book), am I over thinking this?!

Why do you have that sort of lobby space at the top of the top left of the diagram? Is that going to be a vocal booth? Storage? Something else? Unless you REALLY need that, it would be better to get rid of it.

The lobby space was intended to prevent me having to make an ugly door off the breakfast room. We ahve a period 1920s house and we don't want a fire door with a fire door closer on the top off that room. The plan was to have a normal 1920s (or I can get a 60 minute fire door repro 1920s style door with plywood on the back) off the breakfast room. Then I enter the lobby which has a door through the inner leaf with a fire door closer on, rubber seals and magnetic strips. I see what you mean about compromising the outer leaf. Maybe the 60 minute repro door with plywood on the back is the best route. Are there any fire door closers that I could use that you can't see from the outer side. The door would have to open into the breakfast room so the door closer would need to be on that side. When I looked last time the door closers that fit in the frame didn't pull the door onto the rubber seals enough? The lobby was also going to be where I put my soundproof ducting boxes for my proposed fresh air system. I'm not going to be able to access the roof space really so hidding stuff up there isn't an option, especially if I don't have the lobby as I'd have to cut a hatch in the ceiling, bad!

It would be best to avoid that, if possible, and assuming you need good isolation from the rest of the house. I doubt that you will need that anyway, once you get your HVAC system installed and running. Get one that provides both heating and cooling, and you will have all of your bases covered.

That a shame, I'm not a fan of AC. I find it really affects my sinues and vocals. I also have to work in here for my day job and I don't really like the idea of having to sit in heated AC all winter. I've been loving working at home instead of the office because that's what they have. That said I'll look into cost. Last time I used HVAC and it was pretty expensive to buy and install. Is having pipes through the screed floor connected to the rest of the house going to be terrible? The other option is I could have electric underfloor heating in there. I plan to decouple the floor from the room next door by putting a rubber strip at the threshold so the Celotex insulation isn't connected and the screed isn't connected. I live in the UK and apart for 3-4 weeks when we might have some hot weather it doesn't really get that hot, we are having a heatwave at the moment though! :)

Have you checked in detail? Use one of these Room Ratio calculators to figure out the best dimensions for your room: http://www.bobgolds.com/Mode/RoomModes.htm http://amroc.andymel.eu/ Both of those are very good, and will help you to decide how best to build your room. They give you tons of information that is really useful to help figure out the best dimensions.

I will do this later. I'm sort of stuck with the dimensions so I was just interested. Last time I looked the ratios looked pretty good.

The mix position and speaker positions will HAVE to change! The ones shown in your diagram are pretty bad.... :)

What's so bad? I thought it was good to have the longer length of the rectangle behind your mix position? I appreciate the monitors are the correct distance from the back wall. Just a rough placement. Is it better to have the shorter distance behind the mix position then? I can't achieve perfection here because it's my office, home and I don't have endless finances. I've produced commercial grade mixes in some terrible rooms so I'm just hoping to produce the best I can and make a nice space to be in for writing and rehearsing without upsetting my neighbours if it's late :) Here are the room size calcs. I'd appreciate some help understanding these? Freq % Wavelength, 1/2, 1/4 p,q,r Mode Group Weighting 28.7 hz 12 : 6 : 3 (1,0,0 Axial) Start iso, End iso 45.0 hz 36.2% 7.65 : 3.83 : 1.91 (0,1,0 Axial) Start iso, End iso 53.3 hz 15.5% 6.46 : 3.23 : 1.62 (1,1,0 Tangential) Start iso 57.4 hz 7.1% 6 : 3 : 1.5 (2,0,0 Axial) End iso 71.8 hz 20% 4.8 : 2.4 : 1.2 (0,0,1 Axial) 72.9 hz 1.5% 4.72 : 2.36 : 1.18 (2,1,0 Tangential) Start iso 77.3 hz 5.6% 4.46 : 2.23 : 1.11 (1,0,1 Tangential) 84.7 hz 8.7% 4.07 : 2.03 : 1.02 (0,1,1 Tangential) 86.1 hz 1.6% 4 : 2 : 1 (3,0,0 Axial) 89.4 hz 3.6% 3.85 : 1.93 : 0.96 (1,1,1 Oblique) 89.9 hz 0.5% 3.83 : 1.92 : 0.96 (0,2,0 Axial) 91.9 hz 2.1% 3.75 : 1.87 : 0.94 (2,0,1 Tangential) 94.4 hz 2.6% 3.65 : 1.82 : 0.91 (1,2,0 Tangential) 97.1 hz 2.7% 3.55 : 1.77 : 0.89 (3,1,0 Tangential) Near 102.3 hz 5% 3.37 : 1.68 : 0.84 (2,1,1 Oblique) 106.7 hz 4.1% 3.23 : 1.61 : 0.81 (2,2,0 Tangential) 112.1 hz 4.8% 3.07 : 1.54 : 0.77 (3,0,1 Tangential) 114.8 hz 2.3% 3 : 1.5 : 0.75 (4,0,0 Axial) 115.0 hz 0.1% 2.99 : 1.5 : 0.75 (0,2,1 Tangential) 118.6 hz 3% 2.9 : 1.45 : 0.73 (1,2,1 Oblique) 120.8 hz 1.8% 2.85 : 1.43 : 0.71 (3,1,1 Oblique) 123.3 hz 2% 2.79 : 1.4 : 0.7 (4,1,0 Tangential) 124.5 hz 0.9% 2.77 : 1.38 : 0.69 (3,2,0 Tangential) 128.6 hz 3.1% 2.68 : 1.34 : 0.67 (2,2,1 Oblique) 134.9 hz 4.6% 2.55 : 1.28 : 0.64 (0,3,0 Axial) 135.4 hz 0.3% 2.54 : 1.27 : 0.64 (4,0,1 Tangential) 137.9 hz 1.8% 2.5 : 1.25 : 0.62 (1,3,0 Tangential) 142.7 hz 3.3% 2.41 : 1.21 : 0.6 (4,1,1 Oblique) 143.5 hz 0.5% 2.4 : 1.2 : 0.6 (0,0,2 Axial) 143.5 hz 0% 2.4 : 1.2 : 0.6 (5,0,0 Axial) 143.7 hz 0.1% 2.4 : 1.2 : 0.6 (3,2,1 Oblique) 145.8 hz 1.4% 2.36 : 1.18 : 0.59 (4,2,0 Tangential) 146.4 hz 0.4% 2.35 : 1.18 : 0.59 (1,0,2 Tangential) 146.6 hz 0.1% 2.35 : 1.17 : 0.59 (2,3,0 Tangential) 150.4 hz 2.5% 2.29 : 1.15 : 0.57 (0,1,2 Tangential) 150.4 hz 0% 2.29 : 1.15 : 0.57 (5,1,0 Tangential) 152.8 hz 1.5% 2.25 : 1.13 : 0.56 (0,3,1 Tangential) 153.1 hz 0.1% 2.25 : 1.12 : 0.56 (1,1,2 Oblique) 154.6 hz 0.9% 2.23 : 1.11 : 0.56 (2,0,2 Tangential) 155.5 hz 0.5% 2.21 : 1.11 : 0.55 (1,3,1 Oblique) 160.0 hz 2.8% 2.15 : 1.08 : 0.54 (3,3,0 Tangential) 160.4 hz 0.2% 2.15 : 1.07 : 0.54 (5,0,1 Tangential) 161.0 hz 0.3% 2.14 : 1.07 : 0.53 (2,1,2 Oblique) 162.5 hz 0.9% 2.12 : 1.06 : 0.53 (4,2,1 Oblique) 163.2 hz 0.4% 2.11 : 1.06 : 0.53 (2,3,1 Oblique) 166.6 hz 2% 2.07 : 1.03 : 0.52 (5,1,1 Oblique) 167.4 hz 0.4% 2.06 : 1.03 : 0.51 (3,0,2 Tangential) 169.4 hz 1.1% 2.03 : 1.02 : 0.51 (0,2,2 Tangential) 169.4 hz 0% 2.03 : 1.02 : 0.51 (5,2,0 Tangential) 171.8 hz 1.3% 2 : 1 : 0.5 (1,2,2 Oblique) 172.2 hz 0.2% 2 : 1 : 0.5 (6,0,0 Axial) 173.3 hz 0.6% 1.99 : 0.99 : 0.5 (3,1,2 Oblique) 175.4 hz 1.1% 1.96 : 0.98 : 0.49 (3,3,1 Oblique) 177.1 hz 0.9% 1.94 : 0.97 : 0.49 (4,3,0 Tangential) 178.0 hz 0.5% 1.93 : 0.97 : 0.48 (6,1,0 Tangential) 178.8 hz 0.4% 1.93 : 0.96 : 0.48 (2,2,2 Oblique) 179.9 hz 0.6% 1.91 : 0.96 : 0.48 (0,4,0 Axial) 182.1 hz 1.2% 1.89 : 0.95 : 0.47 (1,4,0 Tangential) 183.8 hz 0.9% 1.87 : 0.94 : 0.47 (4,0,2 Tangential) 183.9 hz 0% 1.87 : 0.94 : 0.47 (5,2,1 Oblique) 186.6 hz 1.4% 1.85 : 0.92 : 0.46 (6,0,1 Tangential) 188.8 hz 1.1% 1.82 : 0.91 : 0.46 (2,4,0 Tangential) 189.2 hz 0.2% 1.82 : 0.91 : 0.46 (4,1,2 Oblique) 190.0 hz 0.4% 1.81 : 0.91 : 0.45 (3,2,2 Oblique) 191.1 hz 0.5% 1.8 : 0.9 : 0.45 (4,3,1 Oblique) 191.9 hz 0.4% 1.79 : 0.9 : 0.45 (6,1,1 Oblique) 193.6 hz 0.8% 1.78 : 0.89 : 0.44 (0,4,1 Tangential) 194.3 hz 0.3% 1.77 : 0.89 : 0.44 (6,2,0 Tangential) 195.8 hz 0.7% 1.76 : 0.88 : 0.44 (1,4,1 Oblique) 197.0 hz 0.6% 1.75 : 0.87 : 0.44 (0,3,2 Tangential) 197.0 hz 0% 1.75 : 0.87 : 0.44 (5,3,0 Tangential) 199.0 hz 1% 1.73 : 0.87 : 0.43 (1,3,2 Oblique) 199.4 hz 0.2% 1.73 : 0.86 : 0.43 (3,4,0 Tangential) 200.9 hz 0.7% 1.71 : 0.86 : 0.43 (7,0,0 Axial) 202.0 hz 0.5% 1.71 : 0.85 : 0.43 (2,4,1 Oblique) 203.0 hz 0.4% 1.7 : 0.85 : 0.42 (5,0,2 Tangential) 204.6 hz 0.7% 1.68 : 0.84 : 0.42 (4,2,2 Oblique) Thanks for your help

