New Guy with 24'x10'x7½' Garage with very close neighbours

Hi, I'm Alec. Been a lurker for far too long, so here's the deal. I have a 24x10x7½ Double Brick garage stuck on the side of my house. On the other side of the garage is a lane/walkway about 5' wide giving access to 6 houses running parallel with the long side of my garage. My neighbours gardens are a further 20' long before you're on their back doorstep. So I've got 25' between my outside garage wall and my neighbours back door entrances to their houses. I'm thinking double stud wall on the 3 outfacing garage walls and a single stud on the wall joining the house as there's a staircase and a utility room on the otherside (no main living/dining/bedrooms). The garage roof is arched 7' in the centre of the 24' wall, so I'm thinking most of that area can be sound treated to leave me my 7½' headroom below (still not a lot if I want to float a floor, I know) I'll be taking away the tilt & push garage door and double bricking the entrance. That only leaves me one way in and out via a 30" door on the back of the garage. I've attatched a pic of a rough design. I haven't included any acoustic treatment, basicaly I just want to know if this will work without pissing off the neighbours if I do it correctly. All suggestions would be greatly welcome, thanks Alec.

Well John designed this for what looks like a perfect fit.

that would only give me 9' front to back in the control room. Plus I have drummers carrying their kit through the control room , I might go with this...

"I'm thinking double stud wall on the 3 outfacing garage walls " - Not a good plan. You want best isolation you can get without losing a lot of space, right? You should read through this thread - http://johnlsayers.com/phpBB2/viewtopic.php?t=598 And then, see if you can tell me why putting two more walls inside your double brick walls is a near total waste of time, space, and money. (Not a gag, and I'm not being a smart-ass, trust me) You said you'd been lurking, but you may have missed some vital info in that thread... Steve

I read the entire post. Looks like the inside out wall design would be better for my limited space. I'm working on a new layout without the vocal booth, a 7' x 9' drum/live room and a 13#' x 9' control room. With a floating floor I should still have about 6'9 headroom. If anyone wants to suggest anything different my ears are open. Thanks again, Alec.

Whether you go Inside Out or Upside down, one of the points I had hoped you'd find was that you don't want more than ONE air space with TWO centers of mass, one on each side of the air space (insulation counts as air) between any two areas you're trying to isolate. More usually = LESS. IF your double brick walls are SOLID (no weep holes at the base) then you may be able to use only ONE layer of gypsum spaced off the walls for your second leaf - this would give within 1-2 dB of the same isolation as more layers (the bricks help) but with more "panel trap" effect - if you set your inner leaf spacing away from the bricks you could "tune" this extra trapping to a potential room mode problem frequency... Steve

That went straight over my head. My understanding was, for best sound proofing results I needed to build a room within the existing room (in this case my garage) and the inner room should be built on a floating floor and no part of the inner room should touch the outer. So I take it I MUST leave an air gap between the inner room and the garage. If you're then telling me that insulation counts as air and I should only have ONE air space in my construction, then I can't have any insulation on my inner wall? That's crazy! This is what I intended (after reading the thread you kindly pointed out)....

Sorry, I neglected to mention that insulation or air WITHOUT another mass doesn't matter from a soundproofing standpoint - your diagram is a proper double-leaf wall - the bricks being the outer mass, the insulation/air inside that is the ONLY air space that matters much, then the double layer of drywall is your SECOND leaf; inside that is just acoustic treatment, which might have a small detremental effect on sound proofing but not much. It's only when you SEAL things up reasonably tight (not allowing the air to escape quickly enough) that a mass makes much of a difference in isolation. Your drawing might cause a slight loss of Transmission Loss at the frequency of the slat resonator you've shown, but pretty negligible. Realistically, you'd probably see more loss at doors/windows so it wouldn't be even noticeable. I hope that cleared things up... Steve

knightfly wrote:

Your drawing might cause a slight loss of Transmission Loss at the frequency of the slat resonator you've shown, but pretty negligible. Realistically, you'd probably see more loss at doors/windows so it wouldn't be even noticeable. I hope that cleared things up... Steve

It won't be noticable? the noise outside the building won't be noticable to my neighbours? Or my attempts at soundproofing won't be noticable? I thought I had this pretty much wrapped up Steve. The elevating garage door if being removed and bricked up, double brick same as the rest of the garage. There's a small window in the rear next to the door which will also be removed and bricked up. The door at the rear is a good quality solid wood door on a very tight fitting seal. I also intend to give the full inside a skim of plaster to fill in any cracks (not that there are any that I can see).

the double layer of drywall is your SECOND leaf; inside that is just acoustic treatment, which might have a small detremental effect on sound proofing but not much.

So should I do away with the timber slats and use RC and more Gypsum? then apply acoustic treatment? Alec.

