Basement home studio - concrete, flanking and door selection

[mc_deli]

Hi, love the forum, bit nervous about posting this but here goes, advice appreciated;)

I've tried to be detailed with the facts.
-> and added some of my opinions.
Questions at the end.

Goals
Task is to sound proof the “family” music room. It’s mine really! The room is for piano and guitar playing, acoustic guitar/piano/vocal recording, and mixing a variety of genres. I want to be able to record loud singing and mix up to 83dBs with the neighbours and family upstairs barely noticing a tickle from the odd sub kick. When finished the room also has to include a large storage area for music and office equipment, a bed and an electronic drum kit, as well as the usual GAS-fueled home DAW-based recording/mixing set up.

Basement of a 2002 built terrace apartment. Currently the neighbours the other side of the “firewall” can hear hits on my electronic drum pads. ☹

Primary goal is STL @55dB. Secondary goal is to treat the room for mixing (but there are severe challenges/compromises here). Because it is residential I will also keep it “close” to original because of future resale.

01 Dimensions.jpg

Climate
Nordic, from -25 to +25.

Status
The room exists. I have time and money now to work on it. I have all the building plans that show e.g. the firewall construction and products used.

I can do basic framing, drywall and caulking, and basic electrical. I’ll get a carpenter to fit the door(s) and electrician to certify/terminate the wiring (and I will get an engineer’s advice on load bearing for the ceiling if necessary).

I’ve been involved in a commercial studio build previously so I’ve been on here since 2009 and had Rod’s book since 2011. I think I understand the basic concepts.
-> Biggest concerns are keeping it simple, accounting for flanking, choosing the door/s and sourcing the right materials


How loud?
I’ve tested at 85dBs slow weighted with “full range” audio (with every engineer’s favourite, Toxic!)
1. interior wall/door 63
2. exterior wall/window 35
3. firewall (my kind neighbour let me measure) 44
4. ceiling (there is no additional door between the basement room, stairs and lounge above so I can’t currently measure the effect of the ceiling)

So, currently reduction is 22 internal and 41 next door (argh! terrible, more below) and my aim is 55dB reduction for both. And 50dB to the exterior, which I already get.

Detail…
The room is 2520mm high.

02 Original construction.jpg

I’ll stick with the same 1,2,3,4 (it’s a dying art!):

1. Interior wall/door
The interior wall is currently 13mm drywall, 70mm wooden stud, 13mm drywall.
The current double “French” doors lead to the family TV room and have no threshold/seal so sound leaks, hence only @22dB STL through the interior wall/door. New interior and exterior French doors I have looked at have really poor sound attenuation (even if they have great thermal properties for our cold climate).

-> Outer leaf beef up and double leaf, or single leaf with clips/channel, or double leaf with clips channel, all candidates.
-> French doors could be changed to higher STL exterior doors, or sliding doors, double sliding doors, or change the doorway size to one superdoor, or to two high STL doors if double leaf. But sliding doors are very hard to source locally.

2. Exterior wall/window
The walls are a 350mm double leaf concrete hollow block (this model) with a foam filling (51dB claimed). 1200mm of height is underground so is backed by soil etc. There is a narrow window that is 1500mm from the floor and 3160x580mm. It’s triple glazed (it’s cold up here!) and high quality. There is a pipe box in the corner with two removable access panels.

-> I don’t want to add beef up or an extra leaf to this wall and I really don’t want to have to add another window. STL is fine already for my purposes to the outside of the building. The pipe box can be concealed by corner trapping and I will need to build in two access hatches,

3. Firewall
The wall between the apartments’ basements is concrete 200mm hollow block (this model) (62 dB claimed for a finished wall). I can’t break the firewall to check the materials/construction e.g. of the joints with the ceiling or exterior wall. Whatever I do here I can use the same on the whole of the east wall, including the part that is exterior.

-> I could beef up my wall and/or add another leaf with stud or resilient channel or clips/channel. I would prefer channel to maximise room size.

4. Ceiling
Ceiling is 1200mm wide 265mm concrete hollow core resting on the firewalls with 65mm cement layer on top containing electric heating and then tiles for the lounge floor on the next floor up. (I guess this should provide >55dB of reduction as the hollow block alone should provide 45-50).

-> I really don’t know what to do here. The most extreme I could imagine is filling the seams and adding a leaf using channel attached to the existing ceiling and two layers of drywall. But I would rather just fill the seams and beef it up with drywall to preserve height. I think an inside out ceiling would be too complicated for me and cost me too much height.

Floor
The floor is: earth/rock/fill then, 200mm concrete hollow core, 200mm of Styrox, then 100mm of concete with embedded underfloor electric heating, On top are 200mm square ceramic tiles that have an uneven profile and 1.5mm deep grouting seams (that I don’t like at all!). I don’t want to take up the tile floor. There is no door threshold now – the floor just runs under the door to the next room.

->I’d like to floor over the tiles with budget wood-effect laminate for aesthetics/comfort, and to make door framing/threshold easier, thus keeping the original floor intact so it is reversible and I don’t destroy the heating elements. So, I am hoping to find an alternative to levelling compound and use e.g. some kind of mat that will level the floor, some kind of OSB-type baseboard and then laminate.

HVAC
I have a remote control system for the underfloor heating. This room is its own zone and can be turned off.
-> I’ll get an electric radiator and it will be fitted with a control box to join the WiFi enabled heating control app I have.

The best part: the apartment has it’s own ventilation unit. It’s a Vallox ventillation unit that cycles air out from wet spaces and into dry spaces, with variable fan speed and a heat exchanger. It’s not remote controllable or programmable though and the fan is noisy enough to be heard in the room. This room was conceived as a multipurpose room so luckily has in and out vents near the ceiling. I also have a small humidifier in the room to keep guitars happy when the dry cold comes.
-> I swear I will make forum-approved MDF baffle boxes for the in/out vents (really, it’s the only reason I am doing this!!!). I will only do baffle boxes on the studio side and a lot of caulk on the outer leaf as I don’t want to break the ceiling in the hall outside the room.