Morning Stuart, Has my post disappeared into the abyss again :? ? Any responses would be really helpful as I need to make some decision soon because the rest of the extension is moving on and the builders need to know how I want to move ahead with things like the heating and ventilation. Thanks

not sure how my post vanished but glad you found it.

It didn't really "vanish": I just happened to miss it, and it seems nobody else noticed it either!

As mentioned I've spec'd triple glazed UPVC window in the outer leaf.

I'm not sure if you are aware of this, but triple-leaf barriers are pretty lousy acoustically. Here's why: That's for a wall, but the same applies to windows. The one on the left shows how much isolation you'd get from a 4-leaf wall, consisting of two stud frames with drywall on both sides of each frame. The second one shows what would happen if you take one sheet of drywall out of that system, making it 3-leaf: You get a whopping jump of nearly 10 points in isolation. And the one on the right shows what would happen if you take out the other internal leaf and use that to beef up the outside leaves, making it just two leaf: Another whopping ten point jump. Compare the left one to the right one: They both have the exact same materials, the same total weight, the same total thickness, but the 2-leaf is one hundred times better at blocking sound.

Can you recommend any resources on building an internal sliding window that would have decent sound reduction properties or am I best to order another UPVC inward opening window with thicker glass?

Just use a pair of ordinary wood-framed sliding windows with a single pane of thick laminated glass in each. One window goes in the outer-leaf, the other in the inner-leaf. As long as the frame is fairly massive and has really good seals, that will give you decent isolation.

Is there a better way to do the reveal/cheeks around the window?

Here's a sequence of photos that shows how one of my customers in Australia did it. In this case, he built the windows on-site, using my design of window frame, but you could do roughly the same thing with pre-built sliding glass window units:

How much do you recommend putting in the ceiling, is 50mm enough?

As much as you can get in without compressing it, and as much as you can afford! But at least 10cm.

Also if I build the inner leaf support out of timber joists that alternate with the main roof structure does the rockwool just get packed between the timbers or lay above?

Fill each empty "bay" between joists individually, side to side, front to back, top to bottom.

I assume it doesn't matter that the rockwool connects the inner and out leaf because it doesn't transmit sound if it's not over compressed?

:thu: right.

I'm assuming the diagonal braces aren't necessary if the Timber is thick enough?

You will still need some type of cross-bracing, probably. I usually put "noggins" across between adjacent joists at least every 24", simply to have nailing surfaces behind drywall joints. Those noggins also help to keep the joists straight and true, with no warping, twisting, etc.

The only issue is how the ends have been constructed.

I would get that fixed if that were my place. You want to have completely flat ceiling across the entire span of the room, since that is going to be your middle-leaf ceiling, so whatever you can do to make that happen easily would be a good idea.

... inner leaf support out of timber joists that alternate with the main roof structure ...

If you build an "inside-out" ceiling, you don't need to do that. Your acoustic ceiling would be higher like that, and better damped, more diffuse.

Is there a calculation for what size timbers to use for the ceiling joists if I'm using a 3 leaf 15mm soundbloc ceiling?

Yes. There are span tables and span calculators on-line, but those might not meet your local code requirements, so it's best to check with a locally certified structural engineer or building inspector to see what is required by YOUR code.

Also should the studwork still be 4x2" timber at 400mm centers or do I need to add a layer of structural plywood or diagonal bracing to take the load of the ceiling through the Studwork?

Are we talking about the ceiling here? If so, the framing is likely going to be much bigger than 2x4. Probably 2x6 or even 2x8. Once again your span tables / structural engineer will tell you.

2x4 timbers at 400 centres is plenty for the walls over then dimensions of my room.

Right. You only need larger studs if you have ceilings over about 12 feet, or other unusual needs.

We just need to double up the wall plate for the ceiling timbers.

Double top plate is pretty much a standard in most building codes that I'm aware of.

do I need to add a layer of structural plywood ...

I pretty much always do the walls and ceiling as one layer of thick OSB direct on the studs, then a layer of thick drywall on top of that, possibly with Green Glue damping compound in between if that is needed. That provides excellent sheer strength and rigidity to the wall, and also provides a 100% nailing surface across the entire wall.

I might add some noggins

You HAVE to have noggins! You do need them at least every 48" and preferably every 24".

Does building a room within in a room like this necessitate some form of ventilation between the outer masonry double cavity wall and in the inner studwork?

No. Doing that would trash your isolation. No ventilation at all. It is critical to seal both leaves absolutely air-tight. Even a tiny crack can degrade your isolation. If air can get through, then so can sound: after all, sound is just vibrations in the the air, so if there's an air connection through a leaf, then there is also a sound connection. What you do need to do is to seal the wall surface with a good quality masonry sealant, or plaster, or paint, or all three of those: Concrete block is vary porous, and that surface has to be sealed air-tight.

I'm just concerned I'm making an unventilated chamber behind my studwalls and if vapour travels through the inner leaf it has no where to go,

That's why you put a vapor barrier on there! :) That's a standard part of building any cavity wall. There's a water barrier on the outside of the outer leaf, which is often Tyvek on stud framed walls, or sealant / stucco / plaster / paint on masonry walls, then there's a vapor barrier somewhere inside the cavity, tight up against the warmer surface, which is usually the inner-leaf. The water barrier allows the wall to breathe while keeping liquid water out, and the vapor barrier controls air diffusion into the cavity from inside the room. Sort of. It's often more complicated than that, and varies from place to place, depending on climate and building materials, but that's the general idea. So you will almost certainly need a vapor barrier on the side of your inner-leaf that faces the cavity.

Are there any fire door closers that I could use that you can't see from the outer side.

There are, yes. Some types of door closer are meant to be used on the "push" side of the door, not the "pull" side. There are many types, for many situations. There are even some types that can be completely hidden inside the door framing, but I'm not sure if those are able to handle the huge weight of studio doors.

That a shame, I'm not a fan of AC. I find it really affects my sinues and vocals. I also have to work in here for my day job and I don't really like the idea of having to sit in heated AC all winter.

