John Sayers' Recording Studio Design Forum

I’d like to say thanks for hosting this forum and for all the time you put in to help people.

I’m midway through building a home studio just outside London, UK. The studio location is the basement of my semi-detached Victorian house. The space is not very big but it’s all I have on offer and I’m just trying to make the most of it.
I propose to use this space for writing and recording my own songs and jingles/commercials. Most of the music is guitar based rock. Normally I program guide drum tracks and get them replaced at a session drummer’s studio. I would like to be able to record some drums in my studio if only for writing. If the sound isn’t good enough I’ll carry on replacing them elsewhere.
The height of the basement is limited (final height will be 2.1m) and I have done everything possible to maximise this during the building process so far. I did looking into underpinning but this was too expensive and so I dug down to the bottom of the footings and then back filled from there. This was all done under the supervision of a structural engineer and building control officer.
I was initially advised by an acquaintance who has built and designed many high end commercial studios and works for a large company supplying acoustic materials. Unfortunately he became too busy to continue helping me. I’ve read a lot of the posts here and have found some answers but I have a few more points I need to clarify before the fitter starts lining my basement.
The basement has now been fully tanked and is watertight. There is a lightwell which is also acting as my “means of escape” from the basement. I have had a double glazed window put on the outside top of this, this window opens up and out. On the room side I have had an “tilt n turn” window with acoustic laminated glass in it the inner pane is 8.4mm the outer is a little less. The external window is a normal double glazed unit with toughened glass for building control. The void between these 2 double glazed windows is 1 meter in height and 580mm x720mm. The whole of this void is underground. I know this is going to be a weak point in my design but I have to comply with building regulations by having a "means of escape".

The floor I have put back in was specified by the guy that was helping me. A floating floor design. It has the following build up:
1) Soil
2) 1200 gauge polythene
3) 100mm concrete
4) 20mm profile rubber mat (CDM-UK 43020/10)
5) 65mm Celotex (to meet building regs U values)
6) Vapour barrier.
7) 70mm reinforced screed.
Perimeters have a 10mm CDM-UK rubber strip. This is tape joined to the rubber mat (4) creating a continuous layer separating the screed and celotex from the external structure.
9) The stairwell screed is laid separately to the main room and there is a 10mm rubber perimeter strip between the above screed edge and this one. This is so that the stairs are connected to a separate surface than the main “studio” room. Also a 2nd partition wall and door can be installed on the other side of this join. Hopefully to limit flanking?

The original design was to then have walls made of 3 sheets thick of 15mm acoustic plasterboard attached to studwork supported in deflection heads/C Channels from the floating floor to the ceiling joists above. These would be set in 200mm from the external walls (see the red lines on the attached diagram). 50mm rockwool behind the plasterboard between the vertical batons for thermal and acoustic reasons. 50mm was specified for U value, is there a better material than normal rock wool to use here?

The ceiling was then designed to be suspended using elastomer isolated joist hangers supporting an MF casoline ceiling. 3 overlapping layers of 15mm acoustic plasterboard would then be fixed to the casoline rails. Above this the joist would be filled with 100mm dense Isowool. The edge of the ceiling plasterboards would be separated from the walls by more of the 10mm rubber perimeter strip. This would be a tight butt join but in no way fixed. (see attached diagram)

For the doors I plan to use 2 solid core firedoors possibly upgraded using some of the ideas on this forum, green glue/plywood. The doors will also have thresholds with rubber seals around all edges on the door jamb.
I plan to have a second stud wall with offset studs dividing the stairwell area from the main room. This would mean the inner room stud wall would be build up from the floating floor and the second stud wall (see the blue line on the diagram, basement_floorplan.jpg) would be the other side of the rubber perimeter strip (orange line) that divides the 2 screeds and therefore not on the floating floor. Is this a good design? How much gap should I leave between these 2 walls?

Please can you tell me how the wall batons are best constructed? I was advised to use deflection heads or C Channels to sit these in. The bottom one attached to the screed (floating floor), the top to the ceiling joists above. It was stressed to me that the batons must be fitting using a sliding joint and not to fix these in anyway so as to limit flanking. Looking at some designs on this forum it occurred to me I could run a piece of timber along the top and bottom of these batons and thus make a box structure. This would negate the need for attaching to the ceiling joists? Would it be sturdy enough to take the weight of the plasterboard like this? Or should I do this and sit the cross timbers in the metal C channels as well?

I’ve had a structural engineer I know work out that the ceiling joists are more than capable of taking the weight of all this plasterboard on my suspending ceiling and the other items in the room above. Also that the 70mm reinforced screed can take the load of all the stud work and the doors etc.

