Double Garage Shed Conversion

Hi there! I’m looking to convert an existing garage shed in suburban Sydney into a rehearsal/studio space. I’ve done a fair bit of research on this forum and read Rod’s book and would greatly appreciate any advice you can offer! I’m currently in the design phase, looking to start work by the end of the year, and just trying to come up with a good floorplan and researching how to achieve an appropriate level of isolation. THE GOAL I want a room where I can play my drums without annoying the neighbours, and where I can jam, record and mix with my band. Later down the track, I hope to be able to provide a separate space where my wife can teach piano, and which could also function as a small live room/booth. My current band plays rockabilly roots, with double bass, acoustic guitar, electric guitar and just a snare drum, so it’s not too loud. Occasionally though I like to jam with some other buddies who are into reggae and death metal, so at times it will get bass heavy in there! I gave the drums a good belting and measured the SPL from about 3 feet away and got 105db on an A-weighted SPL meter. I also measured outside the shed from about 20 feet away and measured 75db. I’m hoping to get that down to a more neighbour friendly level, but not exactly sure what I should be aiming for. Q: At a guess I’d say I need to bring the outside volume down to about 40 - 50dB, so I will need 55 - 65db Transmission Loss. Does that sound about correct? THE EXISTING SHED The current shed rests on a concrete slab measuring 6 x 5.4m (20 x 18ft), and varies from 300mm – 600mm thick. The slab is adjacent to an existing concrete driveway, which I’m considering extending onto to build the piano booth later. I’m not entirely sure if the two slabs are separate or not, but they seem to be touching at the least. The wall frames are made of 45 x 70mm wooden studs, spaced 550mm apart, with what appears to be a double-stud in each corner. There is a gabled roof measuring 2.4m high at the walls to 3.3m in the centre. The rafters are 45 x 90mm, and the four ceiling joists are 45 x 145mm. Wall and roof covering is a single layer of colourbond steel. There are two roller doors, one regular door and two small windows. The house has three phase power connected which I’m assuming will be beneficial? The neighbours living room is just a couple of metres away over the fence. BUDGET My wife and I recently spent almost every cent we had to buy this little house, so the budget is tight. If I can get away with AUD $10K over a year or two then I will be very happy! However I want to do it right, and if I have to spend a bit more to get the result then I will, it’ll just take me longer to finish… I already have a pile of 10mm Soundchek Gyprock which a builder friend salvaged from a shop re-fit for me. I’ve got about 250 square metres of the stuff. I understand that 10mm is not recommended, but being as it hasn’t cost me anything it would be great if I could make use of it! Q: If I used Green Glue between two or even three layers of the 10mm Soundchek on the outer leaf, would that achieve a reasonable mass and reduce the undesirable resonances associated with such thin material? Perhaps it would be better to combine one layer of 10mm with one layer of 16mm on each leaf (with Green Glue)? I have a cousin who is a plasterer and a brother who is a carpenter, so I’ll have a bit of assistance. I’m confident with the walls but I wouldn’t touch any roof work myself personally. CONSTRUCTION & METERIALS The plan is to go with a single room two-leaf Mass-Spring-Mass construction, with splayed walls and ceiling to create a Reflection Free Zone. I plan on building in several phases as I save the money over a couple of years. Phase 1: Beef up and seal the current frame-work with as much gyprock as it can support. I would like to use two layers of the 10mm Soundchek that I already have, or one layer of Soundchek and one layer of 16mm Frychek. All layers will be dampened with Green Glue. This should at least give me a small amount of much needed isolation for the moment! I suspect that the current framework is a bit on the light side, so I may not be able to put as much mass on there as I