I think you're reading too much into some of my comments - when I said "negligible" I meant that it could be ignored. Your drawing is the way you should do it. Outside mass (bricks) insulation/air, inside mass (2 layers drywall) Whatever you put inside that is for acoustic, NOT soundproofing, purposes. These are necessary, or you'll have a soundproofed CRAPPY sounding room. The fact that some types of acoustic treatment (such as slat absorbers) may have a dB or two of negative effect on overall soundproofing, cannot be helped. They are necessary. You didn't show on your drawing whether you intend to do ALL the walls with slat absorbers - that's not a good plan, you need more variety than that. Your brick walls should be enough of a barrier, along with the double sheet rock, that you won't have any sound leakage problems with your design. Short form: It's good, build it 8) ... Steve

ok Steve, thanks. What's my other option to slots if I'm not to have them all the same? I'll be honest, If everything on the inside of the gypsum is sound treatment and not sound proofing I don't think I trust this to stop the sound traveling to my neighbours 25' away If anyone wants to throw in a "if it was me I'd do it like this......" I could do with the reassurance. Alec.

Lemontree - your suggestion about rendering the inner brick wall will increase the STC of the brick wall. A standard house brick has an STC of 39 whereas a house brick rendered both sides (13mm (1/2") 1:1:6,Cement:Lime:Sand) has an STC of 45. With the inside out wall you have 3 options of treatment. 1 - rigid fibreglass with a cloth cover - High frequencies. 2 - slots - low mid frequencies - high frequency reflective. 3 - panels like Ethan's panel absorbers - low frequencies - also high frequency reflective. Thus you can cover the whole range without loosing additional floor space. cheers john

OK, John's got your acoustics going - here's some idea of what you can expect for sound proofing. I don't know what you expect, but either of these is a damn good wall. Your brick (especially rendered) is your FRIEND, and the two drywall/air just clinches the deal. Don't sweat it - BUILD it :lol: Steve

Steve & John, huge thanks to you both. With my wall plan in place I guess my next question would be the ceiling. the garage doesn't have a ceiling as such, just open wooden beems 7½' high. Above that in the centre of the garage the peek of the roof is a further 7' above the rafters and slopes down to meet the rafters on the front and back at the ends of the building. The roof is double sheeted 5 ply with roofing felt and heavy tiles (this thing was built to last). If I'm floating my ceiling on top of the walls on my floating floor should I treat the space above the ceiling? Or will this more layers and more air spaces reduce the STC? Thanks again, you guys are great Alec.

Glad to help - on the ceiling, though, we'd need to know how your roof is vented/sealed, etc, before suggesting a ceiling plan. You still need to stick to the Mass-air-mass idea of the walls for good isolation, so if your roof is vented it doesn't count. Most roofs ARE vented, so things dry out and don't rot. Check it out thoroughly; exact spacing and size of framing members, whether the rafters are part of engineered trusses, maybe even a digital pic or two (please size them no bigger than about 700 wide), and let us know... Steve

hello again Steve. I feel like I've covered more ground tonight than I have in the past year of dreaming. I know offhand the roof is held up by manufactured trusses, I think 5 across the 10' width of the garage, maybe six. I'm sure I seen a few airbrick above rafter height on the outside of the garage...it's gone 1am here and I'm not lookin for a flashlight to go check ;) Can't do digital pics. I don't remember the roof being sealed when it went on...I'm guessing I'll need to use that expanding foam stuff the double glazing firms use inside the loft area of the roof where it meets the walls...beyond that I really have no idea what direction I should be going in. Alec

Got out the tape measure today (was going from the original plans before) and realised some of my sizes were off. Length 25'3" Width 9'7" Height to roof trusses 7'6" height above trusses to roof peek 5'7" There are 2 airbrick (hollow with latticed fronts on the outside of the building) each the size of two house brick on top of each other about 10' up the wall above the roof rafters evenly spaced about 8' apart. The roof is made up of 6 identical manufactured trusses (see pic below) stepped across the 9'7" width of the garage. 6 trusses with 5 gaps, from the house side out the gaps are 24", 24", 24", 24", 16½". The beams used in the trusses measure 5"x1½" As previously posted, if I'm floating my ceiling on my inner walls and floating floor what do I do with this roof space? This seems to be my last obstacle on the design front. Once I know how to treat it I can start calculating the materials and a cost (oh no, the cost!) I'm now looking at room sizes of: Control room: w 8'6" x L 12" x H 6'8" Live/drum room: w 8'6" x L 8' x H 6'8 that still leaves me a 3'6 x 5' space at the back after taking the door into consideration to maybe add a vocal booth Alec