Power
Because it’s a relatively recent residential build there are many electrical outlets and the apartment is CAT5 cabled with a patch panel in a dedicated technical room.
-> I will remove , re-wire, caulk and surface-mount the four sockets and switches on the interior wall. I’ll fit some lights in the cloud.

Room treatment first thoughts
The room is not rectangular as it’s missing a corner. Ceiling height starts at 2520mm but will be lower with whatever new materials. Large storage space and spare bed mandatory. Mixing position down the long end of the room. Non symmetrical reflection points. These are all issues that are unfortunately unavoidable. This part is going to be a massive compromise – it is the secondary goal after sound proofing.

Room Dimensions: Length=4.65 m, Width=3.5 m, Height=2.52 m
Room Ratio: 1 : 1.38 : 1.84
This is close to Louden 1:1.4:1.9 but I am missing a corner and not firing down the length ☹

-> Bass trapping – I have 10 corners. I would like to make bass trapping as part of the pipe box beef up, something for the other front corner, and something as part of the baffle boxes (i.e. rear wall/ceiling).
-> First reflection points – I’ll make a small cloud above the mixing position and I’ll try to create something for the sides (massive compromise)
-> SBIR – I’ll make a 100mm deep insulation panel/s for behind the monitor position (e,g, the length of the North wall)
-> Rear wall – the bed offers something ☹ and I would like to add trapping to the rear ceiling as part of fitting baffle boxes.

03 Rough room treatment.jpg

Budget
5k euros of which I expect the biggest slice to be the door/doors and their fitting.

Conclusion
Something is causing sound to leak through the firewall. My guess is it’s the construction of how the ceiling hollow core rests on the firewall combined with a flanking path from ceiling to wall to neighbour’s ceiling.

I’d really appreciate some help with the big picture and a good approach, then I can do the material sourcing and work on planning the details of the framing and the joints, and the treatment, and embracing SketchUp.

Questions (apologies for the order)

Does the 55dB reduction goal make sense?

Overall, can I attempt 55dB if I only add the second leaf to the internal wall and firewall i.e. without a full double leaf construction?

Generally, with hollow core and hollow block concrete is flanking nose common and is there are an established cost efficient approach to take, and best practice?

Does the hollow block of the firewall only act as a single leaf – and therefore I should make a second leaf for it, and am I OK with channel rather than framing?

Is the hollow core ceiling also single leaf, is a second leaf a must (the more I look at this I think it is), and is hat channel plus two drywall layers the best compromise – or can I do less?

I am presuming the ext wall is not a flanking problem but if I leave the exterior wall as it is with no extra leaf/beef up is my STL going to be destroyed by flanking where the ext wall meets the original ceiling?

If I do a staggered stud on the interior wall, given my “modest 55dB goal and existing 70mm framing, what is the smallest air gap I could plan?

What door solution? I am bewildered, really lost. While tandem 1500mm patio-style sliding doors might be good if I could find some, should I be thinking two tandem single doors or the other extreme: single superdoor and single leaf?

Overall, what should my walls/ceiling construction actually be?
(Here’s what I can imagine doing myself:
interior wall – basic double leaf staggered stud, insulation, beef up the old first leaf so 2x drywall on each leaf;
exterior wall – as is;
firewall – resilient channel, insulation, 2x drywall;
ceiling – fill seams, second leaf of hat channel, insulation and 2x drywall.)

What is a good idea for the floor – could some kind of mat plus board work as a base for laminate – I am struggling to find references for this – and should I build the floor first in this case and build the inner wall stud framing on some pads (?) on the beefed up floor?

04 New construction idea.png

05 New construction detail.jpg

Phew! Thanks if you made it this far!

[Gregwor]

Does the 55dB reduction goal make sense?

Without doing a true room in a room, I'm not sure that it's possible.

Generally, with hollow core and hollow block concrete is flanking nose common and is there are an established cost efficient approach to take, and best practice?

Flanking is flanking, so yes. A completely decoupled inner leaf would fix this.

Does the hollow block of the firewall only act as a single leaf

Great question. I can't confidently answer that with a firm yes or no. However, the surface density of it is great. There is no way to really deal with any cavities in it and therefore, I would personally treat it as a single leaf.

and am I OK with channel rather than framing?

If you're already having low frequency transmission issues, then a simple answer would be no.

Is the hollow core ceiling also single leaf, is a second leaf a must (the more I look at this I think it is), and is hat channel plus two drywall layers the best compromise – or can I do less?

It's the same as your walls.

I am presuming the ext wall is not a flanking problem but if I leave the exterior wall as it is with no extra leaf/beef up is my STL going to be destroyed by flanking where the ext wall meets the original ceiling?

STL shouldn't be your units of measure here since you need to consider the entire audible frequency range. Flanking will happen there, yes. So you can't just leave that wall as is if you deal with the others.

If I do a staggered stud on the interior wall, given my “modest 55dB goal and existing 70mm framing, what is the smallest air gap I could plan?

A staggered stud wall won't get you 55dB of reduction and deal with the low frequencies you are struggling with.

What door solution? I am bewildered, really lost. While tandem 1500mm patio-style sliding doors might be good if I could find some, should I be thinking two tandem single doors or the other extreme: single superdoor and single leaf?

Mass Law and MSM apply to doors just like walls. Calculate your options as such.

Overall, what should my walls/ceiling construction actually be?

This is up to you to decide what you can afford both financially and time/effort wise in conjunction with what your isolation needs are. There is always going to be a compromise. You just need to set reasonable expectations. Ideally if you're shooting for 55dB of isolation, you need to build a true room in a room and aim for that goal we all seem to shoot for of 60dB. Then, when your construction isn't laboratory spec, you will probably end up in that 55dB range.

