John Sayers' Recording Studio Design Forum Archive

Hello all.

I’ve been following the forum for a while now, and gradually building up my knowledge so that when I finally ask for help, I’m not asking the most ridiculous questions. I hope I’m now at that point! Please forgive men if this post goes on a bit, but I’m very keen to provide you with as much useful information as I can...

I’m a composer of hybrid scoring music, and use both a lot of electronic and beat-focused sound combined with classical and organic elements. I also produce trip-hop and dance music.
I’ve recently moved into a mid-terrace Victorian house in East London. The only place I can build my writing/producing/mixing workspace is in the loft - not ideal, I know.

It’s a reasonable size space, and I've had plans drawn up for a basic domestic dormer loft conversion (please see attached - scale bar is in metres).

The room i intend to use is the one named “Bed”. It will be a decent enough size: 2.4m height (this for 2/3 of the length of the room, then the roof will slope back on one end following the countour of the roof at the front of the house - i.e. the section to the left of the Roof Beam on the attached Loft Plan drawing), 5 metres long and 3m wide.

Given the fact that I gather it is nigh on impossible to isolate a space like this without paying an absolute fortune, I am just looking to beef up the basic specification of the floors, walls and ceiling such that I can get enough isolation so that I don’t piss off my wife down below, or the neighbours either side. I don’t monitor particularly loudly (I’m sorry, I don’t have a proper sound meter, but I have an app which tells me that in my mixing position the loudest I ever monitor is around 90dB and on average it’s about 65-70dB). However, I am currently only using KRK V4’s and was planning to buy something bigger - either Adam A7X’s or Dynaudio BM15A’s because i need a larger bass response than the tiny KRK’s (love them though I do) can provide. I’m a fairly thoughtful chap, so I would turn it down when working late. I’m also helped by the fact that we live on a main road, so I imagine this might help drown out some of the sound i produce....

It is also worth noting that I am trying to minimise eating up floor space - not only because I want more acoustic space to work with, but also because when I come to sell the house in a few years time, it will become a bedroom, and it would therefore be preferable if I haven’t created a tiny armoured bunker!

Please refer to the image marked “Loft Section”. The basic conversion specifications done by the loft company are as follows:

Floor:

8”(203mm) by 8”(203mm) steels above the level of the ceiling below, so that the whole conversion is independent of everything underneath. On top of this will be mounted 6”(150mm) by 2”(50mm) wooden floor joists, and on top of this 3/4” (22mm) tongue-and-groove chipboard flooring, followed by carpet underlay and then carpet.

I propose the following upgrade:

- Set the steels on top of some kind of absorbing pad, and pack the cavity they sit in with a similar material.
- Bulk up the floor by using a cement particle board backed with a foam underlay that just floats, unfixed, on top of the floor joists e.g.: http://www.acoustic-supplies.com/produc ... ic-deck-37.
- Use RW45 or equivalent rigid acoustic slabs, friction fitted halfway up the floor joists to provide more air gaps.
- On top of the cement particle boards fit an acoustic underlay e.g.: http://www.acoustic-supplies.com/produc ... impactalay and then fit carpet or hardwood flooring on top.

Walls:

Dormer (outside-to-in) - Slate tiles on battens, 18mm Plywood, 4" by 2” studs (infilled with Celotex insulation), 12.5mm plasterboard, finishing coat of plaster.
Party Wall - 9” brick wall dry lined with 4"by 2” studs and 12.5mm plasterboard, infilled with celotex.
Internal Wall (between bathroom and studio, and also stairwell) - 4"by 2” studs and 12.5mm plasterboard, infilled with celotex

I propose the following upgrade:

- increase thickness of Plywood used in dormer.
- change stud insulation from celotex to either RW45 or equivalent rigid acoustic slabs, friction fitted halfway between studs to provide more air gaps; or alternatively something like this: http://www.acoustic-supplies.com/produc ... ition-wall
- On all walls and studs, use one layer of foam backed board e.g.: http://www.acoustic-supplies.com/produc ... lent-board plus two layers of acoustic plasterboard to give a more massive three-board system. Green glue between these layers?
- Stud foot and head plates to be set on top of isolation strips.
- Dry lined Party Wall to have isolation strips on back of studs where they contact brick.
- Use acoustic sealant to seal up any gaps between studs and boards, and boards and floor/ceiling/walls etc.