I know this isn’t going to be an ideal studio acoustically. I can’t do anything about the low ceiling final height will be 2.1m and the room isn’t far of a square. I’ve been making music for a long time and have always had bedroom studios, I always find that with enough ABing and time I get to know a room I can produce good mixes. My main goal is to achieve enough sound proofing to be able to write and record electric guitars and vocals until 11pm ish and occasionally record drums and have the odd jam without upsetting my neighbours and family. I was told I should be able to achieve 70dB through this kind of wall construction and at most 60dB through the ceiling design? Having read around your forum this sounds optimistic?

I mentioned the window as an obvious weak point. At present the only solution I have is to build a frame in my studwork where the window is and then box around the window, bridge the 200mm void to the external wall with 3 sheets thick of 15mm acoustic plasterboard with the 10mm rubber perimeter strip between the edges and the external wall. Is that going to cause flanking issues? Am I better to put another pane of glass in the studwork? This extra pane would have to be easily openable to pass building control.

I appreciate there are quite a few questions here, thank you in advance for your time in answering them. I hope my crude sketches are enough to go on? I'm going to try a sketchup drawing of what I'm doing.

thanks

Chris

Hi Chris, and welcome!

It's a nice change to see someone come in for the first time with a well-designed isolation plan! Yours is good, and the guy who did it for you knows what he's doing, so rest assured you are on the right track. And yes, if everything is built to those specs and sealed properly, you can indeed expect isolation on the order to of 60 to 70 dB TL: In other words, belting your drums passionately at 115 db will be reduced down to around 50 dB outside. That's pretty decent for a home studio.

Now, having said that, your weak points are as you say: the "escape" window, and the doors. For the escape window, the good thing is the very large air gap between the inner-leaf and the outer-leaf, so adding that third "inner-inner" leaf should not be a problem, even though it will be a third leaf. I'm assuming that this final window or plug needs to be easily removable in order to qualify as your escape route? If so, then maybe you could treat it like a door, with hinges on one side, lots of mass, and at least two seals around it. Some form of catch can hold it in place. It could indeed have a laminate glass pane in it, so you can get the natural light in. Or it could just be plywood / drywall. That's my suggestion on that one. Maybe someone else can come up with other ideas.

If yoru building code allows it, you could actually improve the isolation by filling that entire cavity with insulation. The improvement could be in the range of 5 to 10 dB, theoretically, perhaps even more. The insulation acts as a damper on the MSM system, adds a little extra mass, and actually extends the air path through the cavity, so sound waves "see" a larger effective distance. But there might be restrictions on filling the entire cavity: check your local code to see how much you can put in, and do that.

You can use either mineral wool or fiberglass: If you use fiberglass, the density should be in the region of 30 kg/m3. If you use mineral wool, it should be around 50 kg/m3.

That actually isn't the best way of doing the drywall joints, between wall and ceiling. Rather, you should "interleave" the layers, like this:


You still need to put something to decouple between the edges, of course, but acoustic sealant or caulk is perfect for that, and much easier to apply than a sheet of rubber.


That "sliding c-channel joint" that you describe is a sure flanking path, and is not necessary. If you build the walls correctly, then they do not need to be, and should not be, attached to the ceiling at all. Even a small amount of contact, such as that "sliding" joint, will cause flanking. To give your walls better structural integrity, you could substitute plywood for the first layer of drywall, so you'd have one layer of plywood on the studs, followed by two layers of drywall, instead of having three layers of drywall. Nearly the same overall mass (roughly), but much better strength in sheer, and it also gives you the advantage of having a nailing surface everywhere around the room, instead of having to search for studs to hang stuff.

Then, since your ceiling is not attached to the walls (so you have no joists to provide integrity), you could stabilize the wall tops of your walls with proper sway braces, which are designed to decouple while also stabilizing. That would replace your "sliding c-channel" thing, and improve your isolation.

One other thing you could do to maximize isolation, is to apply Green Glue between your layers of drywall: it enhances isolation in low frequencies.

The bottom plate of the wall frames must be firmly attached to the floor, with anchor bolts. It does not need to be floated in any manner, since the entire floor is already floated.

For the level of isolation that you are aiming for, one seal per door is not enough. I'd go for three full seals on each door.

Anyway, you certainly seem to be on the right path here, and your isolation should be really good, if you build it all according to plan! The pointed I mentioned here are really nothing ore than "tweaks", to optimize your isolation even more.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Wow thanks for the quick reply. Some great tips in it too! I'll definitely switch the join to the one you recommend from the ceiling to the walls. My fitter said he's used to that join for fire regulations anyway.