What is a good idea for the floor – could some kind of mat plus board work as a base for laminate – I am struggling to find references for this

Any hard material will work great acoustically.

and should I build the floor first in this case

If you're doing polished concrete or epoxy, finishing your floor first is a great idea. Also, it's good to level a really bumpy floor out first as well. Otherwise, put laminate or other materials like that in near the end of the build just like a normal house is finished.

build the inner wall stud framing on some pads (?) on the beefed up floor?

A lot of people suggest that you shouldn't float your walls on pads for a few reasons:
1. price
2. harder to build
3. hard to get an exact weight calculation to properly deflect the material

John Sayers suggests doing it though. In theory, it makes sense to do it, but again, there are cons and a huge risk that you won't compress the pads properly at which point to added a lot of expense and build difficulty for nothing.

Greg

[mc_deli]

Greg

Thanks ever so much for the replies, really appreciate it.

My reaction is:
OK, I accept I need to do more with the ceiling, interior wall and firewall to try for 55dB and mitigate flanking.
Hmm, changing the double doorway to two single doors seems my only option if I can't source sliding doors locally but this is still wide open.
Then, argh, the flanking and, in particular the exterior wall. I really want to avoid building a second leaf on the North and North East exterior walls - and I think I might have some rationale for not doing so.

I don't know how to understanding or calculate the flanking, so here goes - questions at the end - again, really appreciate the help.

Ceiling hollow core slabs

Here's one of the original building plans showing the slabs:

Original construction plan.png

And with some notes to explain:

Original construction plan annotated.png

Flanking paths

There are several potential flanking paths (in order of my guess of what is likely the most severe first):
- Ceiling slab #2 - firewall ( - neighbour's ceiling)
- Ceiling slab #3 (and interior wall) - firewall ( - neighbour's ceiling)
- Ceiling slab #3 (and interior wall) - stairwell (resonant chamber) - firewall ( - neighbour's ceiling)
- Ceiling slab #3 (and interior wall) - stairwell (resonant chamber) - firewall - chimney void in neighbour's ceiling
- Ceiling slab #2 - external wall (neighbour's side)
- Ceiling slab #2 - external wall (neighbour's side) - firewall ( - neighbour's ceiling)
- External wall (neighbour's side) - neighbour's exterior wall ( - or firewall)
- Ceiling slab #1 - external wall (neighbour's side) - firewall ( - neighbour's ceiling)

I don't know exactly what hollow core slabs have been used or how they have been joined and sealed together (horizontally). I am presuming that there is some decrease in flanking transmission between slabs. Some slabs are better designed to limit transmission than others.

By adding a second leaf to the firewall, interior wall and ceiling, I will significantly reduce sound transmission direct via the firewall and also via the stairwell.
Anecdotally, the only noise we hear from neighbours is stair noise, which I presume is flanking noise direct from stairs that is exacerbated by the stairwell and cupboard under the stairs acting as resonant chamber/s.

I note that it is possible that the point where ceiling slab #2, the firewall and exterior wall meet could be significant.

And you can probably see where I am going this... I understand that this is a system and everything works together - but I presume that the exterior wall is the least significant flanking path, and I presume that flanking via slab #1 and exterior wall will be something I can live with when I have treated other flanking paths with the second leaves on interior/firewall/ceiling.

Back to my simplified view, flipped back around:

Ceiling slabs.png

So, that was my rationale for not adding the second leaf to the North and North East exterior wall. It is definitely a compromise. But I think that the complications, cost and time factor of a second leaf with a large window/s are beyond me.

The floor

Quick word about the floor, which is textured tile over concrete embedded with underfloor heating. I think there are three routes:
- Destroy - rip up the tiles, which will mean removing the underfloor heating and then unknown amounts of concrete work to remove/replace and level the concrete floor.
- Level - use levelling compound to level the whole floor. This is not reversible and is probably beyond my capabilities so cost is also a factor
- Overlay - this is my preferred, hence I would like to find the right materials (mat, board)

I don't think destroying or levelling the floor are options for me, hence I want to find a solution to overlay.

EDIT: What I have had in mind is something like "Glen's drum riser" but perhaps lighter, so the floor could be OC703, MDF, plywood, laminate.

One reason I asked about whether to build the inner leaf on the new floor: if I build the inner leaf frame on the existing floor then it will be wood resting on textured tile.

New construction

I appreciate the comment that just the previous staggered stud interior wall, and just channel - no frame - on firewall and ceiling, are limiting STL at lower frequencies. I should sacrifice ceiling height to add frame, clips and channels to help decrease flanking level and frequency.

I am confident I can source hat/resilient channel locally but I don't know about clips (like whisper clips or similar). Non-basic imported materials tend to be pricey here - so clips are a maybe and e.g. Green Glue is probably off the menu.

Here's an update on what the new construction could be:

Interior wall – double leaf staggered stud - existing drywall, stud, beef up drywall, insulation, stud, clips, channel, 2x drywall
Doors - 2x sliding double doors if available, or two single doors
Exterior wall – as is (except the North West wall which gets the same second leaf as the firewall)
Firewall – second leaf - stud, clips channel, insulation, 2x drywall
Ceiling – second leaf - fill seams, stud. clips, channel, 2x drywall
Floor - mat, board, laminate

New construction.png

(EDIT: I could also add the 2nd leaf to the NE ext wall as I presume this would prevent some flanking via slab #2 and the ext wall to the other basement room in my apartment)

Questions

How can I understand, and is it possible to measure, the flanking paths with my meagre resources?

Is it realistic to try to measure the resonant frequency of the stairwell and account for it in case it is a problem?

Do you remotely buy my rationale for not adding the second leaf to the North and North East exterior wall, given my modest goals and budget?

Are clips worth it in my situation or should I just be thinking about stud and channel?

Is the interior wall staggered stud with (clips and) channel a good solution or is there an obvious construction I am forgetting?