didn't realise that pic was so small. The sizes are 5'7 high and 25'3 long

" don't remember the roof being sealed when it went on...I'm guessing I'll need to use that expanding foam stuff the double glazing firms use inside the loft area of the roof where it meets the walls" - You definitely do NOT, repeat NOT, want to seal that roof area with expanding foam or ANYTHING else - it was vented like that intentionally so that the moisture that collects in your attic area from condensation, etc, gets a chance to DRY OUT from the air circulation - this is fine, and pretty much what I expected - however, I've been caught off guard by the unexpected a couple of times so I always ask rather than assume. All this means, is that you'll need TWO mass leaves for your ceiling separated by an air/insulation cavity - I'm on my way to another 12-hour day shift followed by 2 12-hour night shifts, so don't have time right now to lay out what you need to do for your ceiling - Please don't seal up those air bricks though, that would be a big mistake. I'll work on a couple ideas in the next couple days. Meantime, when you get the chance if you could check availability on materials such as drywall sheets in 1/2" and 5/8", and lightweight 25 gauge steel framing studs, at least 3-1/2" wide or more, that would help. Gotta run for now, let me know... Steve

the drywall is't a problem Steve, I live a few streets away from a building supplies company I've done a lot of business with in the past. Steel studs? I was thinking timber, or is the steel for the ceiling? I know you're workin man, I apreciate your time. Alec.

Actually, what I was thinking about is a couple layers of gypsum wallboard directly on your ceiling joists (the underside of the trusses) followed by some light gauge (25) 3-1/2" steel studs (gives aur/insulation space and FLEXIBLE mounting for the second round of wallboard layers) then 2 more layers of wallboard (1/2" and 5/8" ) - If you have access to Resilient Channel, you could use slightly heavier steel studs between your two leaves of gypsum, then put the Resilient channel on before the inner two layers of wallboard - that would let you leave your attic ventilated, and still give two leaves of mass with one air?insulation space between them. That would give best isolation with minimum headroom loss. In every case, your best sound proofing will be had with mass-air-mass construction - each center of mass should wrap completely around the space to be soundproofed, and NOT touch the other center of mass. Any sound should have to go through mass/air/mass to get in or out. Nothing more, nothing less. If you draw a plan for construction, you should always check to see if this rule is followed - simply pretend you're a sound, and you're trying to get from one room to the other, or from one room to outside, etc - in ALL cases, to escape you should have to get through mass, then air/insulation, then mass. If there's another barrier in the way, you will actually have LESS isolation than with just two. I tried to find time to do a drawing of the ceiling idea for you yesterday and today, but work has been 12 hours of non-stop hell on wheels lately. Hopefully in the next day or two... Steve

For the ceiling that is. What if I layed 2 layers of gypsum (staggering the seams) directly onto the roof truss beams on the underside, then used acoustic sealant (Caulk?) to seal this against my rendered walls. Then I use a ceiling design same as the walls underneath on top of my floating floor and walls but maybe use 3 layers of gypsum, or a layer of plywood sandwiched with 2 gypsum layers. That way my room (rooms...I'll be building 2 seperate floating rooms inside the garage) will stay detached. This still confuses me slightly though, as I'll have a ceiling of 3 layer Gypsum (MASS) insulation/air the 2 sheets of gypsum on the rafters (MASS) so that gives me my MASS/AIR/MASS ceiling and it's detatched from the main garage. BUT, above the rafters I still have another BIG airgap and more MASS consisting of the double sheeted 3ply, roofing felt and tiles that make up the roof? will this 3layer gypsum/ansulation/2ply gypsum give me a good enough STC rating? because anything that gets through that is gonna go floating fight out the 2 airbrick before it gets a chance to hit the roof. I'm sure there's a simple answer but it seems every time I try to think things through myself I end up digging a large unnecisary hole for myself. Alec.

Hi guys - may I butt in here. :) Alec that wall drawing you posted came from the SAE site. On the same page I describe a ceiling system that matches. What Steve has advised is totally correct - when you seal off the ceiling under your trusses that seal will go to the rendered brcik wall. The next question is how to create leaf 2 - your ceiling. Steve's suggested correctly that you can hang a second leaf off the first one using RC. In my plan I span the new ceiling from the new inner walls with the drywall on top and a treated 703 layer below - so you create your second leaf which is mechanically disconnected from the outer ceiling as well as treating the inner surface acoustically - just like the walls are doing. With a low ceiling like yours it's advisable to treat it totally with 703 as it is so close and parallel to your bright floor yet you maintain your high end brightness by using additional slots and panel absorbers on you walls. Not completely covered, maybe 50%. cheers john

Thanks John, that's cleared things up nicely. The blue existing ceiling in your drawing is the 2 layers of drywall I'll be fixing to the rafters of the roof trusses. Below that I'll have my isulation (703? or the UK equivalent), 2 more drywall layers on a wooden frame filled with more insulation for acoustic treatment. So I understand I'll get a better STC using RC between the rafters and the drywall I'll be sealing to the rendered walls, before floating my ceiling on my new walls. Rocket science! I love this forum Alec.

holy holy! I just worked out I need 28 sheets of 8'x4' drywall. Anyone know the Scottish word for Caulk?