would like. Q: Is it possible to strengthen the existing framework without tearing it all down? Perhaps adding some extra 45x100mm support studs for the ceiling joists? I would also like to remove the current colourbond cladding on the outside walls and replace it with a flat surface, as both my wife and I like to paint and want to decorate the outside of the studio with a mural. Q: I have no idea what type of material to use for the outer layer. Some sort of fibre cement board, plywood or render? Any suggestions? I’ll get rid of the two roller doors and make the regular door a bit bigger for lugging gear in & out. My wife has requested that I retain the window in the rear wall as it has quite a nice view, which we don’t get to enjoy from the house because the shed is in the way! I’m happy to include this window, and was thinking perhaps I could knock up some sort of insulated “insert” for when I’m mixing, to deaden any reflections off the glass… Phase 2: Build second leaf frame-work from 45x100mm studs, 50mm in from the first leaf and add 2 layers of 16mm Frychek. Stuff with insulation in between. I’m considering constructing the front and back wall inside-out to retain more room length, while the side walls will be regular construction. I’m struggling to work out how the reduced airgap of the inside-out walls will affect the resonant frequency. I guess there’s a compromise to be made between space/room ratios and better low frequency isolation? I’m hoping to move the joists up to 2.8 high, but that’s yet to be verified by a structural engineer. If it can’t be done, I thought perhaps I could “build around” the current joists. Has anyone here had experience doing this sort of thing? Phase 3: Extend 2.5m onto the driveway to incorporate a piano/iso booth approx. 2x4.5m. Build a door with a window back into the main room. In order to avoid a three leaf wall in between the two rooms, I thought I would extend the outer leaf to encompass the new space, then just knock some of gyprock out of the existing outer leaf wall, before building the inner leaf of the new room. That would leave the original frame running through the airgap of the adjoining wall, but as long as it doesn’t touch the new inner leaf it should still function as a two leaf system right? LAYOUT I’m quite content to stick with a single multipurpose room, as I’d rather have one half decent sounding room than two small sucky ones! Later when I build the piano room I’ll at least have the option of sticking a singer or guitar cabinet in there if needed. Most of the time though it’s just going to be me practicing, writing, and tooling around on my own demo recordings… Assuming a gap between frames of 50mm, the maximum dimensions I can achieve is 5696 x 4936, and at the moment I’m working on the assumption that I can attain a ceiling height of 2800mm down the middle. When I plug these dimensions into Bob Golds mode calculator it reveals several serious modes between 33.5 - 86.2hz, and also fails one of the three BBC critical listening tests. The best ratios I can fit into this room without losing too much space appears to be Louden’s Tertiary at 2700 x 4050 x 5670. It seems that I can also widen the room up to about 4500 without too many negative consequences appearing, so I might consider that also. Q: If I did go with the smaller dimension, I wondered if its possible to utilize some the airgap created by the splayed walls as storage. Does anyone know of a good way to achieve this without compromising the M-S-M structure? I’ll splay the side walls 6 degrees each and float a hard backed ceiling cloud at an angle above the mix position. With the splayed walls I’m measuring the dimensions from the midpoint. I’m working on my Sketchup model but am having a very difficult time of it, so in the meantime here’s some rough plans using floorplanner… So, that’s about where I’m at right now! I feel pretty good about most of the planning to this stage, and am hoping to start on Phase 1 within the next few months. Some pics of the existing shed are attached.. Once again I thank everyone in advance for input and advice you can offer, I truly feel that this forum is the best thing on the internet! Cheers, Graeme