Same question about the firewall (West wall) and ceiling - are stud with (clips and) channel a good solution?

I haven't found an example of an inner leaf door framed as part of a wall that uses channel (and clips), could you explain how it works where the door frame meets the drywall?

EDIT: The floor - could the drum riser approach be good - would OC703 or similar be a good material to lay on the tiles before MDF, ply, laminate?

If I do framing directly on the original tiled floor (not on the new floor) then how to fix and seal the frame to the floor?


...Again, really appreciate the help. I've got free time now so I am itching to get into material sourcing - but I realise I have created a conundrum here with the compromises I have got into my head.

[Gregwor]

How can I understand, and is it possible to measure, the flanking paths with my meagre resources?

I'm not aware what units you'd even measure it in per say. The principle is pretty simple though. If one thing is vibrating and touching another thing, both objects are going to vibrate. If the material is very dense (such as reinforced concrete), then there will be a lot of transmission between the two. I mean, even if we were able to calculate some value, it's not going to change anything on your end. You either completely decouple or you don't.

Do you remotely buy my rationale for not adding the second leaf to the North and North East exterior wall, given my modest goals and budget?

I understand your logic, but I still stand by my original statements.

Are clips worth it in my situation or should I just be thinking about stud and channel?

100% clips.

Is the interior wall staggered stud with (clips and) channel a good solution or is there an obvious construction I am forgetting?

That's fine.

Same question about the firewall (West wall) and ceiling - are stud with (clips and) channel a good solution?

Yes.

I haven't found an example of an inner leaf door framed as part of a wall that uses channel (and clips), could you explain how it works where the door frame meets the drywall?

The same will go with every drywall junction (at floors and corners), when you use clips and channel, you leave an 1/8" or so and fill it with caulk. Don't use drywall tape or anything like that because then the sheathing won't float as well and do it's job. So, just caulk at the door jamb.

The floor - could the drum riser approach be good - would OC703 or similar be a good material to lay on the tiles before MDF, ply, laminate?

Yes, it works well. OC703 is great for this because it is a good balance between providing isolation and not being too squishy.

If I do framing directly on the original tiled floor (not on the new floor) then how to fix and seal the frame to the floor?

Lots of caulk.

...Again, really appreciate the help. I've got free time now so I am itching to get into material sourcing - but I realise I have created a conundrum here with the compromises I have got into my head.

Welcome to the chaos and feelings of pressure time-wise.

Greg

[mc_deli]

Greg

Thanks again, much appreciated.

I have a major dilemma then. Basically I am concerned that making a second leaf for the North wall that includes a long window is beyond my capabilities and budget - and that it might take the whole project from minor alterations (where I don't need any permissions) to where I will need some kind of certification because I am affecting the window (I don't know this for sure). On the flip side, of course, there is no way I want to do work on the other walls and ceiling if it will not get results because of flanking.

I feel a bit stuck.

I will try and find some expert advice locally, and try to source a clips/channel solution, and I'll report back.

[mc_deli]

OK I've slept on it. And gone back to Rod's book. And read a mountain more threads on here - including the @gregwor amazing build thread.

It's amazing how one's expectations can change!

I'm going to plan and budget a full double leaf build with fully decoupled walls and the ceiling decoupled via clips+channel.
I can't find a clips+channel system in any local outlets so I will probably have to import.
Window construction is perhaps more straightforward than I was thinking as I only have to focus on one interior window (I am waiting on local pricing for laminate PVB).

New questions:

Duct boxes
I've read a lot of threads on MDF duct boxes. 4 is obviously best - one for each leaf for in and out. I don't want to break my interior wall outer leaf. So, outer leaf duct boxes attached to the the outer leaf between the leaves. Inner leaf duct boxes attached inside the room to the inner leaf. Can I compromise here and just have 2 between the leaves and still aim for 55dB reduction?

Securing the inner leaf framing - sole plates
With the fully decoupled inner leaf sole plates and top plates (the top and bottom of the frame that rest against the floor and ceiling) - how can I secure the sole plates if they are resting on ceramic tile-concrete (which may be embedded with old electric underfloor heating elements) (EDIT: more in the next post on this)?

Securing the inner leaf framing - inner leaf ceiling
I am still think the inner ceiling will be stud-clips-channel-drywall attached to the outer leaf concrete hollow block ceiling because I don't have the room height to use bigger joists to build the inner ceiling so that it's resting on the inner walls - good or bad idea?

Securing the inner leaf framing - top plates
Presuming the inner leaf ceiling is attached to the outer leaf ceiling as above, then should the inner leaf top plates be attached to the outer leaf ceiling - or the inner leaf ceiling frame - or neither?

To clip or not to clip the walls
With the walls and using clips and channel, one of Rod's quotes is ringing in my ears: "I would not bother spending money on an iso-clip system for a wall frame where the studs were already decoupled from one another..... what loss you have via the top plate is going to be the only area where you really see any significant improvement on the system". I think my ceiling will be stud+clips+channel but is the cost/benefit worth it to use clips+channel on the walls?

Door jamb flanking between leaves
In Rod's book and in some other posts I see a gap between the door jamb and the wall framing (in Rod's book it's filled with compressed Rockwool). I don't understand this - with single, double or super door - how is the door jamb secured against the frame (EDIT: for clarity, I mean how is the door jamb secured to the wall framing)?


Thanks,
Alex

[mc_deli]

And a bonus question at the end of this - revisiting the floor, potential flanking via the original floor, and if the inner leaf should be built on the new floor...

I took a look the construction diagrams to check for flanking paths via the floor. Here's the firewall:

Firewall floor plan.png

This shows that each apartment has decoupled hollow core that doesn't meet under the firewall. However, the Styrox (zig zag) and the 100mm of concrete do butt up against the hollow block firewall.

I presume this is not a severe flanking path, but it could affect what to build my inner leaf on.