If I switch the first layer of 15mm plasterboard to plywood what thickness do you recommend? I was using 15mm acoustic moisture resistant plasterboard for my first layer as the external wall of the basement will be prone to small amounts of condensation even though it's been well tanked. I'll make sure the plywood is treated to prevent any problems in the future with damp/condensation. The void will be vented with some small airbricks through the external wall, I'll look into baffling these a bit.


I did some investigations into the sway braces. I found some in the UK http://www.mason-uk.co.uk/basket.asp?pid=415. Stuart at mason-uk was kind enough to draw a diagram to show me how I would install these in my situation. Normally they recommend these are attached to the external wall but I can't do this because mine is a tanked external wall and shouldn't be punctured.
(Added later)Just noticed that the book by Rod Gervais recommends Mason sway braces so it looks like I have stumbled on the right ones.
They recommended the one above and WIC-2, this looks like it has slightly lower performance but is cheaper and may fit my space requirements better?

My original advisor said I needed about 200mm behind my walls. Your recommending to fill that with mineral wool. Building regs will allow this, I just want to double check that it's the best thing to do for sound isolation. I need to be slightly careful of the load I'm putting on my floor. As mentioned this is celotex and 70mm reinforced screed. It should take a fair bit of weight but the mineral wool looks heavy.

In the following diagram I'm showing that I have a brick outer wall on one edge of the basement which is partially above ground. just after it comes above ground level it stops. There is then a void before the floor joists above start. This void is connected to another section of subfloor beneath the same room as the rest of the basement. This section will have no mineral wall between the joists at present as it's not directly over the basement/studio room. Is there any benefit to me bricking this up to just below the floorboards between the joists? I want to maintain some ventilation in the subfloor void. Should I just fill the ceiling joists with 100 dense ISO wool as shown and not worry about extending this wall up a few more coarses? I will have that section of kitchen floor up after the basement is finished from above to work in the kitchen, I could fill these joists will mineral wool then.



I'm now looking into electrics and lighting in more detail. It's not a big room so doesn't require loads. I've asked the electrician for a double socket on each of the walls with 2 double sockets on one next to my desk. Wall mounted sockets so I don't have to cut out holes for all the sockets. I've read a fair bit about putty pads which was a new thing to me, are these something I should be considering? or would wall mounted socket boxes be better?
How much do I need to seal around the cables that come through the plasterboard and is acoustic sealant the best thing to use here?


Because the ceiling is low I was hoping to have 2 moroccan style fretted wall lights for mood lighting and some ceiling lights for bright lighting ( when I loose something etc ;:)
Can you recommend a good way to put spots in the ceiling without compromising the soundproofing and overheating the lights with all the ISOWOOL that's in the ceiling void? Am I better to just wall mount a track of spots? Ceiling height is the limiting factor here and spots would be the choice in a normal room.

Rod Gervais' book just arrived today so I'll be reading his section on lighting tonight!

Thanks again for your help with the sway braces and plywood ideas, that's helped clarify things loads.

Chris

Wow what a journey it's been since I last posted!!

Unfortunately the builder I Was recommended turned out to be a "cowboy"! So many things done wrong and corners cut. Yes he quoted much cheaper than other builders but it wasn't worth it. I've now spent many man hours, with help from my brother, to put right his mistakes.

I first noticed he'd used the wrong length screws to line out the side of the stairs going down to my basement because the points came through the wood paneling into the hall way on the otherside of this wall!! This raised alarm bells as to what screws he might have used to line the suspended ceiling in the studio. I took a few out at random and my fears where confirmed. He's used screws longer than 100m. I'd made it clear that each layer of drywall needed correct length to fix into the the metal rails of the suspended ceiling so that it was secured but that the screws didn't risk going into the timber joist above and therefore flank the ceiling.
My brother and I took the whole ceiling down. Not easy with all the acoustic sealant to preserve the drywall but we managed it. some of the second layer had no sealant on it and the joins that did just had a thin smear over the joins.
Once the drywall was down we could see that the metal suspended ceiling wasn't held to the acoustic joist hangers with locking nuts. Half had already rattle off completely with vibration caused by the movement in the timber joists. This is highly dangerous when you think of the weight of this kind of ceiling, about 500kg - a death trap!! We got to work fixing this and put all the board back up with plenty of acoustic sealant on the joins.
There were many other problems which I wont bore you with. I went to see the builder and ended up getting a fair amount of money back before taking him off the job.
My advise would be either do this yourself or be around for the crucial bits of the build. Things like applying acoustic sealant to each layer. Fixing suspended ceilings to acoustic joist hangers. Anything that is non-standard, oversee it.