For a studio, the air conditioner will likely be in cooling mode most of the time, not heating mode. The studio is double-sealed with two very high mass walls (which means high thermal mass too), two complete hermetic barriers, and very, very thick insulation all around. The heat generate inside is not going anywhere, and needs to be removed. You might need to have your system in heat mode occasionally, just to get the room warmed up, but after that it will need to be in either cooling mode or just dehumidification mode. There is no reason at all why a properly designed, properly dimensioned, properly installed, properly used HVAC system would affect your health. On the contrary, it should protect your health! It should keep the humidity constant at around 40-50%, and it should keep the temperature constant, at around 19-22°c. Those are the conditions that are optimal for musical instruments, microphones, electronic gear, ... and people. There will also be a constant flow of fresh air into the room, and removal of the same amount of stale air, at the correct rate and correct speed for the dimensions of the room, and for the room occupancy. If you DON'T have a proper system, then the temperature and humidity will be uncontrolled and swing wildly from extreme to extreme, and in that case, your health would likely suffer. As would your instruments, mics and gear.

Is having pipes through the screed floor connected to the rest of the house going to be terrible?

Please explain how those pipes would manage to control the humidity in the room, and the air flow rate and speed, and the volume of fresh air ... :)

The other option is I could have electric underfloor heating in there.

Please explain how that electric underfloor heating would manage to control the humidity in the room, a and the air flow rate and speed, and the volume of fresh air ... :)

I live in the UK and apart for 3-4 weeks when we might have some hot weather it doesn't really get that hot,

Have you ever spent a lot of time in a small room that is fully sealed, absolutely hermetically, twice over, contained within two very high thermal mass walls, and very large thicknesses of thermal isolation, with several hundred watts of heat-emitting objects in the room, plus a humidity emitting object, no fresh air flow, no dehumidification? Lack of heat is not the problem! Too much heat is the problem. Along with too much humidity, and no way of getting rid of it. Every single breath you exhale is about 5 to 6% water vapor. About 0.03 grams of water. So ten breaths is .3 grams, and 30 breaths is 1 gram of water that went into the room air. Put another way, the relative humidity of the air you exhale is roughly 100%. If there's nothing in the room that is removing that, take a guess what happens? :) Heat is not the only issue: Humidity is.

What's so bad? I thought it was good to have the longer length of the rectangle behind your mix position

Right, but that's just one of many factors. It's the whole arrangement of the speakers and mix position.

I appreciate the monitors are the correct distance from the back wall

Front wall. The wall where the speakers are, is at the front of the room, not the back. The front of the room is in front of you! :) The speakers and mix position need to be set up for good acoustics. Not the way you are showing. As long as you are aware of that, and plan to fix it, that's fine. - Stuart -

I'm not sure if you are aware of this, but triple-leaf barriers are pretty lousy acoustically.

School boy error! Unfortunately these are payed for and waiting to be installed. Because of budget limitations for now I'll have to have them installed in the outer leaf and then make a thick glass sliding window in the inner leaf. I'll use the photos to construct the frame and 'join' across the two leafs.

I'm assuming the diagonal braces aren't necessary if the Timber is thick enough? You will still need some type of cross-bracing, probably. I usually put "noggins" across between adjacent joists at least every 24", simply to have nailing surfaces behind drywall joints. Those noggins also help to keep the joists straight and true, with no warping, twisting, etc.

Looking at Rod's diagram I'll have to drop the height of my inner ceiling to get the diagonal ceiling joist braces in without touching the outer leaf joists. I've talked with the structural engineer and he says 2x8 C24 timbers at 400mm centres will easily take the ceiling load without warping etc. What do you think? I will be nogging out the wall joists which are 2x4 at 400mm centres.

The only issue is how the ends have been constructed. I would get that fixed if that were my place. You want to have completely flat ceiling across the entire span of the room, since that is going to be your middle-leaf ceiling, so whatever you can do to make that happen easily would be a good idea.

I've worked out a way to build the roof under the ends of the rooms and support with the end studwall from underneath. This will provide adequate support without connecting the inner and outer leaf.

Double top plate is pretty much a standard in most building codes that I'm aware of.

Correct, carpenter agrees and is doing this anyway

I pretty much always do the walls and ceiling as one layer of thick OSB direct on the studs, then a layer of thick drywall on top of that, possibly with Green Glue damping compound in between if that is needed. That provides excellent sheer strength and rigidity to the wall, and also provides a 100% nailing surface across the entire wall.

So the ceilng will be 1 layer of OSB and 2 layers of soundbloc plasterboard, the walls 1 of each?

Does building a room within in a room like this necessitate some form of ventilation between the outer masonry double cavity wall and in the inner studwork? No. Doing that would trash your isolation. No ventilation at all. It is critical to seal both leaves absolutely air-tight

I ask because I had to do this at my last studio which was in a basement that was fully underground. Even though the walls were well tanked there was still moisture in the cavity. I create 2 small airbricks at ground height that had a tube lined with air con lining foam. These provided ventilation to that space and I never heard any sound escape through the airbricks outside. There won't be anything like that moisture issue here though. I'll look around for a good masonry sealant. Oh, that studio had a vapour barrier as will this one. Because of that previous build I'm too familiar with vapour barriers and where the go! :) One thing I'm not sure of still is the outer roof is covered with composite slate tiles, these obviously air gaps. The roof void needs air to vent the timbers in there. It's not a big space and is very tight on top of the ceiling joists. Any sound that makes it's way through the inner leaf walls can travel straight into this space and through the slate tiles. What do you suggest here? I can take some more photos and will try and do a diagram at lunch and attach it. I've just added this diagram to this post, it shows a cross section. You can see the area I'm concerned about. Where the wall cavity joins the roof void. The airspace is connected here and the roof has slate effect tiles. This also has a breathable membrane under the slates but that obviously isn't going to stop any sound transfer. Roof tiles also have gaps between them making them a poor sound proofing layer. What do you recommend I do here? There is very little room between the rafters and the joists to add a layer on top of the joist. Also do you have any other diagrams for how to create the fire stop at the top of the wall cavity to prevent a flue effect behind the inner leaf? There is one in Rod's book but a little more info would be helpful? I've included the diagram from Rod Gervais' book here (I hope I'm allowed to do this?). I include it because I'm not sure what the 2 x6 Blocking is, used as a fire stop? What type of material is this? It looks like it connects the 2 leafs together? The other really important question I have based on this diagram is - Do I need the midspan bracing? My structural engineer thinks not. I'm using 2 x8 joist to suspend the ceiling soundbloc. If I use the bracing it means I have to drop the inner leaf joists more to clear the outer leaf joists which means less headroom and I'm not keen on this. I understand what bracing is for but I've also been told I don't even need a central nogin on my outer joists because they are 2 x8 timbers and the way the hip roof structure is it's stiff enough.

For a studio, the air conditioner will likely be in cooling mode most of the time, not heating mode.

I had AC on my last studio. Maybe because it was underground but it was never hot, even in the height of summer. This one will different on that front and I hear you on the humidity. I'll look into this and what size/type I need. I know there's a lot of info on this forum about it.

The speakers and mix position need to be set up for good acoustics. Not the way you are showing. As long as you are aware of that, and plan to fix it, that's fine.

Yeah I haven't worked the mix and monitor positions out at all yet. I will spend time on this later. As long as the room shape and size is reasonable. Did you get a chance to look at the calculations for the room? While I'd like it to be as good as it can be all the mixes I've had played on commercial radio over the years have been mixed in some less than ideal rooms so I'm used to working with less than perfect rooms. Thanks for all your help

Looking at Rod's diagram I'll have to drop the height of my inner ceiling to get the diagonal ceiling joist braces in without touching the outer leaf joists.

Then don't look at Rod's diagram! :) Instead, look into the concept of the "inside out" ceiling... With that, your drywall can be just a few mm below the bottom of the floor joists above you, and the framing for that ceiling would be BELOW the drywall, on the inside of the room. In other words, the joists face the room, and the drywall faces the cavity.

I've talked with the structural engineer and he says 2x8 C24 timbers at 400mm centres will easily take the ceiling load without warping etc. What do you think?

Sounds good to me, if that's what your structural guy said!

I will be nogging out the wall joists which are 2x4 at 400mm centres.

??? Not sure I follow the connection.... What's the connection between where the wall noggins go, and the dimensions of the ceiling joists? Not following you here....

I've worked out a way to build the roof under the ends of the rooms and support with the end studwall from underneath. This will provide adequate support without connecting the inner and outer leaf.

Diagram, please! Or better still, model in SketcHup!

So the ceilng will be 1 layer of OSB and 2 layers of soundbloc plasterboard, the walls 1 of each?