Then the floor under the interior wall:

Interior wall floor plan.png

This shows that the hollow core sub floor, Styrox and 100mm concrete layer all run under the existing interior stud wall. It's not clear if the ceramic tiles run under the interior stud wall. (I must break the wall to check that.)

I presume this is a serious flanking path.

So, to revisit the earlier comment and try to establish what floor and what the inner leaf should be built on...

and should I build the floor first in this case

If you're doing polished concrete or epoxy, finishing your floor first is a great idea. Also, it's good to level a really bumpy floor out first as well. Otherwise, put laminate or other materials like that in near the end of the build just like a normal house is finished.

build the inner wall stud framing on some pads (?) on the beefed up floor?

A lot of people suggest that you shouldn't float your walls on pads for a few reasons:
1. price
2. harder to build
3. hard to get an exact weight calculation to properly deflect the material

John Sayers suggests doing it though. In theory, it makes sense to do it, but again, there are cons and a huge risk that you won't compress the pads properly at which point to added a lot of expense and build difficulty for nothing.

Greg

Thanks to the comments I am now planning the floor on top of the ceramic tile to be OC703 equivalent, MDF, ply, laminate.

Question:
Should the inner leaf be built on the ceramic tile or on the OC703/MDF/ply to mitigate flanking via the floor under the interior wall, A or B below?

(And then, same as already asked above, if on the ceramic tile, how to secure it - is "lots of caulk" enough to secure it in place to the floor (given that I now plan decoupled inner leaf walls), and does the inner leaf need to be secure to the original ceiling or new ceiling, and how to do that while mitigating flanking..?)

Interior wall inner leaf base detail.png

OK totally pointless question I think! B is ridiculous as I could not rest the weight of the complete inner leaf frame, drywall, all four walls, anything on the walls etc etc... all on OC703-MDF-ply.

So, the construction has to be A in my case, with the inner leaf sole plate directly on the ceramic tile. This makes caulking around the edge of the new floor and under the inner leaf drywall incredibly important. Does it also mean I should consider another more expensive high density material for the floor to try to mitigate flanking...

---> So, the question is a bit wider.... if A is OK for the construction, what (high density?) materials/specials could I consider for the floor to mitigate (low frequency) flanking through the original floor, and is basic caulking enough for the seams, bearing in mind this is an area that it seems justified to spend more?

[mc_deli]

OK totally pointless question I think! B is ridiculous as I could not rest the weight of the complete inner leaf frame, drywall, all four walls, anything on the walls etc etc... all on OC703-MDF-ply.

So, the construction has to be A in my case, with the inner leaf sole plate directly on the ceramic tile. This makes caulking around the edge of the new floor and under the inner leaf drywall incredibly important. Does it also mean I should consider another more expensive high density material for the floor to try to mitigate flanking...

---> So, the question is a bit wider.... if A is OK for the construction, what (high density?) materials/specials could I consider for the floor to mitigate (low frequency) flanking through the original floor, and is basic caulking enough for the seams, bearing in mind this is an area that it seems justified to spend more?

I'm going round in circles. I've just spent another 30 hours reading posts here and elsewhere (many of the same ones I've read on and off for ten years).

I think my ridiculous statement above might be wrong - from other posts it's unclear but I think inner leafs can be built on rigid insulation sub floors. I just can't find a reference.
I am questioning the ceiling - I can't rest the ceiling on the walls because the span would require such deep joists I would lose too much height.

My current thoughts are:

Build the walls on the new floor.
Use OC703 or "Rockboard 60" EU equivalent rigid insulation with high psf rating plus MDF and ply for the floor.
Build a complete decoupled stud frame for the walls (as said, resting on the floor of rigid ins-MDF-ply).
Don't use clips/channel for the walls because of price/performance.
Ceiling - preserve room height - so use a slim profile clip/channel system like this directly attached to the concrete hollow core ceiling.
All walls and ceiling get 2x 15mm fire rated drywall
Laminate PVB 8+8 glass for the narrow windows.
Pair of off the shelf fire rated doors like this

I mocked up the framing and a draft ball park budget:

Framing: 210m of 39x92 = 673,75 (Edit: this is street DIY store price of €3,20 per metre for LVL)
Drywall: 135 pcs of 1200x2750 Gyproc 15mm Fireline = 885,60 (Edit: this is again street price €6,46 m2)
Ceiling clips/channel: 426,80
PVB laminate: 3 x 800x450 8+8mm = 530,00 (6+6mm is half the price)
Doors: 890x2088 = 618,00

Sub total 3207,35 plus some shipping, plus all caulk, all fixings, jambs, floor material, insulation, locks, electrical, MDF, duct liner, drywall hoist hire, structural engineer, plus acoustic treatment, interior fittings (sliding door). But before shopping around and discounting.

I am not disheartened at this. "Total" cost of 5-6k Euros plus impulse purchase is OK.
What is disheartening at the moment is that I have time right now but I am wading through forum posts instead of SketchUp designing or cutting timber!

The biggest question I have is still the floor:

Edit: just found this:

The "cheap" way is to build the floor as a drum riser: Lay OC-703 (or equivalent: Volcan, the makers of Volcanita, makes good stuff here in Chile) across the entire floor, then build a deck of plywood, OSB, or MDF on top of that, at least a couple of inches thick (several layers of wood, screwed together, preferably with Green Glue in between), taking care that the edges of the wood do not touch the walls: leave a gap of a few mm. Fill that gap with flexible caulk.

That works, sort of, but mostly for impact noise, not so much for airborne noise, and you can't build walls on top of that: It's just the floor that is floated, with the inner-leaf walls around it.

...which suggests my ridiculous comment might have been right. Head is spinning at this point... still the question...

Should the walls be built on the new floor and what EU-sourced rigid insulation is the right base material?
(If anyone has seen a reference case for this, would be great.)

[mc_deli]

Rejoice...