Roof/Ceiling

Rafters/ceiling joists insulated with celotex. 12.5mm plasterboard fixed to rafters/ceiling joists. Finishing top coat of plaster.

I propose the following upgrade:

- change insulation from celotex to either RW45 or equivalent rigid acoustic slabs, friction fitted halfway between rafters/joists to provide more air gaps; or alternatively something like this: http://www.acoustic-supplies.com/produc ... ition-wall
- Instead of just one layer of plasterboard, use one layer of foam backed board e.g.: http://www.acoustic-supplies.com/produc ... lent-board plus one layer of acoustic plasterboard to give a more massive two-board system. Green glue between these layers?

I suppose what I’d love to know is:

1.) Are my proposed upgrades any good?!
2.) Should I worry about any sonic issues - resonance, bass build up etc. in the large cavities behind the stud wall created by the chimney brest. (Please see photo, plus see “Loft Plan” which shows chimney breast at top middle - transected by roof beam). If so, do I need to fill these cavities with something?
3.) Should I worry about any sonic issues - resonance, bass build up etc. in the large eaves storage area at the front of the house (created by the very bottom part of the sloping roof).
4.) How do you fix the studs to the floor and ceiling without mechanical fixings that will transfer sound? I propose to set them on isolation strip, but how are they actually fixed?

I would just greatly appreciate it if you think I’m heading in the right direction, or whether you think I’m going to be spending a load of money on fancy materials that are not going to do much with my design!

As I said, it doesn’t need to be professional grade soundproofing, just enough to have a decent dampening affect. I imagine it’s the bass frequencies that are going to cause a problem. Once the studio is constructed, I will then look at acoustic treatment to get the room sounding right.

Thank you so much, in advance, for any pearls of wisdom you may be able to offer. I’m really very excited about getting this project underway, but I confess to being a little daunted by the intricacies of it all.

All the best,

Matt.

Hi Matt, and Welcome!

Sorry about the lack of response on your thread: I somehow missed it, and only just re-found it...

I am just looking to beef up the basic specification of the floors, walls and ceiling such that I can get enough isolation so that I don’t piss off my wife down below, or the neighbours either side. I don’t monitor particularly loudly (I’m sorry, I don’t have a proper sound meter, but I have an app which tells me that in my mixing position the loudest I ever monitor is around 90dB and on average it’s about 65-70dB).

When you get your better speakers, you'll probably find that you don't use them much louder than you do know... the difference will likely be that more of that "loudness" is in the low end of the spectrum, which is harder to isolate. But your levels are very reasonable, and it should be possible to meet your goals. It would be good if you could set up a speaker up there, play loud stuff at 90 dBC, and measure how loud that is at other places in the house where your wife might be, as well as hopefully in your neighbor's place. That will help you figure out how much isolation you are already getting right now, and thus how much ore you need.

I’m also helped by the fact that we live on a main road, so I imagine this might help drown out some of the sound i produce....

Well, then, your solution is simple! Instead of spending lots of money isolation your room, just hire a big heavy truck to drive up and down the street all the time while you are mixing!

Floor: 8”(203mm) by 8”(203mm) steels above the level of the ceiling below, so that the whole conversion is independent of everything underneath.

Just to clarify: that is what you are planning to do? The proposal by the company that you spoke to? Not currently in place? If so, I'm wondering what those steel beams will be resting on, and what type of dead load they will be able to handle. Will the entire studio be supported on those?

On top of this will be mounted 6”(150mm) by 2”(50mm) wooden floor joists, and on top of this 3/4” (22mm) tongue-and-groove chipboard flooring, followed by carpet underlay and then carpet.

OK, so you were planning to put 2x6s on the steel beams, then one single layer of floorboards? Sorry, but that's not going to be a good solution. Neither is the carpet... Carpet is pretty lousy as flooring in a studio, for many reasons.

I propose the following upgrade: - Set the steels on top of some kind of absorbing pad, and pack the cavity they sit in with a similar material.