Why "soundbloc", specifically? sound waves cannot read the price tags on your mass. All they see is the actual mass itself, in terms of X-many kilograms per square meter. They really don't care how much you paid for each of those kilograms.... In other words, go with the cheapest mass that will get the job done. You won't impress the sound waves by buying more expensive mass! Also, why are you going with different densities on the walls vs. the ceiling?

I ask because I had to do this at my last studio which was in a basement that was fully underground. Even though the walls were well tanked there was still moisture in the cavity.

Then you had a seal problem! :) The obvious implication here is that you must absolutely ensure that you do NOT have a seal problem this time. Put the moisture barrier, air barrier, and vapor barrier in the correct locations, and seal it all properly so that you won't ever get moisture trapped in the wall cavity.

Oh, that studio had a vapour barrier as will this one

Vapor barriers do not keep your wall cavity dry: They merely control the movement of vapor through the wall. Did your other wall also have moisture barriers and air barriers? Does this one?

One thing I'm not sure of still is the outer roof is covered with composite slate tiles, these obviously air gaps. The roof void needs air to vent the timbers in there.

Right. That's unavoidable. Nothing you can do to change that.

Any sound that makes it's way through the inner leaf walls can travel straight into this space and through the slate tiles.

Right.

What do you suggest here?

If you have a vented roof deck, then you have no choice: you must go with a three-leaf system for your ceiling. The slate tiles are your outer leaf. You then need a "middle leaf" that creates the actual air-tight layer of mass for the isolation system. Ideally, that would go on top of the joists above you, leaving the depth of the joist as the air gap for your inner-leaf.

I've included the diagram from Rod Gervais' book here (I hope I'm allowed to do this?).

I don't think Rod will mind, as long as you attribute it to him! He only gets upset when people try to pass off diagrams from his books as their own work.

I include it because I'm not sure what the 2 x6 Blocking is,

It's what you would call "nogging" in Australia, or "noggins" in the UK, as far as I can tell. Just pieces of 2x6 that provide support for something else. In this case, it provides support for the 1/2" drywall that is part of the fire stop system.

What type of material is this? It looks like it connects the 2 leafs together?

It is labeled right there, as 4PSF mineral wool, compressed 25%. Don't compress it more than that! 25% is about the limit for compressing insulation. If you compress it much more than that, it can start flanking. But at 25% it is not connecting the leaves: it is still decoupled.

The other really important question I have based on this diagram is - Do I need the midspan bracing? My structural engineer thinks not.

Not sure what you mean by "midspan bracing", but if your engineer says you don't need it, then I'd probably be on his side of the argument! :) But please explain what you mean by that term: it can mean several things.

Yeah I haven't worked the mix and monitor positions out at all yet. I will spend time on this later. As long as the room shape and size is reasonable.

It's a small room, so you don't have many options for the way you can lay out the speakers and mix position. Rather limited, in fact! :) There's a theoretically optimal layout for that room, but reality can be a bit different from theory. Once you have the inner shell complete, then you can set up your speakers and chair in the "optimal" locations and run some tests using REW, then make some adjustments and test again, until you find the best arrangement. Are you planning to flush-mount ("soffit-mount") your speakers? What is the basic design concept that you plan to use for your room?

While I'd like it to be as good as it can be...

:thu: Yup! Then you are in the right place, for sure, right here on the forum. In fact, the goal should be to make it "amazing"... :) ( See my signature ... ) - Stuart -

Hi Stuart, After some hold ups on the rest of the house rennovation we're back on to the studio. We've managed to redesign the roof structure and so we've moved the collars/joists up 400mm so that the underside can be be covered in T&G 22mm moisture resistant chipboard. These will be glued together and joins covered in acoustic sealant. I then propose to paint them with PVA to seal the surfaces. We will make a continuous middle layer(as recommended) which will cover the underside of the joists and on the edges the bottom of the rafters to the wall plate. This then allows us to easily make the internal studwork with the the joists for the inner leaf ceiling supported on the wall plate of the studwalls. My only concern still is sealing the masonry walls in the way you suggested. I understand about what you're saying about concrete blocks being porous but I'm just nervous of creating a potential mould breeding ground by sealing the walls. The cavity will then have no air flow at all as there will be a vapour barrier on the studwall between the rockwool (backside) and the first layer of OSB/STerling board, which is covered with 15mm plastboard (roomside). The top of the cavity is filed with Rockwool slab. This is fire retardant so should also act as a fire stop at the top of the cavity. HAve you ever seen any mould or damp issues when sealing the back of cavity so completely? I do appreciate it's key to good soundproofing in principle, it just seems to go against good building practice? My other question is do you feel 22mm T&G chipboard is enough for the middle layer. The out layer is concrete, slate effect tile so doesn't really do a lot when it comes to soundproofing. I have to fit 300mm RW45 Rockwool slab between my inner leaf and middle leaf (chipboard T&G) to comply with the thermal requirement for building control but that's also good for the sound proofing. Thanks for any help, I'll post some photos of the new ceiling structure later.

rickybobby wrote:

Hi Stuart, After some hold ups on the rest of the house rennovation we're back on to the studio. We've managed to redesign the roof structure and so we've moved the collars/joists up 400mm so that the underside can be be covered in T&G 22mm moisture resistant chipboard. These will be glued together and joins covered in acoustic sealant. I then propose to paint them with PVA to seal the surfaces. We will make a continuous middle layer(as recommended) which will cover the underside of the joists and on the edges the bottom of the rafters to the wall plate. This then allows us to easily make the internal studwork with the the joists for the inner leaf ceiling supported on the wall plate of the studwalls. My only concern still is sealing the masonry walls in the way you suggested. I understand about what you're saying about concrete blocks being porous but I'm just nervous of creating a potential mould breeding ground by sealing the walls. The cavity will then have no air flow at all as there will be a vapour barrier on the studwall between the rockwool (backside) and the first layer of OSB/STerling board, which is covered with 15mm plastboard (roomside). The top of the cavity is filed with Rockwool slab. This is fire retardant so should also act as a fire stop at the top of the cavity. HAve you ever seen any mould or damp issues when sealing the back of cavity so completely? I do appreciate it's key to good soundproofing in principle, it just seems to go against good building practice? My other question is do you feel 22mm T&G chipboard is enough for the middle layer. The out layer is concrete, slate effect tile so doesn't really do a lot when it comes to soundproofing. I have to fit 300mm RW45 Rockwool slab between my inner leaf and middle leaf (chipboard T&G) to comply with the thermal requirement for building control but that's also good for the sound proofing. Thanks for any help, I'll post some photos of the new ceiling structure later.

Hello Ricky, When specifying your middle ceiling leaf you really need to think of it as your outer leaf. You only have a third leaf to provide ventilation to your roof correct? So your middle leaf needs mass that is quite high to be anywhere near your wall outer mass. You don't need it to be the same. Just massive enough so when it's combined with the large, insulation filled cavity and inner leaf, it will reduce the resonant frequency as low as you need it. Have you worked this out yet, or do you need some help? By the way the requirement for 300mm loft insulation isn't fixed. That is standard low density loft fibreglass. You could probably meet the thermal requirements with less RW45. But besides, you can also fill the cavity between the middle and outer leaf (tiles) with insulation. Just leave 50mm free space between the breather membrane below the tiles and your insulation for airflow. That alone gets you probably 150mm or more of loft insulation, then add the other 150mm (or however much you need to fill your cavity) in the between the middle and inner leaf. Regarding sealing the blocks behind the timber, it's unlikely to have any problems. Consider a timber frame wall, in the UK from inside to out: plasterboard, vapour control layer (impermeable), cavity insulation, sheathing (OSB3), breather membrane, facing. So condensation from inside a room cannot enter the wall. Any (small amount) condensation inside the wall has to work it's way through the OSB sheathing and through the breather membrane to escape. Now your wall: plasterboard/OSB3, Vapour control layer, cavity insulation, block wall sealed. You may notice no permeable surface, which is true, but your inner wall is detached from your outer blocks. This means at the top of your wall cavity it joins the ceiling cavity (between inner and middle leaf) and what is your middle leaf made of? Some kind of wood sheathing (similar to the timber frame wall example sheathing) which the condensation can work it's way through, into your outer cavity which is vented. Now this is probably unnecessary as condensation travels from high humidity to low humidity. If your room has ventilation and aircon then it will have low humidity. If outside is humid your sealed blocks wont let it in the cavity anyway. So the tiny condensation inside the wall is going to just absorb into the insulation and sit harmlessly. If you are worried though, for peace of mind: Use treated C16 timber and galvanised nails to fix them. Thanks, Dan

Soundman2020 wrote:

do I need to add a layer of structural plywood ...

