Garage Conversion - Rehearsal / Recording Room Canberra

[dallew]

Hi,
I have been reading this forum, John’s manual and trawling through other peoples construction threads for the last few months in preparation for my next project - to build a small home studio/rehearsal room for my family and I. I have picked up a lot of good tips looking through this forum but have a few questions that I haven’t been able to find answers too.

Some background…
My wife and I have 4 boys and everyone plays at least one instrument. I am based in Canberra (cold winters and hot dry summers) and I have a fully detached weatherboard garage (9m x 6m) that I built about 10 years ago. The current garage has a small room with soundcheck plasterboard and rockwool insulation that I built for myself to practice in when I constructed the garage. It works OK but it is not big enough for more than 3 people. The rest of the space is pretty much wasted at the moment and we have been thinking what to do with it. Now that the kids are getting older and starting to play in bands we thought we should open up the garage and convert it all into a rehearsal room/studio – come guest bedroom when needed.
The current structure is a detached dwelling on its own concrete slab, a timber stud frame, weatherboard on the exterior and standard wall/ceiling insulation (yellow batts) with 10mm plasterboard. This was one of my first serious home builder projects and I built it as you would a house. It served as a learning exercise for renovating our real house. The roller doors were removed and replaced with wall frame and small windows a few years ago. The shed already has electricity but no plumbing.


The plan…
To start with I want to rip down the small room and open up the garage. I remove the existing windows too.

I would like the studio to primarily be a rehearsal room that is also set up to record a live band or perform multi track recording, then later mix the recording in the same room. I intend to use some of the space for couches etc. to allow for an audience to hang out and watch whoever is rehearsing or for the muso’s to take a break every now and then between songs. The room will also double as a guest room when we have family groups staying with us, packing up the music equipment to make space for a mattress or two. I would like to take a corner out of the studio for a small bathroom that I will have the only open-able window. The general design I want to go with is the room-in-a-room approach (two leaf?). I have not settled on the window locations yet but these will be long narrow windows (3 or 4 of them I am thinking). The basic plan is illustrated below. The exterior will be lined with blueboard over top of the weatherboard. This is purely cosmetic but I figure it will also add mass to the external layer and assist somewhat in attenuating sound. I will also replace the current ceiling insulation with some acoustic insulation (rockwool). Acoustic treatment will be a mix of homemade baffles, acoustic foam and bass traps where needed.
I am not looking to build commercial quality studio but would like something that prevents the neighbors from complaining and also has reasonable acoustics for recording and mixing.

Floor plan

Studio v0.1 - floor plan.png

Section

Studio v0.1 - section.png

My budget is about $15k, including windows and air conditioning. This does not include fitting out the bathroom – this will be done later. I will be doing all the work myself with some assistance from my brother-in-law who is a qualified electrician.

My questions are more around the finer details and I am hoping to get some pointers in the right direction from this forum.

1) Floor
From what I have seen on the forum it looks like it really isn’t worth installing a false floor on a detached concrete slab. I plan on putting down underlay and then laminate wood flooring on top of the slab. Is this correct?

2) Outer leaf
Should I remove the layer of plasterboard from the inside of the outer leaf? I was thinking best to remove the plasterboard and existing insulation then add a strip of plasterboard between each stud against the external weatherboard cladding then adding acoustic insulation (rockwool) with no layer of plasterboard sealing in the insulation. Will this yield a better result over leaving the wall as is and is it worth the trouble? The picture below shows these two options.

Studio v0.1 - legend.png

Side view (cross section)

Studio v0.1 - external.png

Top View (cross section)

Studio v0.1 - external 2.png

3) Air Gap Between Outer and Inner Leaf
I am planning for a 50mm gap between the outer and inner leaf. Will this be sufficient? Examples I have seen show 100mm or more. Do I need a full 100mm?

4) Ceiling
Is it OK to leave the plasterboard on the ceiling of the outer leaf? Does the roof make a third leaf? New false ceiling will be floating on the internal leaf wall frames with rockwool insulation.

Studio v0.1 - ceiling(e).png

4) Windows
I am planning to have a few windows in to let in some natural light. I am thinking about making my own windows using timber and a couple of panes of glass. Should I build these as two separate windows in each leaf (as below)? Or is it ok for the window frame to span both leaves? Is it better to use a single piece of really thick glass or two thinner pieces. Picture below.