Right, but that will all need to be calculated carefully by people who understand heavy duty resilient mounts. I'd suggest you should call Mason Industries, and get them involved in figuring out how to mount those beams.

- Bulk up the floor by using a cement particle board backed with a foam underlay that just floats, unfixed, on top of the floor joists e.g.:

That won't actually float the floor, for the following reasons: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173 and even if it did, you would have a situation similar to a three-leaf wall, because the steel beams would already be floated. If you "float on a float", them you do indeed have a 3-leaf system, and the low frequency isolation will not be as good as if you left out one of the resilient layers, and just had a 2-leaf system.

- Use RW45 or equivalent rigid acoustic slabs, friction fitted halfway up the floor joists to provide more air gaps.

You don't want MORE air gaps! You want FEWER air gaps! Every air gap inside your floor is a resonant cavity. The more you have, and the smaller they are, the higher your overall resonant frequency will be, thus reducing your low-frequency isolation. What you describe is a multi-leaf system, which is not only very complicated to calculate and predict, but also provides less isolation than a very simple system that has only one air cavity, with a leaf of mass on either side.

By all means, add more mass to both leaves, yes! That's a good idea. But do not create additional air spaces inside the floor. One air space, to leaves, is the best isolation, least complexity, and most economical.

Here are the equations for two-leaf and three-leaf resonant systems. Imagine what the equations look like for milti-leaf...

Two-leaf: Three-leaf: Keep it simple, and effective, and cheap.

- On top of the cement particle boards fit an acoustic underlay e.g.: http://www.acoustic-supplies.com/produc ... impactalay and then fit carpet or hardwood flooring on top.

Never carpet. It does the opposite of what you need in terms of acoustic treatment in small rooms, and also messes up the psycho-acoustics, so your brain has a harder time determining directionality, and picking up other clues. You might need a throw rug or two as the final "cherry on top" of the room tuning, but not full wall-to-wall carpet.

Dormer (outside-to-in) - Slate tiles on battens, 18mm Plywood, 4" by 2” studs (infilled with Celotex insulation), 12.5mm plasterboard, finishing coat of plaster.
Party Wall - 9” brick wall dry lined with 4"by 2” studs and 12.5mm plasterboard, infilled with celotex.

Not a good plan. Especially for the party wall. You'd be creating a 3-leaf system there too, and therefore possibly annoying the neighbors even more than you are at present, with more low frequencies getting through. Just render the brick (plaster it), to seal it well, then build your inner-leaf wall in front of it.

I propose the following upgrade: - increase thickness of Plywood used in dormer.

Yup. Use two layers of 18mm, preferably with Green Glue in between. Stagger the joints, and caulk them carefully.

- change stud insulation from celotex to either RW45 or equivalent rigid acoustic slabs, friction fitted halfway between studs to provide more air gaps; or alternatively something like this

If you can get Owens Corning OC-703 where you live, then just do all of your insulation with that. Nothing better. You don't need exotic and expensive materials: even though though probably will do the job, they aren't necessary. Common and less expensive materials can do ti just as well, when used properly.

- On all walls and studs, use one layer of foam backed board e.g.: http://www.acoustic-supplies.com/produc ... lent-board plus two layers of acoustic plasterboard to give a more massive three-board system. Green glue between these layers?

Same applies here: nothing exotic Just put RSIC clips on the studs and joists, put standard hat channel in the clips, and screw standard 16mm fire rated drywall (pasteboard) to the hat channel, using standard drywall screws, but only half the schedule on the first layer. Then put a second layer of 16mm drywall over that, with Green Glue, and do the other half of the schedule with screws that are 16mm longer.

- Stud foot and head plates to be set on top of isolation strips

You can if you want, but not really needed. If you do want to go that way, here's how to do it:

- Dry lined Party Wall to have isolation strips on back of studs where they contact brick.

Nope. Nothing should touch that brick wall at all! Just build a stud frame in front of it (after you render it!), then put drywall on that frame, same as above.

Roof/Ceiling: Rafters/ceiling joists insulated with celotex. 12.5mm plasterboard fixed to rafters/ceiling joists. Finishing top coat of plaster.