I pretty much always do the walls and ceiling as one layer of thick OSB direct on the studs, then a layer of thick drywall on top of that, possibly with Green Glue damping compound in between if that is needed. That provides excellent sheer strength and rigidity to the wall, and also provides a 100% nailing surface across the entire wall.

I might add some noggins

You HAVE to have noggins! You do need them at least every 48" and preferably every 24".

Just to clarify, at standard height rooms the OSB3 of at least 9mm thickness can provide enough sheer and racking strength to not require noggins at all. (Ref. Structural engineer's calculations for a two story timber frame extension 2014) ... at least in the UK. Noggins provide these protections in place of a structural sheathing material. Thanks, Dan

Noggins provide these protections in place of a structural sheathing material.

Actually, that's not really correct. Noggins do provide nailing surfaces for the horizontal edges of the sheathing, but it's the sheathing itself that provides the actual structural shear strength. Noggins by themselves are not approved in most building codes for providing sheer strength without sheathing. It normally has to be either a sheet of structural sheathing as you mentioned, or some places still allow a diagonal framing member inset across several studs, or other places want steel straps/tension bars on the diagonal, or a couple of others in some places. - Stuart -

Soundman2020 wrote:

Noggins provide these protections in place of a structural sheathing material.

Actually, that's not really correct. Noggins do provide nailing surfaces for the horizontal edges of the sheathing, but it's the sheathing itself that provides the actual structural shear strength. Noggins by themselves are not approved in most building codes for providing sheer strength without sheathing. It normally has to be either a sheet of structural sheathing as you mentioned, or some places still allow a diagonal framing member inset across several studs, or other places want steel straps/tension bars on the diagonal, or a couple of others in some places. - Stuart -

This may be true in the UK too. I'm not sure, as my engineer's calcs were for an open-panel wall frame with sheathing and didn't mention alternatives. Dan

I thought I'd write an update on how my studio build is going. Thanks for all the help so far. After looking at ways to improve the outer lead (middle leaf because of the slate roof tiles) we decided it would be easier to move the ceiling joists up the rafters a bit so we could board out the underside of the joists and bottom section of the rafters. The carpenter lined the underside with 22mm T&G chipboard + 18mm OSB/Sterling board all acoustically sealed on the joins. He also got 100mm of RW45 Rockwool in between the rafters which left a 100mm ventilation gap on the tile side so the soffit vents would still vent the roof space above. We put this insulation in because the gap between the top of the studwork wall plate for the inner leaf and the underside of the middle leaf would be a bit tight on the edges and we needed more insulation for thermal as well as acoustic reasons. The masonry walls were coated with a mixture of PVA and sand to make them less porous. The studwalls are now being constructed and both building control and the structural engineer have agreed that we can cut the ceiling joists diagonally on the ends and still be comfortably able to support the ceiling load of 1 layer of 22mm OSB board + 1 layer 15mm soundbloc plasterboard/drywall (this is also the make up for the walls). The ceiling cavity will have 300mm of RW45 Rockwool in it and the studwalls will have 100mm in them. The ceiling has this much because building control want 300mm for thermal purposes but it can't hurt the sound isolation. The AC unit has been connected and commissioned. I include a photo of this. I'm making a plenum cupboard around this unit as I did in my last studio. basically the cupboard will have a removable panel on the front with a inlet grill on the bottom and an outlet grill in the top. This worked well last time and I took the idea from an contact I met who built studios at the time. Last time I had small room and just had a passive air inlet that was feed through a silencer box I made into the inlet of the AC. This worked well for the size of the room and I was opening the doors enough that stale air moved out ok. This time I have a bigger room and want to approach the air flow better. From reading on here it seems that putting a fan on the outlet is my best option. I can still build an inner leaf silencer box for the passive air intake and feed its output directly to the AC inlet. I could then have a silence on the inner leaf for the outlet and then mount and outdoor fan on the outside of the building to draw the air out. I appreciate that I won't get as good isloation as if I had a silencer on both leafs but I don't think this will be an option. I had good enough isolation last time with the one silencer box. What I'd like to know is a) how do I calculate the dimensions of the silencer box for the size of the room (h =2.4m x w= 3.6m l = 6.8m) b) how do I calculate the fan required to pull adequate air through the room? It looks like this varies with amount of people etc in the room? c) It seems that I connect the pipes coming through the outer leaf to the pipe going through the inner leaf with a flexi ducting? This I assume needs wrapping with insulation to prevent condesation as air travels through the void behind the studwork which will be cooler? Thanks for your help Ricky

Hi, I've been having a good read on the forum about baffle boxes and how people are constructing and installing them. I'm still a little confused. This photo from one of the posts on here confuses me (this studio is a much more professional looking one than mine will be), while it would be great to hide the baffle box in the cavity between the 2 leafs of the studio doesn't this box made out of OSB hard bridge the two leafs together? At the moment I plan to mount both my intake and outlet baffle boxes on the inner leaf. I'm hoping to get enough isolation with this but I can always add baffles to the outer leaf if the isolation isn't sufficient. Something I'm unsure of is as the baffle duct penetrates the inner leaf via some 110mm duct or similar it then needs to connect to flexible ducting which I assume needs to be wrapped in insulation to prevent condensation as the warm air from the room starts to cool as it crosses the cavity between the two leafs? The flexi duct then connects to some more plastic 110mm duct as it goes through the outer leaf and connects to the fan on the outside of the building? Another thing I thought might be a problem is the flexi duct has no mass so any sound waves that makes it through the inner baffle will then be in the cavity? Maybe this is no different than the sound waves that make it through the inner leaf? From what I'm reading the cross section of the baffle box should be at least double that of the ducting pipe I use going through the inner and outer leaf? If I used 110mm then 220mm? I assume that means the opening into the room too? Also should the extraction baffle have the same dimensions as the inlet so going from a 220mm vent in the room down to a 110mm duct through the inner leaf? Here I've done some rough sketches on some photos of where I'm at: extraction baffle position: inlet next to AC unit (in cupboard built as plenum): What the plenum 'cupboard' will look like over the inner AC unit and passive air inlet. Grilles top and bottom are for AC intake and outlet. As always thanks for any help. Ricky

doesn't this box made out of OSB hard bridge the two leafs together?

It sure does, if there's a hard mechanical connection on both sides! It would only be OK if there is some type of resilient decoupling on both leaves (oar at least one of them!)

At the moment I plan to mount both my intake and outlet baffle boxes on the inner leaf. I'm hoping to get enough isolation with this but I can always add baffles to the outer leaf if the isolation isn't sufficient.

Smart plan! :thu: As long as you have the ability to decouple the duct that passes through both leaves, that's fine.

it then needs to connect to flexible ducting which I assume needs to be wrapped in insulation to prevent condensation

Use insulated flexduct:

the flexi duct has no mass so any sound waves that makes it through the inner baffle will then be in the cavity?

Right. Which is why you will probably need silencers on both sides, or a massive sleeve that goes through both leaves and is decoupled on both sides.

From what I'm reading the cross section of the baffle box should be at least double that of the ducting pipe I use going through the inner and outer leaf? If I used 110mm then 220mm? I assume that means the opening into the room too?

Yes, but it's more complicated than that! I'm real short on time to explain now, but I have written about that on several other threads. Hopefully you can find it! There's a whole process of calculation that you need to go through here...

Also should the extraction baffle have the same dimensions as the inlet so going from a 220mm vent in the room down to a 110mm duct through the inner leaf?

Yes, at least! Some HVAC people consider it good practice to make the return duct or exhaust duct a bit larger than the supply duct. But at the very least, both supply and return should be the same: return should never be smaller than supply. - Stuart -

Hi Stuart, Thanks for the fast response, especially as you're short on time.

Right. Which is why you will probably need silencers on both sides, or a massive sleeve that goes through both leaves and is decoupled on both sides.

If I was to build a massive sleeve to go through both leaves please can you point me to some other posts about how to decouple this (having trouble finding an example)? I'm guessing it needs decoupling before it goes through either leaf but then I'm thinking I'm back to the issue I'd have with flexi duct where there's a 'thin' point in the cavity for sound waves to penetrate easily? Possibly I'm best to just go with a baffle box on the outside of the building. I've since had a long read around the forum since I first wrote the above paragraph. I'm confused! I see you saying to someone that

I NEVER pass a duct directly through a leaf. That would be rather silly! The hole and the duct would totally trash your isolation. Instead, I design a wood "sleeve" that passes through the leaf. The wood sleeve has the correct internal cross section, and the duct connects to the end of it, on the other side of the leaf.