I've found a lot of threads with people in the EU looking for OC703 equivalents for "drum riser" floors, and a few where, like me, people don't know if their inner leaf should be on the original floor or on the "drum riser".

Paroc SSB2tjk (manufacturer link).
Owens Corning bought Paroc in 2018. Paroc make all kinds of insulation/acoustic/building materials.
This particular "rigid" insulation board is designed for "our" kind of application.
And "bonus" I have a reference in front of me which is the construction design of a pro studio build using it - with inner leaf walls built on it.

I am so happy.

So, here's a local recipe for the floor:

Laminate flooring (TBC)
Koskifloor p6 22mm tongue and groove particle board
Gyproc GL 15mm flooring plasterboard (x2)
Paroc SSB2tj 50mm step board rigid insulation

I'm now b***s deep in SketchUp and I'm going to base my floor construction and detailed budget on this. However, I can't help but think that securing sole plates to ply/MDF is going to be superior than chipboard/drywall... I will do some more comparing, interested in any experience here.

Meanwhile I discovered I will have to present plans for approval from my housing company so I've reached out to some consultants who can hopefully advise me, provide structural engineering services, and draw up plans.

If (big if) the floor is close to "solved" then my next big question is about the top plates...


Presuming I have a completely decoupled stud wall frame 360 degrees, and ceiling drywall on clips/channel directly suspended from the hollow core ceiling, do the top plates of the stud walls need to be secured to the ceiling (e.g. via isolating hangers or similar) to stop any excess movement between the drywall layers where the walls-ceiling meet?

[Gregwor]

Hey Alex,

Sorry about the late reply. I've been working my ass off and really haven't had much time to spend on the forum. I only have a few minutes here so I won't have time to get to all of your questions. Hopefully some other kind souls on here can help. Thanks for your patience!

Duct boxes
I've read a lot of threads on MDF duct boxes. 4 is obviously best - one for each leaf for in and out. I don't want to break my interior wall outer leaf. So, outer leaf duct boxes attached to the the outer leaf between the leaves. Inner leaf duct boxes attached inside the room to the inner leaf. Can I compromise here and just have 2 between the leaves and still aim for 55dB reduction?

I'm not entire sure I understand your design idea but I think you're saying that you want to place your outer leaf silencers in the cavity between the inner and outer leaf and then you will put your inner leaf silencers inside the room? If so, yes, that's totally fine. Just make sure that you build your boxes out of material that has at least the same surface density as your leaf sheathing. 1" MDF is common for many reasons.

Securing the inner leaf framing - sole plates
With the fully decoupled inner leaf sole plates and top plates (the top and bottom of the frame that rest against the floor and ceiling) - how can I secure the sole plates if they are resting on ceramic tile-concrete (which may be embedded with old electric underfloor heating elements) (EDIT: more in the next post on this)?

John could advise here as he is a firm believer in floating walls. For me, I would just glue the hell out of the connection using something like PL premium and then caulk the hell out of the joint.

Securing the inner leaf framing - inner leaf ceiling
I am still think the inner ceiling will be stud-clips-channel-drywall attached to the outer leaf concrete hollow block ceiling because I don't have the room height to use bigger joists to build the inner ceiling so that it's resting on the inner walls - good or bad idea?

Here are my thoughts on that: If you clip, hat and drywall the ceiling, you're going to lose some height (clips and hat alone eat up some space). Then, your ceiling will need a bunch of panels mounted on it for acoustic reasons. So, there goes a bunch more height. IF you build it inside out, your acoustic height (not visual height) will be the same if not taller than the clip+hat option. Also, you won't have to put a bunch of deep panels on the drywall. You can just stuff the inside out modules/joists with insulation and that's it! In the end, you often end up saving height and end up with a great acoustic response in the room.

Securing the inner leaf framing - top plates
Presuming the inner leaf ceiling is attached to the outer leaf ceiling as above, then should the inner leaf top plates be attached to the outer leaf ceiling - or the inner leaf ceiling frame - or neither?

Legally you will probably have to anchor them to the ceiling (flanking) purely for structural integrity.

To clip or not to clip the walls
With the walls and using clips and channel, one of Rod's quotes is ringing in my ears: "I would not bother spending money on an iso-clip system for a wall frame where the studs were already decoupled from one another..... what loss you have via the top plate is going to be the only area where you really see any significant improvement on the system". I think my ceiling will be stud+clips+channel but is the cost/benefit worth it to use clips+channel on the walls?

If you are building a "room in a room" for your walls, then don't waste time/money/effort using clips+hat. It's already decoupled.

Door jamb flanking between leaves
In Rod's book and in some other posts I see a gap between the door jamb and the wall framing (in Rod's book it's filled with compressed Rockwool). I don't understand this - with single, double or super door - how is the door jamb secured against the frame (EDIT: for clarity, I mean how is the door jamb secured to the wall framing)?

For a single door, you just install a door jamb that will span the distance between both leaves. For two doors, use a door jamb in each leaf like a normal construction would have.

That's all I have time for now

Greg

[mc_deli]

That's all I have time for now

Greg

Thanks Greg, appreciated. Yes to all of that. Super clear.
Duct boxes, yes, just like that. Inner leaf on inner floor is my preferred. Not clipping the walls. Two doors, two jambs, yes.

Top plates: I'll look at some options for securing the top plates to the hollow core ceiling via hangers or other decoupling mechanisms because I think that is my biggest problem flanking path.

Today's biggest topic is then:

Inside out ceiling - to do it or not?

I've considered inside out ceiling and inside out walls for this. Inside out wall for the North exterior wall is very appealing as it would take care of SBIR without losing <100mm to treatment. However, with the walls, I think inside out walls will affect resale buyers unfortunately (drywall inner leaf just means smaller room but inside out inner leaf means weird room and alarm bells for future buyers in 2035!).