Studio v0.1 - window.png

6) Double Plasterboard
When installing two layers of plasterboard I am assuming that I should joint the first layer as normal but using a flexible sealant and backer rod in the corners. When adding the second layer is it OK to screw the second layer through the first and into the studs or should these be glued?

7) Ventilation
I am a little concerned about ventilation and fresh air into the room. I am considering building an intake (lower in the room) to let fresh air in and an exhaust higher near the ceiling to suck out stale air. The intake/exhaust duct/pipe will be wrapped in insulation and on the exterior will run through a maze box lined with insulation. Will this sort of ventilation provide enough sound isolation while maintaining a path for air to get in and out?

Studio v0.1 - ventalation.png

8) Air Conditioners
I have seen a Daikin split system (US7) that has a fresh air intake that I am considering using to both condition the air and inject fresh air. This would remove the need for the ventilation intake/exhaust mentioned above. From what I can see this seems to be the only unit that supplies fresh air in a small split system. They are expensive though. Has anyone come across other manufacturers that make smaller split systems with fresh air intakes.

Hopefully some readers of the forum have some advice in some of these areas.

Dalle.

[BN1studio]

I think I'd take down the interior partitions but build a little extension on one side for a bathroom, storeroom, entrance lobby, etc, etc. Maybe even a bedroom as well?

That way the two parts could be separate & more useful and the playing room would be bigger

Like this

studio_extension.2.jpg

Nick Froome

[Soundman2020]

Hi there "dallew", and Welcome to the forum!

A very, very belated "welcome"! I'm not sure how I missed your original post, and I wanted to apologize for that... I only just saw it now, due to the rather questionable "advice" offered above. I'm hoping you are still around, and still want answers to your questions that you posed here. If so, please let us know, and I'd be glad to respond in full.

- Stuart -

[dallew]

Hi, Stuart.
I have had to delay construction starting until around May this year.
Still very keen to get some advice on my questions and overall design.

Dalle.

[Soundman2020]

I think I'd take down the interior partitions but build a little ...

"Nick", In what way does that extremely unhelpful reply, answer any of the OP's original questions? In what way would it be even slightly useful?

- Stuart -

[Soundman2020]

Hi Dalle. Cool! Glad to hear you are still around.

Basically, you are on the right track, but let me cover all bases:

The current structure is a detached dwelling on its own concrete slab,

Excellent! No flanking to the main house, or anything else. Great start.

I would like the studio to primarily be a rehearsal room that is also set up to record a live band or perform multi track recording, then later mix the recording in the same room.

That is possible, but it all depends on what you mean by "mix". The acoustics that you need for band rehearsal and the acoustics that you need for a pro-level studio are two very different things. If you wanted to mix for commercial purposes, then that might be an issue, as the acoustics would be too live for that. If you just wanted to mix demos for friends and family, then that would probably work out fine using "live room" acoustics, but understanding the limitations that would impose on the mixing process.

I intend to use some of the space for couches etc. to allow for an audience to hang out and watch whoever is rehearsing or for the muso’s to take a break every now and then between songs. The room will also double as a guest room

Here's a suggestion: make those couches the type that have fold-out beds inside them! They work pretty well.

The general design I want to go with is the room-in-a-room approach (two leaf?).

I have not settled on the window locations yet but these will be long narrow windows (3 or 4 of them I am thinking).

Studio windows are hard to do. Actually, I'd say they are a pain to do! So it would be better to have fewer larger windows, rather than a large number of small windows...

The exterior will be lined with blueboard over top of the weatherboard. This is purely cosmetic but I figure it will also add mass to the external layer and assist somewhat in attenuating sound.

If you wanted it to be as good as possible, seal up that weatherboard first, with abundant caulk between the planks, and a coat of paint afterwards. Not or aesthetics! For acoustics. It doesn't have to look nice, as it will be hidden by the blueboard.

My budget is about $15k, including windows and air conditioning.

Might be tight... HVAC ain't cheap, and neither are windows and doors.

1) Floor
From what I have seen on the forum it looks like it really isn’t worth installing a false floor on a detached concrete slab. I plan on putting down underlay and then laminate wood flooring on top of the slab. Is this correct?

Very correct: Floating a floor properly would blow your entire budget, and then some more... and you do not need it anyway!