I'm confused as to why making a sleeve that passes from the back of the silencer to go through the inner leaf is much different than a well sealed plastic pipe if the silencer box is tightly mount to the inner leaf with no gap behind it? This was what I planned to do. I will change it if it's key to isolation to have a sleeve though? The other bit I'm stuck on is the calculation for cross section of the silencer. The easiest thing for me is to use 100mm plastic pipe through my outer leaf connected to insulated flexi ducting which then connects to another bit of plastic 100mm pipe through my inner leaf directly into the back of my inner leaf mounted silencer box, all leaf penetrations will be sealed with acoustic caulk. Is 100mm pipe for inlet and outlet from the outer leaf sufficient for the size of the room? I have a 100mm core drill bit already bit can rent a bigger one if needed. I understand that the silencer or point where the pipe enters the baffle box should at least double in diameter. Is this true of the reduction on the baffle box for the air output? My flow rate is: h=2.380m x w = 3.545 x L = 6.685 volume = 56.4 m3 Flow rate 56.4 x 6 = 338.4 cubic meters per hour I see from other posts that

speed of air should not exceed 300fps

or 91.44 m/s (not sure this conversion to metric is right though as my results seem crazy!

A = q / v where A = duct cross sectional area (m2) q = air flow rate (m3/s) v = air speed (m/s)

which would mean A = q / v where A = duct cross sectional area (m2) q = air flow rate (m3/s) v = air speed (m/s) a = 339/91.44 = 3.7m ??! where did I go wrong? This is something I need to work out urgently so I can give the carpenter the right information. The silencer boxes will be built out of 22mm OSB with a layer of 15mm around the outside to achieve the same thickness as the inner wall. If I do put a baffle box outside the building what's the best thing to clad these in? I've got plenty of OSB to make them out of but we've just a very nice looking extension done and you would see the inlet baffle box from the front of the house, by the front door :( The wall is white rendered behind it so I'd want to make it blend in as much as possible. Update ------- So I'm having a few issues, I found this before - it's tricky getting trades to work at the level of detail required for a studio build. I've found various timbers touching the outer leaf :( I'm getting those taken out and redone, it's frustrating. Is there a minimum gap I must have between any point on the 2 leafs? 'm referring to where the inner leaf rafters have diagonally cut ends in order to avoid contact with the outer leaf (lower section of roof rafters that are covered with 22mm chipboard and 10mm OSB)? This gap is small but it is a clear gap and my understanding that any break should work? Or am I wrong and vibration will travel across a gap if it's too small? I'm not that happy with this design choice but it was the best we could come up with to maintain the height of the room. See the photo for the gap I'm referring to: I've also noticed that, despite me saying it was key to not leave a big gap at the bottom of the layers, on the inner leaf there are points where it's up to 10mm! I have some backer rod and will get this filled with acoustic caulk but isn't better to to have these floor to ceiling? The floor is a screed with insulation and 2 DPMs so there should be no moisture penetration. I've already got the door design sorted with 2 rubber trunking seals (chrylser type recommended in Rod's book), both doors are oak FD30 with 3/4 " plywood on the back. Both doors also to have strong fire door closers. I may add the magnetic strips if the isolation isn't good enough to the adjoining room but budget is tight so I'll try without first. One thing I've notice is where the carpenter has installed the outer leaf door lining there are the usual gaps between it and the masonry wall. This obviously must be filled with some material with mass. What do you recommend? The gap above the head is quite large. I could have this filled with a concrete mix and the caulk any small gaps/cracks? the sides are a little more tricky and are still too big for caulk. Here's a couple of photos: Separate point --------------- An interesting issue came up with the inner leaf ceiling joists today. When I saw how much the ends needed to be cut on a diagonal to avoid touching the outer leaf (technically my middle leaf that I have because of the tiled roof) rafters that are OSB boarded out for my middle leaf I was concerned about strength to take the weight of my inner leaf ceiling. Here's a photo of the cut joists on sitting on the wallplate. If highlighted the diagonally cut ends in red. Before you panic, I had my structural engineer work out if they could take the sheer load of 1 layer 22mm OSB board + 1 layer 15mm soundbloc plasterboard and it's easily ok with this reduction in timber thickness at the wallplate. I was surprised and asked about 4 times, until he was almost annoyed! Here is the sketch we did for him and a photo of a cut 8x2 rafter held over a piece of CLS (same as used for the wallplate). One diagram shows a single wallplate and the other shows a double. He said either worked but the double plate was a better option so we've gone with that, even though it means the joists got cut thinner to get the diagonal. here's the photo: I thought this was interesting as there's a lot of talk about how heavy these ceilings are, and they are! But I found it interesting that 8x2 rafters at 400mm centres can take this load so easily that cutting the bearing ends down like this is still ok. The structural engineer is highly respected in my area of the UK so I'm sure he's correct. The other thing to factor in, that the structural engineer left out of his calculations but said would help some, is the walls are clad in 22mm OSB which butts right up under the joists providing more support for them as it kind of extends the wall plate inwards. Thought I'd share that last bit as a point of interest. This question is a bit late in the day as we've already started build the studwalls with a vapour barrier but I have been reading some conflicting opinions on vapour barriers. They seem like a good idea in the winter when the room is warm and it's cold outside. Check the vapour on the warmside of the insulation to provent interstitial condensation in the insulation or cavity. But when it's hot outside (not that hot in the English summer!) and cold in the room thanks to the AC then surely the reverse is true potentially leading to condesation on the outside of the vapour barrier leading to damp/wet timbers and insulation in the cavity and roof space? Maybe the AC and air inlet/outlet with fan is enough to control the vapour levels in the room but nothing is controlling them behind the studwalls in the Summer. Because I sealed my concrete bricks on the outer leaf they won't allow much if any vapour to evapourate which means it can only evapourate upwards towards the roof space. It would have to go through my middle leaf of 22mm chipboard + 10mm OSB first though. Maybe I'm overthinking this but I've seen how much water can appear from condesation in the roof of my house when we first bought it and it had no insulation, the rafters were literally dripping until we had the issue sorted and put some ventilation up there as well as insulation. Appreciate your thoughts on this, please keep in mind I live in the UK so that's the climate we're dealing with. Thanks Ricky

I'm guessing it needs decoupling before it goes through either leaf but then I'm thinking I'm back to the issue I'd have with flexi duct where there's a 'thin' point in the cavity for sound waves to penetrate easily?

The way I normally do it is to have a short plywood / MDF / OSB sleeve on the end of the silencer, and that penetrates the leaf, a little way into the cavity. Then there's the flex duct that runs across the cavity and joins up with a similar sleeve on the silencer box on the other side. So the flex duct in the cavity does not matter if it is thick or thin: there's no issue at all if sound gets into it, as the silencer boxes on each side stop it the sound from going further.

I'm confused! I see you saying to someone that

I NEVER pass a duct directly through a leaf. That would be rather silly! The hole and the duct would totally trash your isolation. Instead, I design a wood "sleeve" that passes through the leaf. The wood sleeve has the correct internal cross section, and the duct connects to the end of it, on the other side of the leaf.

Right. The duct itself does not go through the leaf! The sleeve does. If you have a piece of duct going through a leaf, then it creates a huge path for sound to travel through. So the duct does not pass through the leaf: the sleeve does.

I'm confused as to why making a sleeve that passes from the back of the silencer to go through the inner leaf is much different than a well sealed plastic pipe

Because the mass of the leaf is way, way higher than the mass of a thin piece of plastic!

if the silencer box is tightly mount to the inner leaf with no gap behind it? This was what I planned to do. I will change it if it's key to isolation to have a sleeve though?

If you can actually do that without having any gap between the silencer and the wall, then that could work. But you'd have to pretty much glue and caulk the box directly onto the wall to do that. I'm not convinced it would work. However, for high isolation, I normally keep the silencer separate from the wall, resiliently mounted, such that any resonances in the silencer cannot be transferred to the wall, and vice versa.

The easiest thing for me is to use 100mm plastic pipe

I would suggest using proper flex duct or rigid duct. I'm not sure that I'd want to breathe air that passed through something not designed for breathable air... Also,a couple of millimeters of plastic has far, far less mass than the large thickness of wood that you use to make the silencer boxes... Just a small fraction. You might as well not bother building a thick wood silencer box if you are then going to trash all of what you gained, by using a thin walled, low mass pipe to connect it through the leaf...

all leaf penetrations will be sealed with acoustic caulk.

:thu:

Is 100mm pipe for inlet and outlet from the outer leaf sufficient for the size of the room?

For the diameter of the duct that conducts the air outside the room, or between the leaves, that's fine. As long as you slow down the air enough inside the silencer and at the register, that's what matters. It needs to come out the register at slower than 300 FPM.