I've looked at a lot of inside out ceilings on here and I don't quite understand how I could do a decoupled inside out ceiling.
I don't have the height to use inner leaf ceiling joists resting on my walls.
My understanding I would have to use at least 200mm joists, possibly larger.
I don't want to attached framing directly to the outer leaf hollow core ceiling.
That's why I have ruled out an inside out ceiling so far.

With ceiling treatment I am thinking about a slim cloud above the listening position (like this from Dirk in Belgium) and ceiling/wall corner trapping (like Gareth's here).

I realise I am going to have @60%+ of the ceiling as finished drywall but I see this as a compromise - in order to "defeat" the flanking path through the ceiling and preserve room height. I am 6'3" and I base all subjective height judgements on what I have just christened EWH (Effective Windmill Height). A steady upright power chord windmill requires about 2330mm for me. Ceiling reducto clips and 2x 15mm drywall totals about 90mm "lost" and then floor insulation, 2x MDF/floor drywall, 1x ply/particle and laminate is nudging 110mm "lost".

An inner leaf ceiling height of 2520-90-110=2320mm - well that would be fine!

Question then

How can I do an decoupled inside out ceiling and preserve room height (i.e. without resting ceiling joists on the inner leaf), is there a build on here to reference?

(Meanwhile, back to SketchUp and material sourcing)

[mc_deli]

Today will go down as a good day, even though it rained a lot.

I've spoken to quite a few suppliers in the last few days and I've also been to a warehouse (more below). And I've read so much on here! I've been taking notes and I'll try to compile the best stuff at some point. I think I have a plan and I need a plan, so I also drew a plan! With a bit of luck this could move quite quickly now.

I think I can answer some more of my own questions.
- Top plate anchors - the lovely people at Mason pointed me to "sway braces" (using their DNSB-A and right angled brackets). Sway bracing has also been mentioned by Soundman2020 in a few threads so I feel good about this.
- Inside out ceiling - I think I answered my own question already. I don't have the height to use joists resting on the walls. I don't have the height to use joists at all on the ceiling, hence I like the look of 60mm deep Reducto (clips+channel) with 2x drywall - basic - not inside out.

Big ticket stuff
Structural engineer - don't have one yet but I'm hoping it will be straightforward as I have all the material specs and the house plans have the load bearings.
Designs for my housing company - I've made a first draft (attached here).
Approval from my housing company - hopefully straightforward as it's my near neighbours involved and I have a good relationship with them.

Material sourcing - importing and lead time challenges with special materials:
[*] Ceiling clips+channel - I'm looking at either Genie or Reducto, just because they are in the UK and I can't find anything in Finland.
[*] Sway braces - Mason DNSB-A rubber bolt mechanisms attached to right angled brackets to anchor the inner lead wall frames to the hollow core concrete slab ceiling.
[*] Paroc SSBtj - the rigid insulation for the floor with great load bearing so I can stand the walls on the "drum riser" floor - this isn't cheap but I think it's worth it (could be the longest lead time though)
[*] 15mm drywall - very limited locally, in fact it looks like I am stuck with Gyproc GFL Fireline

...and it took me ages but I've worked out what backer rod is in the local language (it's "pohjanauha" with a "ya" sound for the "hja")
...I haven't got to the bottom of when to use LVL vs dimensional lumber, or which local caulk to go for, or which wall insulation, and if backer rod with a hollow core is OK... soon.

That plan then...
I found an old studio plan and benchmarked that. For you lovely people on John's great forum I've translated all the Finnish terms into English (with the exception of the initials for the cross-section labelling, which are still based on the Finnish).

PDF right here...

Family music room plan.pdf

...and if doesn't look like it was made in some fancy CAD that's because I bent PowerPoint to my will!

In acoustic treatment news
We have a brilliant mineral wool company in Finland called Paroc that was bought by Owens Corning a few years ago. Major construction projects, not typically small fry like me. I ended up in their warehouse today thanks to a friend of a friend and got to rummage through their returns and odds and ends. I filled the car with as much as I could and I have got a variety of felt-faced and open mineral wool slabs that might do for 75% of my treatment needs, for SBIR, cloud etc. Score!

Today's question
LVL vs dimensional lumber - when to use LVL in framing - is it essential at all - I'm looking at 39x92mm wood for all framing with the exception of door jambs - what should be LVL - and what to use for door jambs that's bigger and "load bearing"?

...I guess the other question is if anyone sees a flaw in the plan?

[Gregwor]

Great work man! I can tell you're working your butt off and it's paying off!

...I haven't got to the bottom of when to use LVL vs dimensional lumber

As far as I know LVL is just a lot stronger. It costs a ton more though. I've only ever used/spec'd it for joists. For door jambs I've only ever used Douglas Fir wood. Basically use whatever you can afford that is strong as hell.

or which local caulk to go for

I'm not sure what you have there but sadly the only way to really tell is to buy white stuff that indicates that it is non-shrink/crack. Buy a handful of different models and then try them out. Leave them for a few weeks and see if they shrink or crack. The cheapest, easiest to use and as far as I can see, no shrinking or cracking is DAP DYNAFLEX 230. Chances are you don't have that there though. Just do NOT use Green Glue Sealant. That stuff is horrible. I can't believe they haven't re-formulated it because they continue to sell it. I don't think I've seen a single application of it that hasn't cracked.

or which wall insulation

I can't help you with this one because I have no idea what products are available where you live.

and if backer rod with a hollow core is OK

Yes, that's fine. The backer rod itself offers no real benefit acoustically speaking. It just stuffs in big cracks and prevents you from squirting a full tube of caulk into a crack. So, the caulk just hits the backer rod and then nicely fills your crack to the depth you want.

PDF right here...

Beautiful work my dude!

...I guess the other question is if anyone sees a flaw in the plan?

I think it looks good!

Greg

[mc_deli]

I think it looks good!
Greg

Thanks for the enthusiasm.