Hi Graeme and welcome to the forum! So sorry that nobody replied to your initial post here: :oops: It seems ot have fallen through the cracks, and I only just noticed it, more or less by accident. If that happens again, and your thread doesn't get an answer in a few days, then feel free to "bump" it.

I want a room where I can play my drums without annoying the neighbours, and where I can jam, record and mix with my band. ... at a guess I’d say I need to bring the outside volume down to about 40 - 50dB, so I will need 55 - 65db Transmission Loss. Does that sound about correct?

That sounds about right, but 65 dB is a tall order. It can be done, but it ain't easy....

I gave the drums a good belting and measured the SPL from about 3 feet away and got 105db on an A-weighted SPL meter.

Essentially that means that you have no isolation at all right now. However, you should be measuring on "C" weighting, not "A". "A" is no use for measuring full-spectrum transmission loss, since it does not consider low frequencies. The curve rolls off steeply at the low end. "C" also rolls off, but much less steeply, and more closely resembles the perception of the human ear.

THE EXISTING SHED...

... is basically not giving you any usable isolation at all: maybe 10 to 20 dB, from your tests.

I already have a pile of 10mm Soundchek Gyprock which a builder friend salvaged from a shop re-fit for me.

You need to somehow convert that to 15mm (or 16mm, if possible) somehow. Maybe do a swap with someone? Or sell it and use the money to buy the thicker stuff? Unfortunately, 10mm is too thin for good studio isolation. Too flexible, mass too low, not so great resonant characteristics, etc. Also, looking at your photo of that stack of drywall, it seems like you have every pair of sheets attached to each other with thin wood strips. What's with that? It wouldn't be any use to you like that, even if it was 16mm.

Phase 1: Beef up and seal the current frame-work with as much gyprock as it can support.

You could do that, but frankly I wouldn't bother: Too much work and hassle. I would suggest rather going with the dreaded "three-leaf" route: Leave what you have there as the outer-leaf, as is, no changes, since it is not much use at all acoustically, then build a two-leaf structure inside it,with a lot of mass on the "middle" leaf. Yes, that would waste some of the space that you have, but it would greatly simplify the build.

I would also like to remove the current colourbond cladding on the outside walls and replace it with a flat surface, as both my wife and I like to paint and want to decorate the outside of the studio with a mural.

Ahhh! Well, that's different then! In that case, you could just use something very massive for that new outer sheathing, such as thick OSB or plywood as the base layer with thick fiber-cement board as the outer later. That would get you lots of mass, plus the surface that yo want for your murals. And then just build a single leaf inside, for the actual studio.

I’m happy to include this window, and was thinking perhaps I could knock up some sort of insulated “insert” for when I’m mixing, to deaden any reflections off the glass…

Not necessary: the room can be designed such that it isn't needed. In any case, if you want to keep light coming in, then you'll need a matching piece of glass on your inner leaf. And if you want high isolation, you'll need to replace the existing glass with thick laminate glass.

Build second leaf frame-work from 45x100mm studs, 50mm in from the first leaf and add 2 layers of 16mm Frychek.

Did you check that the gap and mass are large enough to provide the frequency and isolation that you need?

I’m struggling to work out how the reduced airgap of the inside-out walls will affect the resonant frequency.

You need to use the equations for MSM resonance to calculate that:

I’m hoping to move the joists up to 2.8 high, but that’s yet to be verified by a structural engineer. If it can’t be done, I thought perhaps I could “build around” the current joists. Has anyone here had experience doing this sort of thing?

I did a place in LA last year where we did exactly that: put in a new very large ridge beam supported only at the ends, then replace the trusses one by one with stick-built trusses with higher cross bars. Allowed us to raise the inner-leaf ceiling a couple of feet, and fit in the HVAC much better. IT can be done...

When I plug these dimensions into Bob Golds mode calculator

You show your room as being non-rectangular: therefore Bob's calculator won't produce accurate results. It only works for rectangles. However, you can plug in the average dimensions of the inner-leaf surfaces to get a rough idea of how it will behave.

it reveals several serious modes between 33.5 - 86.2hz,

I'm not seeing that! With the dimensions you gave, there are no issues at 33.5 Hz, nor at 86.2 Hz. The real issues are at 62 Hz, even more so at 69 Hz, where you have 4 modes all practically on top of each other, then at 76 Hz, and 93 Hz. Those are the issues under 100 Hz. I agree that the ratio is not good (the length is twice the height! :shock: ), but there are no modal issues at 33.5 or 86.2 Hz.

I wondered if its possible to utilize some the airgap created by the splayed walls as storage.

You are wasting a lot of room volume with those splayed walls. You only need to splay the front section of the side wall, from the mix position forwards. The rear does not need to be splayed.

Does anyone know of a good way to achieve this without compromising the M-S-M structure?

If you shrink the room enough, you can put a storage area down one side of it, but you still need to retain the MSM integrity.

I’ll splay the side walls 6 degrees each

6° is for flutter echo, but there are other ways of dealing with that. You did mention inside-out walls, so you wouldn't even have a flutter echo problem if you did that. However, you seem to be showing an RFZ design, which does need splayed walls at the front. But they will need to be angled a lot more than 6° to produce a true RFZ. So I'd suggest re-doing the inner-leaf as a proper RFZ with only the front part of the side walls splayed, and make your speaker soffits big enough to do the job properly, while re-positioning them to the locations where they should be. - Stuart -