I have a 100mm core drill bit already bit can rent a bigger one if needed.

You have a 100mm drill bit? That's about 4"! Pretty big. But you don't need a bigger bit to drill a bigger hole. There are several techniques for drilling large holes without a large bit. I can drill a 100mm hole with an 8mm bit.... :)

I understand that the silencer or point where the pipe enters the baffle box should at least double in diameter

Not diameter: cross sectional area. If you double the diameter, you do NOT get double the cross sectional area. For example, if you have a 4" (100mm) diameter duct, and you increase that to 8" (200mm) diameter duct, then you have increased the area from 50 in2 to 201 in2. That's about 4 times the area. Increasing from 4" duct to 6" duct would do it. That's going from 100mm to 150mm. Also, if you have a 100mm round duct and you go to a 100mm square duct, you increase from about 7,800 cm2 area to 10,000 cm2, so without even going wider or higher than the round duct, you already get 25% more by going to square section. A square duct of 125 mm per side will get you 15,600 cm2, which is twice the area of your 100mm round duct.

Is this true of the reduction on the baffle box for the air output?

That depends. If the output goes directly to the register, then no. You need to keep the speed at the register below 300 FPM. So you could go to double the area again (in other words, four times the original area of the duct. But if there's another duct that the connects to the register down stream, you could go back to the same original diameter, then widen it out slowly just before the register. The length of the part that widens out should be at least 5 times the diameter of the duct. So if you have a 100mm duct, you need at least 500mm of wider duct just before the register.

speed of air should not exceed 300fps

That's a typo: it should be FPM: Feet per MINUTE, not feet per SECOND.

(not sure this conversion to metric is right though as my results seem crazy!

You did the conversion right, but the number was wrong. 300 FPM is about 1.5 m/s.

If I do put a baffle box outside the building what's the best thing to clad these in?

You could cover it with fiber-cement board. Something like 4mm or 6mm would be plenty. You can then paint that, render it, stucco it, or whatever you want. I'll get back to you on the rest later. - Stuart -

... rest of reply:

it's tricky getting trades to work at the level of detail required for a studio build.

:) yup!

I've found various timbers touching the outer leaf

:shock: :roll:

Is there a minimum gap I must have between any point on the 2 leafs?

I would aim for at least 1/2", and more if possible. I'm assuming we are talking about the gap between a joist or stud on one leaf, and the surface of the other leaf?

I've also noticed that, despite me saying it was key to not leave a big gap at the bottom of the layers, on the inner leaf there are points where it's up to 10mm!

That should be redone. There should be a small gap there, yes, to be caulked, but not more than about 1/4" or so (6mm, give or take). The fact that there's a large gap, which is also at an angle, tells me that the sheathing was not put up properly at all. The correct method is to place thin shims on the floor, about 1/4" thick, then rest the bottom edge of the sheathing in the shims. After the sheathing is nailed in place, pull out the shims and caulk the gap. If you do it like that, then there's a consist, non-varying 1/4" gap under each sheet, all around the room, and a consistent seal. Repeat that for the second (and additional) layer(s), shimming and caulking each one individually.

One thing I've notice is where the carpenter has installed the outer leaf door lining there are the usual gaps between it and the masonry wall. This obviously must be filled with some material with mass. What do you recommend?

Depends on the size of the gap: if it is something that can be filled with caulk, ten backer rod, then caulk, that's fine. But it if is too big for normal backer rod, then it would be better to use mortar, as you suggested, then caulk once the mortar is completely dry (several days).

I had my structural engineer work out if they could take the sheer load of 1 layer 22mm OSB board + 1 layer 15mm soundbloc plasterboard and it's easily ok with this reduction in timber thickness at the wallplate. I was surprised

I'm surprised too, I must admit. What did your building inspector say about that? Did it pass inspection like that? It seems to me there's not much material at the joist ends. I've heard the "rule of thumb" that taper cuts should never reduce the end thickness by more than half of the original joist height at the joist end, 1/4 height over the other edge of the bearing surface, and the taper should never extend back along the joist more than 3x the joist height. To me, it looks like you have a lot less than 1/2 of the joist height... You say you have 2x8 joists, so by that rule it should not taper down to less than about 90mm at the very tip of the joist, and the taper should not extend more than about 550mm back along the joist. It looks like yours do not meet that. I'd get a second opinion on that. I can't say how things are where you live, but that would not pass inspection where I live. - Stuart -

Ok so if I make the corrections you suggest from my previous post:

My flow rate is: h=2.380m x w = 3.545 x L = 6.685 volume = 56.4 m3 Flow rate 56.4 x 6 changes per hour = 338.4 cubic meters per hour speed of air should not exceed 300fps or 91.44 m/s (not sure this conversion to metric is right though as my results seem crazy! A = q / v where A = duct cross sectional area (m2) q = air flow rate (m3/s) v = air speed (m/s) which would mean A = q / v where A = duct cross sectional area (m2) q = air flow rate (m3/s) v = air speed (m/s) a = 339/91.44 = 3.7m ??!

A = q / v where A = duct cross sectional area (m2) q = air flow rate (m3/s) v = air speed (m/s) max air speed = 300 FPM is about 1.5 m/s 339 flow rate in cubic meters per hour so convert to m3/s 3600 seconds in an hour flow rate =339/3600 = 0.0942m m3/s A = 0.0942/1.5 area = 0.0628m2 or 62.8mm2 this stil seems odd, small?

You have a 100mm drill bit? That's about 4"! Pretty big. But you don't need a bigger bit to drill a bigger hole. There are several techniques for drilling large holes without a large bit. I can drill a 100mm hole with an 8mm bit.... :)

Yup I've done this too in the past with lots of small holes that I then join together but I find it way easier to get a neat hole with a core drill the right size.

I've found various timbers touching the outer leaf

This has been remedied and there is now a good gap at all previous problem points.

I'm surprised too, I must admit. What did your building inspector say about that? Did it pass inspection like that? It seems to me there's not much material at the joist ends. I've heard the "rule of thumb" that taper cuts should never reduce the end thickness by more than half of the original joist height at the joist end, 1/4 height over the other edge of the bearing surface, and the taper should never extend back along the joist more than 3x the joist height. To me, it looks like you have a lot less than 1/2 of the joist height... You say you have 2x8 joists, so by that rule it should not taper down to less than about 90mm at the very tip of the joist, and the taper should not extend more than about 550mm back along the joist. It looks like yours do not meet that. I'd get a second opinion on that. I can't say how things are where you live, but that would not pass inspection where I live.

I''ve had these calulations double checked by my structural engineer (I've messaged you privately with these as I didn't think it was fair to him to share them publically). I've also had them checked by a structural engineer I used before when I lived in another town and he says they're fine. I've also sent them to Building Control and they are happy with them. Odd as it seems when you look at the load per joist it's not that much - 84lbs I think. I weigh double that and wouldn't expect the timber to break or even close if I hung off it. I've also since asked the engineer to add the 300m of 45kg/m3 rockwool in just so I have a legal calculation, there's plenty of headroom in the calc for this though. The key is there can never be any imposed load from above, live or otherwise because the structure is sealed. Noone can ever access the joists. All they will ever support is the inner leaf and rockwool and whatever lights I have. No chandeliers are planned! :)

Hi, We’re just getting on to Building the linings for the internal windows. Because I have to have a sliding internal window I’m having this made by a joinery off site. It will have 10-15mm acoustic laminate glass (depending on price), the joiner understands the seals must be excellent and the frame will be thick pine, I don’t have dimensions yet. That leaves the carpenter to make two linings like the photos you sent me. They will have a gap so they don’t connect the two leafs. I see you advise black cloth over this join, what type of cloth do you find lasts a long time? It would be hard to replace this if it would ever perish? I was wondering if a nylon weave type cloth might be best? Still flexible so doesnt bridge but durable? Update: Having looked at this some more the best solution seems to be to dot n dab (but don't just do dots of bonding, cover the whole masonry cheek) and line it with 15mm soundbloc so it's perfectly level with the inner leaf frame. That way we can make up a double lining with fabric joiner the way you showed and just slide it with minimum gap around with can be sealed with acoustic caulk. Also I don’t see any insulation going in around the frame pics you sent, because this is in the cavity behind the studwall it’s A potential cold spot, what are your thoughts? Talking to the carpenter he was talking about where he would need to use some packers to get the linings in, particularly on the outer leaf against the concrete brick work. What do you suggest filling these small gaps with around the lining? If we make both linings up together and put temporary blocks as show it would be impossible to get anything around the outer frame to seal it. The way you’ve shown is the only to install the fabric across the gap though. Keep in mind my outer layer has triple glazed upvc windows, not ideal but that’s what I have to work with, so the lining will fit up tight to them. Thanks as always for any help Ricky

Hi stuart, Hope you’re well? I was wondering if you could help me work out what thickness glass to have in my internal sliding windows? I have a quote now to have these made up out of tulip wood with quality acoustic seals. My inner leaf is 1x 22mm osb + 1 x 15mm soundbloc. I want to get the Best isolation I can without overspending. If you recall I have triple glazed upvc windows in the outer leaf which is not ideal but I have to live with it for now. It’s possible in the future I might be able to replace these with timber framed windows with a single pane of thick acoustic glass. From what I’m reading i should have the inner windows install in a way to make the air gap between the windows as big as possible? Should the glass panes be sealed in the frames with intumescent tape? Thanks for any help, Merry christmas! Ricky

I was wondering if you could help me work out what thickness glass to have in my internal sliding windows? I have a quote now to have these made up out of tulip wood with quality acoustic seals. My inner leaf is 1x 22mm osb + 1 x 15mm soundbloc.