Just do it the same as the walls: wood frame, clips, hat channel, drywall, green glue, drywall. Simple, easy, inexpensive, effective. All walls and ceiling done the same will get you good isolation.

2.) Should I worry about any sonic issues - resonance, bass build up etc. in the large cavities behind the stud wall created by the chimney brest.

Yes! That's why I suggested the OC-703, for all those wall cavities. If you can't get 703, then use any good quality fiberglass insulation that has a density of around 30 kg/m3, or any good quality mineral wool insulation that has s density of around 50 kg/m3.

If so, do I need to fill these cavities with something?

Yup!

3.) Should I worry about any sonic issues - resonance, bass build up etc. in the large eaves storage area at the front of the house (created by the very bottom part of the sloping roof).

Yep. Same as above. All cavities between your inner-leaf and outer leaf should be filled with insulation. It acts as an acoustic damper on any resonances going on in there, and also attenuates sound moving through it. I also does other good things, such as swapping the way the air acts from isothermal to adiabatic, and makes the path that sound has to take appear longer than it really is. Oh, and it also helps to keep the cold out!

4.) How do you fix the studs to the floor and ceiling without mechanical fixings that will transfer sound? I propose to set them on isolation strip, but how are they actually fixed?

Isosil is one way of doing it, but as I mentioned, that isn't necessary. Firstly, because your floor will already be floated (steel beams on isolation pads, as specified by Mason), so everything built on top of that floor will also be isolated from the building, and secondly because that's what the RSIC clips do for you: They decouple the drywall from the studs. And it's an awful lot easier to throw up the clips and hat channel, than it is to ensure that your stud frame really is fully decoupled from the floor...

whether you think I’m going to be spending a load of money on fancy materials that are not going to do much with my design!

Yep! Not all of it, by any means, but some of it was along those lines. The expensive exotic materials are not necessary for what you are trying to do. They have their uses, but you don't need them.

The most important single thing you can do is to make sure that your outer-leaf is absolutely sealed air-tight all over, after it is finished and before you start on the inner-leaf. Every single gap, crack, and hole must be found and sealed, airtight. Then do the same to your inner-leaf. Sealing correctly is the best thing you can do. And failing to seal is the biggest loss of isolation you can imagine. Even a tiny crack under one sill plate can totally trash your isolation. It's amazing the effect that a simple crack can have...

As I said, it doesn’t need to be professional grade soundproofing, just enough to have a decent dampening affect.

Done as outlined above, you'd be getting that, and more. If you do it right, you'd be getting well over 40 dB of isolation, and probably over 50. That's pretty darn good. Your 90 dB absolute peak level would be at less than 40 dB on the other side, and your typical 75 dB level would be totally inaudible outside.

I imagine it’s the bass frequencies that are going to cause a problem.

yup! For sure.

Once the studio is constructed, I will then look at acoustic treatment to get the room sounding right.

As soon as it is finished, and before you do any treatment at all, or put anything in it, then do yourself a big favor and run the REW acoustic analysis software on your room. It will give you a very clear picture of where all the acoustics issues lie, and what to do about it. Then measure again after you install each treatment device, to see how it is working, and what still needs doing.

I hope all of this isn't too late, and is helpful for you!

- Stuart -

Hi Stuart.

Thanks so much for your detailed response. Very helpful indeed.

So. Here's where I'm at…

The construction company starts building the loft in October.

The loft floor will, indeed, independent form the rest of the house as it is set on top steel beams set into the party walls. I will be using 8 by 2 floor joists, doubled up underneath the partitions to support the extra mass.

Current plan, taking some of your advice into consideration…

Floor construction:

-100mm 60kg/m3 acoustic mineral wool slab (can't get OC-703 here) between ceiling joists of floor below (resting on top of floor below's plasterboard)
- Steel beams, with floor joists set in between the H-shaped profile of them.
- 22mm tongue and groove chipboard screwed into floor joists.

