piano teaching/recording studio - construction questions

Hi folks, So I've got a design somewhat finalized for converting/adding on to my detached garage to create a space for my wife to teach piano in, and for me to record/write/screw around in. I have a thread in the Design forum that goes into detail: My Design thread I'm going to present my construction questions one at a time. Ok here goes with Number One: In a nutshell, we're looking to add roughly 24x13' onto our 12x32' garage (see above link for details). My wife's teaching space would take up most of the new section. Because we'd be pouring a new slab for this section, I'm investigating doing an isolated slab a la Sharward's studio in leu of floating the floor. I'm starting to talk to contractors & my city's permits department, and I want to make sure and present it to them in such a way as to make things as smooth as possible. Specifically, I'd like to avoid having to hire an engineer. We'll see about that. :roll: I'm assuming that the building department is going scrutinize the foundation structure that bears the exterior walls. Here's my first best guess as to how one might do this: It seems to me that if we poured the outer "ring" (which will bear the exterior walls) retaining-wall-style with a somewhat-deep footing, then we could pour a standard slab inside of this, completely isolated from the outer foundation. I should mention that I will probably not be submitting drawings (my contractor will, but we haven't nailed a contractor down yet). I just want to come into this as educated as possible. So my questions: 1. If any of you has done the isolated-slab thing as new construction, how does my drawing jive with how yours ended up? Any permits issues? 2. What's the minimum space I can have between the two slabs (I want to get as much interior space as I can). 3. I've seen rigid insulation mentioned to span the gap between the slabs; are there other materials to use? (No problem with rigid insulation, just curious.) Let me know what you think - thanks! ---Devin

Beautiful illustration, Devin! 8) I'm honored to be an inspiration to you on this aspect of your plan. I hope it works out for you -- please don't blame me if it doesn't! :shock: ;-) My only "off the top of my head" recommendation would be to increase the depth of your "rigid insulation or ?" piece so that it is as deep as your footing. Others may disagree. Take my point of view with a big fat grain of salt. Make that two grains. ;-) --Keith :mrgreen:

sharward wrote:

Beautiful illustration, Devin!

Why thanks.

sharward wrote:

My only "off the top of my head" recommendation would be to increase the depth of your "rigid insulation or ?" piece so that it is as deep as your footing.

I see what you mean, and it makes sense to me. I'll probably leave details like that up to the contractor, though. What will you be using to span your gap? & how big will the gap be?

I don't know yet! :oops: I know, I know -- you wouldn't expect that from Mr. Plans Everything Down To the Nitty Gritty Guy, huh? :lol:

Only thing I see is I've never known a building official to allow gravel under a wall footing; maybe if it's compacted to surrounding earth characteristics, but generally they want solid, undisturbed earth or compacted and tested for all footings. The rest of the slab can have gravel as shown. Rigid insulation (EPS) is what to use, 1" thick minimum. Keep in mind when deciding on space taken up by walls, that this will also affect isolation by changing the air space between inner and outer masses. If you post desired dimensions and materials, I can give you an approximate isolation value... Steve

knightfly wrote:

Only thing I see is I've never known a building official to allow gravel under a wall footing; maybe if it's compacted to surrounding earth characteristics, but generally they want solid, undisturbed earth or compacted and tested for all footings.

Thanks for catching that, Steve :oops: - I'm getting a grasp on the details as I go. I will be working with a contractor for the major structural construction so I'll have additional help when finalizing this stuff.

knightfly wrote:

Rigid insulation (EPS) is what to use, 1" thick minimum. Keep in mind when deciding on space taken up by walls, that this will also affect isolation by changing the air space between inner and outer masses. If you post desired dimensions and materials, I can give you an approximate isolation value... Steve

I'd appreciate that - my best guess right now would be (for the new construction): Sorry for the ugly picture - I'm posting this from a tent in New Orleans (the Portland Water Bureau has sent a team to help rebuild the water system - I'll be here another 3 weeks) and MS Paint is my only option. Assuming a 1" gap between slabs, lets say that the gap between the two sets of framing (the pink above) would be around 2", so assuming no "beef-up" between the studs on the outside, that would be approx. 9" of air gap. Let me know if you need more to go on, and thanks! :D ---Devin

Done properly, that wall construction should run around STC 71 with a low end TL of about 38 dB @ 50 hZ, and a m-a-m resonance of around 38 hZ - not quite death metal drum isolation, but should do quite well for piano and anything BUT drums... Steve BTW, I completely ignored the outer siding since I wasn't sure what you intended to use; if it's tight against the two layers of OSB and heavy(like cement board), you'd be looking at 3 or 4 dB better on each number, with a m-a-m resonance of around 31 hZ.

I would imagine that increasing the depth of the gap from 9" to about 12" would pay off well.

knightfly wrote:

Done properly, that wall construction should run around STC 71 with a low end TL of about 38 dB @ 50 hZ, and a m-a-m resonance of around 38 hZ - not quite death metal drum isolation, but should do quite well for piano and anything BUT drums... Steve

That will probably suit my purposes. Is the floor the weakest link in your low end TL calculation? I'm wondering if it would be worth it to beef up the outer walls (gypboard between the studs) or add another layer and get a little better figure. I think that occasionally I'll be wanting to have fairly loud funk or rock rehearsals in there in the evening. No death metal, but rock & funk drums played at a strong "professional" level.

knightfly wrote:

BTW, I completely ignored the outer siding since I wasn't sure what you intended to use; if it's tight against the two layers of OSB and heavy(like cement board), you'd be looking at 3 or 4 dB better on each number, with a m-a-m resonance of around 31 hZ.