I've asked around a bit and it seems LVL might be standard here for all studs - but I'll check some more.
My choice of insulation and caulk will depend on which retailer I end up dealing with.

Overall I am still missing a structural engineer and ideally someone local with some experience that can scrutinise the whole thing against local best practice and regs.

I've updated the plan because I mistakenly put the new floor under the existing wall in the first version and got the dimensions of the legacy/beef up wall wrong (it's only 13mm drywall plus 92 stud = 105mm). Here's the updated:

Family music room plan.pdf

Unfortunately I have a new open issue though - whether or not I need a vapour barrier between the inner and outer leaves for the exterior wall.

Framing in SketchUp

Progress-wise I've got a first draft of the framing in SketchUp:

Family music room frame.jpg

This was a really interesting exercise and well worth the time. It's made me think about e.g. the order of building the walls, insulation width and "off centre" (600 OC here means insulations is sold in 565 widths), access to the pipe box (needs more detail still), doorway and "step" in the outer frame, supports for window and door etc.

I still need to look at some details:
- pipe box access
- door threshold and jambs sizes
- window surround
- framing to support electrical/radiator
- framing to support treatment
- duct boxes size, position and support
- oh and my better half would like an inner leaf window to be openable

The latest big question then is about a vapour barrier


Bearing in mind I am in a climate with min/max exterior -25/+25 and interior +22, and I have the legacy underfloor heating (which could still be used ), and will have an electric wall radiator inside the new inner leaf, and I planned inner leaf windows parallel to the outer leaf windows... will I have a problem with temperature difference in the void between the leaves and do I need a vapour barrier?

[mc_deli]

I've carried on in SketchUp and read a lot more threads on here, GearS***** and e.g. Soundman2020's brilliant reference paper list here that includes ducting and vapour barrier info.

However, I've reached a point now where I need to hear back from local professionals before I continue planning because I might be wasting my time and/or barking up the wrong trees - specifically regarding local regulations, vapour barrier, load bearing and my plan overall.

So, I am waiting to hear if one of the local consultants is going to take my money (please)

Here are the latest sketches:

Framing and rough duct boxes.jpg

Framing and rough treatment.jpg

Screenshot 2020-02-06 at 12.56.34.png

EDIT: I updated this as the first version had a physical impossibility. The 1,2,3,4 is the order of build. AFAIK there have been a few diagrams like this with flaws but I haven't found one that was actually corrected. Hopefully this helps others;)

Screenshot 2020-02-06 at 10.11.44.png

EDIT: SNAFU alert. I misunderstood the application of these sway braces and they should be used to e.g. to anchor inner leaf studs to outer leaf studs. So, the pic is wrong. There are other solutions to anchor top plates to ceiling (such as right angled channel with neoprene like Mason's AB-716 or this decoupling pad from Mecanocaucho.

Screenshot 2020-02-06 at 10.11.31.png

To do list:

- pipe box access - In the corner a 45 degree angled inner leaf wall probably makes more sense for access and it would be the same shape as bass trapping
- doors detail - thinking about moving the door to make more space for a radiator, also thinking smaller doors, I'll look at this in more detail later
- window detail - if one window needs to open then hinges, seals etc. will be required, so it might just be easier/cheaper to use "standard" exterior windows. However, just realised that the existing outer leaf window is made of outer single pane and inner double glazing (with a clever hinge mechanism that means both can open). So, if add the same to the inner leaf I would have a quadruple leaf window construction! My guess is in real world this will be OK as they are only 2x 800x450mm and won't be the weakest link in the build. But I'll come back to this.
- framing to support electrical/radiator/treatment - edit/add framing to be ready for all the inner leaf elements. I feel confident about this. SketchUp is awesome for this.
- framing to support the cloud - some way to anchor the cloud to the inner leaf ceiling, which is "only" 2x drywall on clips/channel directly on concrete. I guess it must be OK to put "lightweight" framing inside the inner leaf attached through the drywall to the furring channel.
- duct boxes size, position and support - my first versions are a bit bigger than necessary. When they are a bit smaller I think the outer boxes will just fit between the leaves. I'm not going to redesign the exact positions until I break open the legacy stud wall and check exactly where/how the legacy ducting runs behind the wall.

On duct boxes
I've read Greg's and Rod's posts and downloaded Rod's design docs, stared at the maths etc. I understand the general concept but TBH I'm lost with Greg's diagram compared to Rod's sizing.

Screenshot 2020-02-06 at 11.00.53.jpg

I'm dealing with 160mm circular ducts. My first stab at these (shown above) are based on a 160x160mm path through the box. However, I understand that I should actually have a much smaller volume for the path to create an "impedance" mismatch. There are so many threads on this but my guess is, like me, pretty much all posters settle on a size plucked from the air without actually calculating in detail. I am thinking if I could get through the volume calculations, how do I choose a ratio for the impedance mismatch? That one design Rod posted has ducting of 286mm with a path that is 206x155mm inside the box. I think I will redesign my boxes roughly based on that ratio.

As said there are so many posts on this, and quite a few dead end threads where posters have made weird and wonderful duct boxes - and this isn't in Rod's glorious book - so, I know I am not alone with this.

Screenshot 2020-02-06 at 10.42.39.png

This diagram is a great way to try and get this across but TBH I just don't get it yet! I'll try again

Building the box and getting the MDF/duct liner sizing is easy in SketchUp - it's "just" this duct size vs path size where I am lost;)

Questions
- Vapour barrier - as in the last post, do I need one, and how does it work where I have the transition between inner leaf that is opposite an internal wall, and inner leaf that is opposite an external all - does that actually mitigate the need for a membrane or does it mean the membrane has to stop where the internal outer leaf starts - does it have to seal the air gap where the external wall stops??

- Other open issues and general errata - any thoughts on where I could simplify, SNAFUs, material choices, any pointers appreciated...?

EDIT: I don't know why this last, old, image appears at the foot of this post - it's not in the content)