NB* - at this stage I will build the stud walls for the studio on top of the 22mm flooring, the rest of the floor construction is built INSIDE these stud walls (so just in the interior space of the studio):

- 10kg/m3 acoustic membrane contact adhered to the 22mm tongue and groove -
http://www.customaudiodesigns.co.uk/tec ... mbrane.htm

- layer of Isobase resilient layer sat on top of acoustic membrane - with extra left all around perimeter such that it can be skirted up to help decouple the floor from the walls.
http://www.customaudiodesigns.co.uk/isobase.htm

- another layer of 22mm tongue and groove particle board (e.g.: http://www.customaudiodesigns.co.uk/cement-i ... -board.htm) floated (not fixed) on top of Isobase.

- layer engineered hardwood flooring to finish it off.

WALLS and CEILINGS

I know you stated that I should be using resilient channels to decouple plasterboard from stud work, but I really don't want to lose anymore space internally as the room is only 5m long by 3m wide by 2.4m high. With that in mind, I am thinking of doing the following, see what you think!

- 4 by 2 stud walls ( the one on party wall side set a way from brick party wall) filled with 100mm 60kg/m3 acoustic mineral wool slabs
- one layer of 12.5mm acoustic plasterboard screwed to studs.
- one layer of 5kg/m3 acoustic membrane glued on top - e.g. Tecsound SY50:
http://www.customaudiodesigns.co.uk/tec ... mbrane.htm
- second layer of 12.5mm acoustic plasterboard - glued on top of membrane (not screwed).

- same for ceiling.
- EXCEPT - the one pitched ceiling (which is at the opposite end of the new dormer extension) will require 50mm rather than 100mm, 60kg/m3 mineral slab to allow a 50mm air gap between roof felt and insulation - which our building regulations require to prevent moisture build up - it's cold and damp in London, as I'm sure you're aware!)

- all junctures sealed with acoustic sealant.

What do you think?!

Regarding a few things you kindly pointed out:

Quote:

"3.) Should I worry about any sonic issues - resonance, bass build up etc. in the large eaves storage area at the front of the house (created by the very bottom part of the sloping roof).

Yep. Same as above. All cavities between your inner-leaf and outer leaf should be filled with insulation. It acts as an acoustic damper on any resonances going on in there, and also attenuates sound moving through it. I also does other good things, such as swapping the way the air acts from isothermal to adiabatic, and makes the path that sound has to take appear longer than it really is. Oh, and it also helps to keep the cold out!"
[/i]
- the problem I have here is that I can't really fill this eaves storage void with insulation as that area is indeed… for storage. There's no way I'm going to be able to swing it with my better half that all the junk in the house has nowhere now to go because I'm going to be housing mineral wool there! Any other suggestions?! There will also be a few loft hatch doors here going into the storage area - which I was just going to beef up by gluing on some 10kg/m3 membrane and some HDF.

I'm a bit concerned now…

So the areas I'm clearly going to leak sound or potentially get some odd resonances are:

1.) Eaves storage area.
2.) Velux roof window - but am going to upgrade to a sound insulated velux:
http://www.velux.co.uk/products/roof-wi ... insulation
3.) Main studio door - like eaves storage doors - beefed up using membrane and HDF, with a acoustic seals around the frame:
http://www.customaudiodesigns.co.uk/sound-seals.htm
4.) French doors - upspecc with double/triple glazed acoustic glass.

Question you said:

"The most important single thing you can do is to make sure that your outer-leaf is absolutely sealed air-tight all over, after it is finished and before you start on the inner-leaf. Every single gap, crack, and hole must be found and sealed, airtight. Then do the same to your inner-leaf. Sealing correctly is the best thing you can do. And failing to seal is the biggest loss of isolation you can imagine. Even a tiny crack under one sill plate can totally trash your isolation. It's amazing the effect that a simple crack can have…"


What would my "outer leaf" be in the design I have outlined above? In a loft studio my outer leaf is surely the roof itself - which being made of timber rafters and felt then tiles is not really possible to seal up, surely...

Thanks so much for you time, Stuart. Very much appreciated.

All the best,

Matt.

The loft floor will, indeed, independent form the rest of the house as it is set on top steel beams set into the party walls.