You need to get at least the same surface density in your glass as you have in the leaf, but in your case even more, due to the outer window problem. OSB is around 610 kg/m3, and drywall is around 690, so you have roughly 13 + 10 = 25 kg/m2 on your leaf. To get the same in laminated glass, it would need to be 10mm thick, but I'd go for much more than that: I'd shoot for 16mm at least, and maybe 18mm if you can get it. In other words, you'd need 8mm+PVB+8mm, minimum, or better would be 9mm+PVB+9mm. You could go with different thicknesses if your glazier offers that: eg, you could go with 10mm+PVB+8mm, or some such.

From what I’m reading i should have the inner windows install in a way to make the air gap between the windows as big as possible?

Right. Whatever the air gap is in your cavity right now (surface to surface, inside the wall, between the leaves), you should aim for at least 20% more, and hopefully 40% more if you can. So for example, of your gap at present is 100mm, then go for at least 120mm between the glass panes, and 140mm would be better. - Stuart -

Hi Stuart, Happy New Year! I'm just working on the baffle boxes with my carpenter now. We've made 2 for the inside (inner leaf). We made them with the 30mm thick collar around the pipe that penetrates the wall and the plasterboard was cut as tight as possible to this. When we fitted the baffle boxes we put some acoustic silicone around the collar so it filled and sealed any gaps. We haven't yet built the boxes for outside yet. I have 2 questions about these. Because the front of the inner baffle box isn't on yet I can see into the pipe that penetrates the inner and outer leaf, the pipe is joined with insulated flexi duct across the cavity between the inner and outer leaves. If you look at the photo you can see condensation in the pipe where it goes through the outer leaf. The outer leaf is made of 2 skins of concrete blocks with cellotex in the cavity. The pipe currently has tape over the outer end to prevent things getting in the pipe. This end will be cut off when the outer baffle box is fitted. Is condensation an issue you see or will the outer baffle box help with this as the warm air from the room will gradually cool down as it snakes it's way through the outer baffle box? The picture is actually the air in so the air will be flowing inwards - cold to warm but the same is happening on the outlet baffle box and pipe. The outer baffle box willl also be lined with AC ducting foam and I'm just concerned this is going to get damp in the water with this condensation and be a potential hazard? The second question is relating to the outer baffle boxes. I assume the front panel needs to be removable so these can be cleaned every now and then? If so how do you make them water tight when covering them with cement board and rendering them? I'm contemplating looking for a ready made box in plastic that coud fit over my baffle box. something like a gas meter box cover but bigger. It would probably be cheaper than making something and more weather tight. In addition to those questions I'm working on the inner window design with my carpenter. I'm not sure if you recall but the inner window also had to open as a means of egress. I was looking at a sliding window design because I also use the 'studio' room for writing software in - my day job. In the Summer it would be good to have the windows open when I'm doing this work as I much prefer to work in fresh air than AC and the summers in the UK aren't very hot. A sliding design would've meant I wouldn't have to worry about what's put near the windows in terms of block it swinging inwards. Anyway I've scrapped the sliding design because noone manufacters good acoustic seals for sliding windows. This is mainly because I think it's hard to do as you can't achieve compression on to the joins between the sashes and the dividing beads. I'm now going for a design where the sashes open inward using parliment hinges which means they can open all the way back and out of the way. I'll be using 3 heavy duty hinges because the sash will weight between 25-30kg with 15mm acoustic laminate glass. I plan to have a double seal the same as my doors. Unfortunately I've run out of the rubber seal which is the Chrysler weatherstripping Rod recommends in his book. I had to order this from the USA as no stocks it hear in the UK and it was expensive with customs tax. I've been looking at other acoustic seals for the windows and wondered if a double seal like the photo of the door with one of these would be enough in terms of isolation. One layer of seal provides 48db of reduction, if I know acoustic laws 2 layers of seal won't be double that but it should be a fair bit better right? https://www.norseal.co.uk/browse/acoustic-perimeter-seals/nor710 Lorient also do a similar seal but it doesn't perform as well. If the chrysler rubber trunking is way better I will of course order some more? I plan to have a latch that pushes the window sash hard on to the seals. Simo's post here is very useful in terms of constructing the windows, he obviously doesn't have an opener but the rest will be great for me. http://johnlsayers.com/phpBB2/viewtopic.php?f=2&t=14814&p=133093&hilit=+glazing+seal#p133093 Thanks for your help Ricky

we made them with the 30mm thick collar around the pipe that penetrates the wall and the plasterboard was cut as tight as possible to this.

It's usually better to leave a small gap all around, a few mm, and fill that with backer rod and caulk, to reduce mechanical transmission. Of course, that also assumes that you mounted your silencer boxes resiliently. But this is already done, and you don't seem to need extreme isolation, so it's probably OK.

Is condensation an issue you see or will the outer baffle box help with this as the warm air from the room will gradually cool down as it snakes it's way through the outer baffle box?

It shouldn't be a problem if you line all your ducts and silencer correctly, with proper duct liner. That's both thermal and acoustic insulation. So the air will not be in contact with cold surfaces until it exits the outside register: then it will dump it's humidity as it hits the cold air outside.

Is condensation an issue you see or will the outer baffle box help with this as the warm air from the room will gradually cool down as it snakes it's way through the outer baffle box?

Make sure that you use a waterproof duct liner! If you are concerned about this, then you could install an HRV or ERV to recover the heat from the exhaust air and return it to the fresh air. And of course, once you have your actual air conditioner running, it will be controlling the humidity inside the room.

The second question is relating to the outer baffle boxes. I assume the front panel needs to be removable so these can be cleaned every now and then? If so how do you make them water tight when covering them with cement board and rendering them?

Your intake register must have air filters on it! To keep out the dust, pollen, particulates, as well as bugs and spiders, etc. Clean/replace the filters regularly. You could also put a filter on the return registers inside the room, for the same purpose: to keep the garbage out of the return ducts. That's less necessary, but still an idea. If you have filters installed properly, and cleaned regularly, then there should be no need to clean out the ducts or silencers.

Anyway I've scrapped the sliding design because noone manufacters good acoustic seals for sliding windows.

These guys do: https://www.schlegel.com/media/flipbook ... 1cb035.pdf Or you could just buy a ready-made acoustic sliding window... :) https://www.rylock.com/uploads/pdfs/Pro ... S_V171.pdf https://bimobject.com/en/atrium/product/atrium-001 http://www.awsaustralia.com.au/vantage/noise-reduction

One layer of seal provides 48db of reduction,

I'd take that with a grain of salt! 48 dB TL on a single barrier requires a surface density of nearly 300 kg/m2! Assuming that the rubber is 1cm thick, it would have to weigh 3000 kg/m3 absolute density.... but normal runner is only about a third of that (around 1200 kg/m3). So either that seal is about 3cm thick at the THINNEST point, or the number is pure marketing hype. 48 dB TL is substantial. Even assuming that the seal is made from magical rubber sprinkled with pixie dust and extruded with purest unicorn hair, you would still only get 48 dB if the window itself can give you that much: Which would require glass that is nearly 20mm thick, in a frame of matching density. Anyway, that stuff you link to MIGHT work, but I'd be skeptical of the high isolation claims. I'd expect something rather more modest than that: maybe 30-somethng dB, which is still pretty decent. Have you looked at the Zero International catalogue? They have a rather decent selection of acoustic seals. There's an entire section of the catalogue devoted to purely acoustic applications, for both door and window seals. - Stuart -