So, I'm now at the stage of getting the doors fix and finished properly. I'm installing a back-to-back door with both doors sealed. I have a highly recommended carpenter and joiner for this thankfully. Because I've maintained to separate leafs and the floor in my studio is a floated screed with a rubber perimeter strip separating it from the screed in the stairwell (the second leaf is on this), I would like to separate the door linings above the rubber strip in the floor so there is minimal flanking here. I've attached a diagram of my plan to put the 10mm rubber perimeter strip between them. This would make the join air tight but would it be the best to reduce flanking? My carpenter is asking if he can use a more compressed rubber like the kind they use on conveyor belts?? I think this is too hard and the 10mm rubber strip I have that is more spongey would be better?

Here's the doors as they were put in by the "cowboy" builder, You can see the 10mm rubber perimeter strip in the screed separating them between the 2 door thresholds:


My idea for how to separate the back-to-back door linings:


I've included some photos of my build progress.

A shot before the drywall, showing MF ceiling rails and studwork. You can just see my covered AC unit to the right with water pump beneath:


Here's the same view once the drywall was up and the MDF AC cupboard had been built around the AC unit. You can see the in/outlet vents in the cupboard:



As you can see I have my AC unit mounted internally with an MDF cupboard built around it. This isn't ideal but was the best I could do with my small space. The inlet and outlet ducts and built into the cupboard and will be fully lined with acoustic foam to reduce the noise from the AC (this is a very quiet unit). What I'm aware of is this big cupboard on the wall will act like a drum. Should I fill all the space that I can with Rockwool? I can't fill the inlet and outlet space because this needs to be clear to work but there are some space that I can. What should I wrap the Rockwool in to stop fibres getting into my air supply? Would using thicker MDF across the front make a difference over the 10mm MDF the builder used? Would it help to put some kind of damper between the front of the cupboard and the fixings?

Area around the window:



This area around the window is going to be a weak point in my sound isolation. I have to maintain this as a "means of escape" for building regs. It has some pretty thick glass in it, both panes are slightly differing thicknesses. The window goes into a light well which has another double glazed window on the top. The light well is fully underground to the sides so shouldn't be too much of an issue.
The problem is the lining around the window. I'm proposing that I have a lining made out of exterior grade plywood then a sheet of 15mm soundbloc drywall and then another sheet of plywood. The leading edge that would be up against my exterior leaf (the basement wall) would have the 10mm rubber strip between it and the wall. Is this enough to reducing flanking, any better way to do it? I would then use acoustic sealant over this edge to get a good seal. I need to keep moisture that may form on this exterior leaf off the plasterboard. The cellar has been tanked but there is still a chance of small amounts of moisture through condensation etc.

On the matter of the cellar wall and moisture/condensation I need to provide some ventilation to the void between my leafs. The cellar walls will always "sweat" to some degree and there is always a chance of some condensation between these walls. Although I know ideal both leafs should be as airtight as possible I need to get this ventilation in to preseve the structure over time.

Here is how I intend to get the subfloor ventilation to flow through into the void between my 2 wall leafs in the cellar:


I propose to put 2 airbricks in the wall shown below and acoustically lined ducting off these to reduce sound transfer while still introducing airflow to the void, what do you think? I thought I could even put a right angle bend on the ducting to help further?


Thanks again for all your help on this forum

Chris

Hi again, Chris.

Wow! Lot's of questions in there, all at once! Not sure if I have time to answer them all, but I'll try to cover the major points.

But first, thanks for sharing your sad experience with that builder. More than sad, it is shocking. I'm not sure if there is some type of professional association of builders, or a government organization that oversees them, in the UK, or even a consumer council, but you might want to file a complaint with somebody. It's one thing to have a guy do poor quality work, but entirely another thing when he does obviously dangerous things, such as not using lock nuts on things hung overhead, or using screws that go right through the wall and poke out the other side! There's no excuse for that kind of work, and there must be some way of reporting that, so he can't endanger anyone else's life. Fortunately, you knew enough to suspect problems, and also knew enough to be able to check, but other customers might not be smart enough, and might end up injured, or worse.

Very good advice!

On the issue of the door frames: You don't really need rubber there at all, if you are going to keep separate frames. There's no need for an airtight seal between two doors (only between the doors themselves and the frames. The air between the doors is part of the air between the leaves, so it doesn't matter if that gap between the frames is sealed or not. One easy (and cheap) way to close it off visually is to wrap a piece of semi-rigid insulation (such as 703) with acoustic cloth, and stuff that into the gap between the frames. This is more of an aesthetic issue than an acoustic issue. And yes, you are right about the hard rubber: don't let your carpenter do that, if you want to keep the two frames de-coupled. At best, just use the type of rubber that you find around car door frames, which is a very soft, flexible rubber, but even better is just insulation wrapped with cloth.