2) Outer leaf
Should I remove the layer of plasterboard from the inside of the outer leaf?

Yes!

I was thinking best to remove the plasterboard and existing insulation then add a strip of plasterboard between each stud against the external weatherboard cladding then adding acoustic insulation (rockwool) with no layer of plasterboard sealing in the insulation.

Yes!

Will this yield a better result over leaving the wall as is and is it worth the trouble?

Yes and maybe. Yes it would improve the result, but "maybe" it would be worth the trouble. That's a lot of effort to do that... It works, but it's a LOT of slow, boring, mind-numbing repetitive work, cutting all those pieces of drywall to fit between the studs, sealing, caulking, cleats, rinse, repeat... If you need high levels of isolation, then it is worth it. If not, then you probably don't need to do that... PROVIDED THAT you get a perfect seal on the existing weatherboard and the new blueboard. If you don't or can't seal those perfectly air-tight, then you DO need to do the boring, mind-numbing thing....

3) Air Gap Between Outer and Inner Leaf
I am planning for a 50mm gap between the outer and inner leaf. Will this be sufficient? Examples I have seen show 100mm or more. Do I need a full 100mm?

A lot of people get confused about what the "air gap" actually is: It is the full distance across the cavity between the leaves, from the interior surface of the outer leaf to the interior surface of the inner leaf. If your studs are 90mm deep, and you leave a 20mm gap between the original stud frame of the outer leaf, and the new stud frame for the inner leaf, then your air gap is already 90 + 90 +10 = 190 mm. That's excellent (in your case, subtract the thickness of the "beef-up" drywall between the outer-leaf studs, but that's still a very nice size air gap).

It is still considered to be an "air gap" even if you fill it with insulation (fully or partially). Insulation is mostly air in any case, so filling the cavity does not make it any less of an air gap.

4) Ceiling
Is it OK to leave the plasterboard on the ceiling of the outer leaf? Does the roof make a third leaf? New false ceiling will be floating on the internal leaf wall frames with rockwool insulation.

Yes, that's fine. technically, the roof is a third leaf, but in reality it is so far away from the other two leaves that it does not have much of a "third leaf" effect. Don't sweat it.

However, I would suggest that you add another layer of drywall to the ceiling, below the existing layer, to get some more mass up there. A single layer by itself is not going to be enough.

4) Windows
I am planning to have a few windows in to let in some natural light. I am thinking about making my own windows using timber and a couple of panes of glass.

Should I build these as two separate windows in each leaf (as below)?

Yes! Absolutely! that is indeed, the correct way to do it. For maximum isolation, use laminated glass that is the same surface density as the leaf that it sits in, or a bit more.

Is it better to use a single piece of really thick glass or two thinner pieces. Picture below.

It's better to use two THICK pieces! the concept here is that the glass should have the same surface density (kg/m2) as the rest of the wall that it is in, such that the isolation is constant across the entire surface of the wall, with no variations. Since glass is about three times the density of drywall, it only needs to be about one third the thickness. So if you end up with two layers of 16mm drywall on your inner leaf, then the glass you need for the inner leaf should be (16+16)/3 = 11mm thick. To be safe, get 12mm laminated glass, made up from 2 pieces of 6mm glass bonded together with an acoustic PVB membrane in between. The glass for your outer leaf would be figured out n the same manner.

6) Double Plasterboard
When installing two layers of plasterboard I am assuming that I should joint the first layer as normal but using a flexible sealant and backer rod in the corners. When adding the second layer is it OK to screw the second layer through the first and into the studs or should these be glued?

It MUST be screwed (or nailed) all the way through. Gluing a second layer of drywall on top of the first layer is probably illegal, and is definitely unsafe, especially for the ceiling. It would eventually delaminate and fall... on your head!

Screws are needed. Check what your building code says about this, but normally you can use one third the screwing schedule on the first layer, and two thirds on the second layer. In other words, if the schedule says that you need a screw every 20cm, then put one screw every 60 cm on the first layer, and one every 15cm on the second layer, lined up so you get them evenly distributed. But check to see what code allows. You might need a full schedule on each layer.

7) Ventilation
I am a little concerned about ventilation and fresh air into the room. I am considering building an intake (lower in the room) to let fresh air in and an exhaust higher near the ceiling to suck out stale air. The intake/exhaust duct/pipe will be wrapped in insulation and on the exterior will run through a maze box lined with insulation. Will this sort of ventilation provide enough sound isolation while maintaining a path for air to get in and out?