This brings up another question for me - I was kicking around the idea of using wide hardi-plank for siding, lapped to match the existing cedar shake siding that will remain on the existing structure. This would introduce air gaps where the planks lap, which probably doesn't count as "tight against the OSB". Do you think this might even diminish TL (introduce another leaf)? Is there a way to fill those gaps suitably?

sharward wrote:

I would imagine that increasing the depth of the gap from 9" to about 12" would pay off well.

That's something that's still up in the air for me - I'd like to maximize square footage inside, so I'll have to decide if the extra TL would be worth giving up that space.

If you're talking about the isolated slab, then the floor isn't likely to be the weak link; especially if you build an inner ceilng frame and keep the construction fully room-in-room. If you want better low end TL, and you're building NEW construction, it's much easier to use an added layer of sheathing (OSB, 3/4") to the outside of the stud frame than it is to cut and paste chunks of gypsum between studs. Yes, the tapered gaps caused by shingling the hardiplank would constitute an air gap, but I've no way of calculating just what the damage would be; it's a fairly narrow gap even at its widest point, so would have a fairly high resonant frequency - likely around 220-280 hZ. An added 3/4" layer of OSB on the outside frame should more than compensate for that, and a wider air gap as Keith mentioned would improve low end TL by around 4-5 dB. If you list a couple of wall scenarios, each with no more than two differing materials on each leaf, I can re-do the Wild-Assed Guess. I'm not aware of any material that would work well to fill the gaps behind the hardiplank - fiber insulation is still effectively air, spray foam is too hard to control, and you'll need a house wrap in there somewhere. Also, the effect of the extra mass will only be where it's the THINNEST, so it's probably better to just realize the possible negatives and compensate for them in order to get the look you're after. Keep in mind that field STC is ALWAYS less than computed by at least a couple dB, and that's if you're CAREFUL in every detail. As to maximizing square footage - understood. But keep in mind that we're talking about 3" thicker walls - if that makes the difference between actually being able to USE the space and NOT, then that also needs to be factored in... Steve

Hi everyone, I haven't checked in in quite a while :oops:, but believe it or not, the thing is getting built. The contractors have been done with their part of the job for a few months, and I'm slowly chipping away at it on my own when I have time, which is not a whole lot. Our goal is to have Monica teaching out there in the Fall, but we're not freaking out about the deadline. Here's what's done so far: Foundation/isolated slab poured "Outer" shell framed up, sheathed & sided, front & back door installed Roofed "Inner" framing for piano room done Framing for bathroom & waiting room done Drywall (3 layers 5/8") hung on underside of outer rafters (see this post as to why) Rough plumbing done Electrical service revamped So, here are some pictures of highlights (CLICK HERE for all of the pics). I'll post 4 at a time.

Moving along...

more...

more...

sandman!!! Wow, you've been really busy!! 8) I looked at all the pictures in the gallery on your Web site. I have some questions... What was the rationale salvaging the front face of the garage? You guys did a really nice job with the blending, reducing the doorway opening. I just wonder why you didn't decide to bulldoze the whole thing and start from scratch. Was there really a cost savings there? Or were there other factors -- e.g., was it easier to get the project approved from city planners by leaving some of the old structure intact? :roll: Also, I see the new rafters, and I'm wondering if you're planning to hang drywall on the bottom of that... If so, you've got yourself a three leaf system and I just want to be sure you have accounted for that less-than-ideal situation with additional mass. Ohhhhh, wait -- I just followed your link to this thread where that was thoroughly discussed! Excellent! 8) Awesome work! 8) Please keep this thread updated with progress -- this is a really exciting project, and I remember like it was yesterday when you first came here to talk about your ideas! :twisted: I'm really glad for you that everything is coming together so well and that you were able to overcome the bureaucratic obstacles to building this dream of yours. :D --Keith :mrgreen:

sharward wrote:

I have some questions... What was the rationale salvaging the front face of the garage? You guys did a really nice job with the blending, reducing the doorway opening. I just wonder why you didn't decide to bulldoze the whole thing and start from scratch. Was there really a cost savings there? Or were there other factors -- e.g., was it easier to get the project approved from city planners by leaving some of the old structure intact? :roll:

Exactly! The north wall is right on the property line. I had to have the setback requirement adjusted for my case (normally they require a 5' setback). They also required that the north wall be a 1-hour firewall. If I had torn the whole thing down and started from scratch, there's no way they would have let me build on the property line. Basically, all we left was that front part (plus the north wall framing) - and we thought it would be cool to preserve the character of the original garage (which matches the house), at least from the front. It worked out pretty well - we have a nice wood door installed now, & it looks even better. I'm looking forward to painting it to take care of the "patchwork" look it has now.

Also, I see the new rafters, and I'm wondering if you're planning to hang drywall on the bottom of that... If so, you've got yourself a three leaf system and I just want to be sure you have accounted for that less-than-ideal situation with additional mass. Ohhhhh, wait -- I just followed your link to this thread where that was thoroughly discussed! Excellent! 8)

Yep, that was a dilemma for a bit...

Awesome work! 8) Please keep this thread updated with progress -- this is a really exciting project, and I remember like it was yesterday when you first came here to talk about your ideas! :twisted: I'm really glad for you that everything is coming together so well and that you were able to overcome the bureaucratic obstacles to building this dream of yours. :D --Keith :mrgreen:

I'll do my best; I'm finding that having an infant around...well...takes up a lot of your free time! :P Really, I appreciate everyone's input & encouragement - I'll keep updating! I need to take some more pics (these are already months old). It seems that the comments I put with the photos when I uploaded them aren't showing up for some reason...I think they're pretty self-explanatory though. If anyone has questions, let me know...