Then you have a GREAT opportunity to float it! If your budget is good, you could put isolation springs and pads under the points where the steel beams rest on the walls, and float the entire i9nner-leaf room...

at this stage I will build the stud walls for the studio on top of the 22mm flooring, the rest of the floor construction is built INSIDE these stud walls (so just in the interior space of the studio):

That sounds to me like you are going to build a three-leaf wall! The outer skin of the house itself (walls and roof), are your outer leaf. You only need one more leaf to complete the structure. So you could build that on top of the new inner-leaf floor, and you'd be done. No additional walls beyond that are needed. Adding a third leaf complicates things greatly, since it introduces a second set of resonances, thus driving up the overall resonant frequency, and reducing your low frequency isolation

layer of Isobase resilient layer sat on top of acoustic membrane - with extra left all around perimeter such that it can be skirted up to help decouple the floor from the walls

Did you read the specs?
"It provides excellent reduction in impact noise and vibration, and also a degree of protection against airborne noise". Emphasis mine. That stuff is meant for impact noise, not overall isolation. Here's why: "IsoBase R50 is a closed cell foam...". Nuff said! It is closed cell! Therefore it is not a porous absorber, and cannot provide any meaningful damping for air-borne noise.

Yes, their spec sheet shows that their floor construction is rated fpr 43 dB of isolation.... but they don't bother to mention that more than 38 dB of that comes from the mass of the flooring alone! (two layers of 18mm MDF, aq layer of 10kg/m2 MLV, and the mass of the closed-cell foam). So the resilient properties of that stuff really only provides about 4 dB of isolation, if that, for airborne. It does, however, work very well for impact noise. So if you plan to do some tap-dancing up there, it would be good for that....

I know you stated that I should be using resilient channels to decouple plasterboard from stud work, but I really don't want to lose anymore space internally

??? Resilient channel is 1/2" deep. 12.5mm. You can't afford to lose 12.5mm of room width?

I am thinking of doing the following, see what you think!

- 4 by 2 stud walls ( the one on party wall side set a way from brick party wall) filled with 100mm 60kg/m3 acoustic mineral wool slabs
- one layer of 12.5mm acoustic plasterboard screwed to studs.
- one layer of 5kg/m3 acoustic membrane glued on top - e.g. Tecsound SY50:
http://www.customaudiodesigns.co.uk/tec ... mbrane.htm
- second layer of 12.5mm acoustic plasterboard - glued on top of membrane (not screwed).

I'm thinking that that's a REALLY expensive way to build a lot of complex wall for not very much acoustic isolation! And illegal too. Not to mention unsafe....

Let's take it piece by piece:
- 12.5 mm drywall is too thin for good studio isolation: the mass is too low, it is too flexible, it is too thin, and it has undesirable resonance characteristics. Use only 16mm drywall (plasterboard).
- "Acoustic plasterboard" is much more expensive than ordinary drywall, for little benefit. Sound waves cannot read price tags, so they won't be impressed by how much yo paid for it. The only thing that stops sound is mass: The more mass you have, the better your isolation is. So get the least expensive mass that will do the job! Ordinary fire-rated drywall fits that bill.
- Gluing anything to drywall (plasterboard) severely alters its acoustic and resonant characteristics in unknown and unpredictable ways. For the past many decades, numerous studies have been done in numerous countries on the isolation and acoustic properties of pain old gypsum board / drywall / plasterboard that is NOT glued to anything. It is well understood, bot theoretically and empirically. If you start gluing stuff to yours, you'll be out there all on your own, pioneering an entirely new area of acoustics! So you will become your very own acoustic test lab. The only problem with that, is that nobody knows what the outcome will be. The few studies that have included things glued to drywall, have shown inconsistent and unpredictable results... So if you want to go that way, please do document it well, and write a paper about it: there's a lot of acousticians who would be very interested to see how it works out in your case!
- That "5kg/m2 acoustic membrane" is basically just plain old MLV under a different name. MLV is well known among studio designers, for the great amount of hype its manufacturers produce! It works, yes, because it is mass, and high density. But it is also VERY high priced! Compare the cost of one kg of that stuff, against the cost of 1kg of drywall, and be prepared for a big shock. You could get twice as much benefit from adding another layer of drywall to your wall, at a much, much lower cost.
- "second layer of 12.5mm acoustic plasterboard - glued on top of membrane (not screwed)" That's the illegal part. And the unsafe part. You CANNOT attach one layer of drywall to another with glue alone. You MUST either screw it or nail it, following the schedule found in your local building code. Even if it was legal to glue two layers of drywall together with no mechanical fasteners, that still isn't what you are proposing: You are proposing to glue MLV to drywall, then glue drywall to that... Serious problem there... That is four points of failure... If you do that, please do not ever invite me into your studio: I don't want to be hit on the head by a 35kg sheet of drywall falling from a meter above...!!!