One thing that caught my attention: in the photo of the door, there seems to be an electrical cable poking out of a hole in the drywall, right next to the door frame, with anther hole next to it!! What's with that? If you have a hole in your drywall, then you don't have isolation. Even a tiny hole like that can compromise your isolation. You cannot have holes in your drywall. All of your electrical work and signal cabling should be done surface mounted, on top of the wall, and never done with cables poking through holes. You could also do electrical boxes built into the wall and use conduit in the walls for wiring, but then that also needs to be done properly, using putty pads (a.k.a. "putty packs") fully enclosing the sides and rear of each box, and with isolation breaks and seals in the conduit. That has to be during the framing stage, but you already have your drywall on so it's too late for that. Your best bet is to pull all such cables out, carefully fill and seal all the holes, and do everything surface mounted.

Are you sure that's an approved way of mounting your A/C unit? The unit itself might need ventilation around it, and sooner or later you will need to have access to it, for cleaning and maintenance... So check with the manufacturer to make sure you are OK there.

Use proper duct liner for all places that are actually exposed to air flow, and mineral wool or fiberglass for other areas in there that are not exposed to air flow.

Both would be good! The unit itself should be mounted on suitable vibration mounts, with no hard contact between it and the framing or wall surfaces. And the wall should be much thicker than 10 mm. If you are going to add a second layer over that, use 16mm drywall and use Green Glue in between that and the MDF, for extra low-end isolation.

That's not good at all. You'll never know what that moisture is doing inside your wall, until it is too late. That issue should have been dealt with beforehand, from the outside of the wall, to fully seal it, and the builder should also have installed suitable moisture barriers and vapor barriers in the correct places, to prevent condensation from forming. If your plan of providing ventilation is approved by code, and your building inspector already passed it, then I'd still consider using forced ventilation (fans blowing air in / sucking it out again), to make sure you are getting good air flow through that entire area. That should be designed professionally. You don't want to play around with damp inside your walls. What you can add to the system that the pros come up with, is silencer boxes at the points where their ducts go into and out of your wall cavity. It won't be ideal, but will help a lot.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks for the quick answers. Some useful info there. I'm looking into what I can do about the builder complaint.

Hi All,

I'd really appreciate some help with the following 2 questions in my above post:

1) Is my proposed lining around the "means of egress" window the best I can do?

2) Is a 10mm soft rubber strip enough to separate the 2 door linings in my back-to-back door structure.

I have a carpenter who has offered to come in help rectify the problems but he only has limited time so quick help would be much appreciated.

Thanks

I'm not really sure what you are referring to there: Are you saying that you have two doors, back to back, and there is a 10mm gap between the final, finish door frames that you want to hide? If that's the issue, I would just wrap some 703, mineral wool, or fiberglass insulation with some nice looking cloth, and push that into the gap. You could use rubber if you want, but you run the risk of creating a flanking path. It would have to be very soft rubber, cut to just fit in the gap without being forced into place.

Any type of window plug you use there is going to need good seals around the edges, and rubber should work fine, but I'd try to figure a way to get at least two separate and independent seals all around the edge, in two different places. And yes, you do need the same surface density on the plug as you have on the rest of that leaf. But did you check with your inspector to see if your plan is acceptable?

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks for the reply Stuart,

Looks like that's the second issue clear and sorted. I'll do as you say I wrap the mineral wool and fill the gap between the 2 door linings. Is there a minimum gap you would recommend between these 2 linings to separate the leafs or is any break in the flanking path sufficient?

Quote:
1) Is my proposed lining around the "means of egress" window the best I can do?
Any type of window plug you use there is going to need good seals around the edges, and rubber should work fine, but I'd try to figure a way to get at least two separate and independent seals all around the edge, in two different places. And yes, you do need the same surface density on the plug as you have on the rest of that leaf. But did you check with your inspector to see if your plan is acceptable?

I'm not 100% sure as to how I should do the window lining. I understand that 2 seals would be better than 1. The inspector is happy with my plans and is giving me quite a lot of slack so that's not a problem. What I'm not sure about is how I'm going to achieve the same surface density using rubber as a plug if that's key (makes sense that it would be)?
I was going to use rubber so I can decouple the window lining, attached to the inner leaf, from the outer leaf( the basement wall) while creating a seal.
How do I achieve the same density here?



Thanks again

Chris