Yes... IF you do it right! You need to do some math here: you need to calculate how much air you LEGALLY need to move through the room, as specified by code, or if code doesn't say, then how much you should REASONABLY move through there, based on commonly accepted parameters. With that number in hand, you need to settle on the maximum air speed that you will allow at the supply and exhaust registers, since fast moving air is noisy, and slow moving air is not. With those two numbers in hand, you can figure the sizes of your ducts. And with all of that in hand, you can figure our the dimensions of your silencer boxes. And with all of that in hand, you can estimate the static pressure drop that all of this will create, based on which you can finally select the fan that will provide the correct flow rate at the correct air speed when faced with that specific static pressure..... There re no shortcuts here, I'm afraid: Better get our your pencil, paper and calculator!

Air Conditioners
I have seen a Daikin split system (US7) that has a fresh air intake that I am considering using to both condition the air and inject fresh air. This would remove the need for the ventilation intake/exhaust mentioned above

Not really... those units do bring in a bit of fresh air, but they don't take any stale air out: you'd still need to have exhaust ducts, and you'd still need to do the math.

They are expensive though. Has anyone come across other manufacturers that make smaller split systems with fresh air intakes.

I would suggest saving your money and going with a simpler, less expensive unit that does not supply fresh air: do that yourself with your own duct system. It isn't that hard to figure out.

- Stuart -

[dallew]

Thanks for the taking the time to offer some tips. Looks like I am mostly on the right track which is reassuring.

The room will mostly be for live rehearsal. Certainly not looking to get commercial grade mixing from the same room but I am looking to do some basic mixing. If any of the kids ever do get this serious then I can construct and fit out a dedicated mixing room where the couches are going to be initially.

We have decided not to cover the outside with blue-board so I will definitely line the inside of the weatherboard to get a good seal. I am thinking of using MDF rather than plasterboard because of the increased in density.

I will add an extra layer of plasterboard to the existing roof. – Great suggestion, thanks.

Thanks for the additional information on the windows – very helpful. I didn’t know about the need to maintain the density.

Ventilation – thanks for the info. Any tips on where to where to find the calculations for the dimensions and air flows (I am sure they will be somewhere in the forums?).

Based on what you have said I will just go with a standard air conditioner with the ventilation ducts.

Dalle.

[Soundman2020]

I am thinking of using MDF rather than plasterboard because of the increased in density.

It is higer density, yes, by about 10% or so. However, it would take you a lot longer to do it with MDF, because you'd need to cut each and every piece with a circular saw or table saw, and then sand, route, file, or drill to take care of irregularities. Drywall is much easier to work with from that point of view: score with a sharp knife, and snap. Done! (Irregularities are also simple and fast to deal with.) In addition, drywall is usually quite a bit cheaper than MDF in most places.

So although you'd get the slight benefit of higher density, it would be much slower to do, and more expensive. I'd just go with plain old ordinary 16mm fire-rated drywall.

Thanks for the additional information on the windows – very helpful. I didn’t know about the need to maintain the density.

Yup! The entire isolation of your room is only as good as the isolation at the weakest point. If the wall is less dense where the windows are, then that's a weak point.

It works like this: the two "leaves" of the wall plus the air in between act as a tuned system. You tune it to a frequency that is at least one octave lower than the lowest note you need to isolate. You tune it by adjusting the surface density of the leaves, and the size of the gap in between. If there is some area of the wall where the surface density is lower, then that part of the wall will have a higher resonant frequency, thus reducing your isolation.

Any tips on where to where to find the calculations for the dimensions and air flows

Most places recommend around 8 "room changes per hour" for occupied spaces, but check your local code. You might be able to do it with 6. So figure out the volume of your room (cubic meters), multiply by six, and that's how much air you need to move through the room in an hour. Divide by sixty: that's how much you need to move in one minute. The general recommendation is to make sure that the air coming out the registers is moving slower than about 90 meters per minute (roughly 5.5 kph). The rest is simple geometry and simple math (hint: cross sectional are of the duct...)

I will just go with a standard air conditioner with the ventilation ducts.

Standard split-system! Not the "through-the-window" type...

- Stuart -