allow a 50mm air gap between roof felt and insulation - which our building regulations require to prevent moisture build up -

Think this through a bit: Yes, your roof deck does need ventilating to prevent condensation, true. You must do that. That's why you have one set of vents under your eaves, and another along the ridge-line of your roof (or gable ends): So the air can get in through the eaves, move past the roof deck, then out through the ridge vents, taking the moisture with it. Great! Except that you are also wanting to use that self-same roof as your outer-leaf... Ummm... How can it be your outer leaf IF IT ALLOWS AIR IN AND OUT????? Answer: it CAN'T! So you cannot use your roof as your outer leaf. Therefore you need another leaf in there some place to act as your outer leaf. Which means you have no choice but to create a three-leaf system. Which complicates matters, but isn't the end of the world...

However, there might be another solution: There are some modern systems for spraying foam directly on the underside of your roof, to prevent condensation from ever forming, in which case you do NOT need the ventilation. So check your building code and talk to your inspector to see if that is permitted. If so, it greatly simplifies things...

- all junctures sealed with acoustic sealant.

Yep! Including the ones at the eaves and the ridge-line...

- the problem I have here is that I can't really fill this eaves storage void with insulation as that area is indeed… for storage. There's no way I'm going to be able to swing it with my better half that all the junk in the house has nowhere now to go because I'm going to be housing mineral wool there!

Then she's going to have to make the choice: Does she want good acoustic isolation, or does she want storage space? She can't have both.... Also, if you have storage in there, then that implies access doors... Problem! How can you have access doors going THROUGH one of your isolation leaves!? Answer: you can't. Or rather you can, but those doors would have to be very massive, special hinges, dual full-perimeter seals, ... the whole 9 yards. That adds a LOT of cost. Once again, that's her call....

2.) Velux roof window - but am going to upgrade to a sound insulated velux:
http://www.velux.co.uk/products/roof-wi ... insulation

That's a double-glazed unit. Two thins pieces of glass separated by a thin air gap, with a very high resonant frequency. That's fine for stopping typical house noise and street noise, but lousy for stopping low frequency music noise. Still, it's better than nothing... And given all the other weak points that you have mentioned, adding one more isn't likely to make a lot of difference.

3.) Main studio door - like eaves storage doors - beefed up using membrane and HDF, with a acoustic seals around the frame:

Once again, that would be a weak point in the isolation, and the pictures on that web site shows only a single seal around the door perimeter, whereas you need at least two seals al the way around.

What would my "outer leaf" be in the design I have outlined above? In a loft studio my outer leaf is surely the roof itself - which being made of timber rafters and felt then tiles is not really possible to seal up, surely...

Exactly! Which is why it looks like your only choice here is to go to a 3-leaf system, which makes it just a bit more complex than I outlined above. But still possible!


- Stuart -

Wow.

I am clearly being very naive.

It looks to me now that there is little point in spending a load of money trying to get this place soundproofed. It is a sieve...

To be honest, it looks like the only thing that might be worth doing is beefing up the floor mass and building the isolated wall (resilient channel - as you say, double or triple layer of 15mm plasterboard - SCREWED not glued :oops) in front of the party wall. Would you agree?

Otherwise I'll be pouring cash into a half-arsed, leaky system. This is not intended to be "the final studio" - rather something to tie me over for three or four years. I guess I'll just need to monitor delicately.

Thank you for all your excellent advice, Stuart. You've been a real trooper!

Matt.

" So the air can get in through the eaves, move past the roof deck, then out through the ridge vents, taking the moisture with it."

It actually works without a forced propellant. It is convection that makes the process work when the hotter air simple rises and the cooler air fills the void, being the more dense of the two, creating the illusion of force air.

Can I ask what you ended up using for your floors, and if it worked? I have a very similar build to yours to do.