On Purpose Productions detached garage studio

[onpurposeproductions]

Actually.......I've been planning on constructing my new inner walls 16" on center. Should be aiming for 24"?

I've been assuming that 24"OC wouldn't be sufficient for two layers of 5/8" drywall on walls? Maybe with bracing?

[Soundman2020]

Greg, I may be wrong, but I get the impression that you are confusing your inner leaf and outer leaf somehow. And in any event, the construction does not need to be consistent all around: it just needs to provide the same level of isolation all around.

Since the existing bottom chords of the truss have nothing on them right now they'll need a layer of OSB plus two layers of drywall to match the walls.

The underside of the roof joists is where you hang your inner leaf, not your outer leaf. The roof itself is your outer leaf.

So you are saying that your outer leaf has some kind of siding on the outside, then OSB, then a coupe of layers of drywall that I imagine you are inserting between the studs to beef up the outer leaf. Correct? So that's your outer leaf wall. Your inner leaf wall will be, I imagine, a set of studs with a couple of layers of drywall?

Since the existing bottom chords of the truss have nothing on them right now they'll need a layer of OSB plus two layers of drywall to match the walls.

The underside of the roof joists is where you hang your inner leaf, not your outer leaf. The roof itself is your outer leaf.

Now, since your ceiling is part of your inner leaf, not part of your outer leaf, if you really did want to retain consistency then your ceiling should have just a coupe of layers of drywall and no OSB, just like your inner-leaf walls.

If this is not the way you are building it, then please could you point me at your thread so I can see your sketchup model of how you actually are building it (ot just post a quick and rough SketchUp diagram of your wall construction detail), since maybe I'm just misunderstanding what you are explaining.

But apart from that, there really is no need match to construction materials, just for the sake of consistency. What matters is that the isolation level is consistent all the way around, not that the construction materials are the same. So you could have one brick wall, one lead-sheet wall, one steel plate wall, and one sheetrock wall, and that would be just fine, as long as they are all built to provide the same amount of isolation. That's why you want to your window glass to be roughly the right thickness to match the mass of the rest of your wall, so that it is not too much of a weak point.


- Stuart -

[plus6vu]

Hey Scott, thanks for posting. Do you have a design or build thread going yet?

You mean you're cutting the OSB to fit in between the stud cavities, right? This would certainly provide at least some bracing between the joists and prevent them from warping, which is really good.

I am pretty sure that the blocking between studs does spread the load and therefore adds structural strength, I'd think you should be able to do that rather than adding an additional beam below the ceiling as you mentioned.

But of course, this is the very question I'm asking. Anyone have an answer?

No I don't have a build thread going. This is a slow moving project and I hadn't found the forum until after I had started the construction. Just in time for some things, a little too late for others, but it's going well so far.

Actually, I am not talking about blocking between the studs, but just putting it over the studs as one would a normal install.

More below
Scott

[plus6vu]

Why would you want a stiffer ceiling? That will increase the resonant frequency, thus reducing isolation at the low end.

For the first two rooms, I was wanting a little more structural stiffness in case I wanted to use that space for light storage. In this (other) particular room, given that the 2x4's are such a long span, I was thinking that the osb/plywood would give it more structural strength to hold the weight of the ceiling without ripping down the 2x4's and replacing them with something else - which I will do if it is neccesary.

Well, if it's just personal choice, then that's what it is! But it isn't acoustically valid reasoning. It will make the ceiling thicker and more expensive to build for the same mass, or less massive for the same cost, and with reduced acoustic isolation either way. But if you prefer it that way, then that's fine, I guess. As long as you understand what you are sacrificing, and don't mind the limitations.

That's why I specified that it was personal choice. The walls are a little more expensive and only slightly thicker. It's pretty quiet where I am, so maximum isolation is not a huge issue.

That's why the experts here recommend drywall! Building a wall (or ceiling) with 24"OC studs and drywall brings down the resonant frequency about as much as you can without spending huge amounts of money on exotic materials, such as lead for example. Stiffening the wall by putting the studs closer together or using less dense but thicker and more rigid materials, will raise the resonant frequency of the wall assembly, thus also raising the frequency at which you get minimum isolation, and probably bringing it into an area where you don't want it.

I actually lined out the plan here before using osb on the walls and neither Knightfly nor Sharward mentioned any reason not to use osb instead of sheetrock in their replies to me. If they had, I would have done differently.

You WANT the wall to be resilient, and you WANT density, and you WANT mass. There are good solid acoustic reasons for the recommendations made by the experts here.

I am aware of that. And, that's why I asked several years ago before I started covering the walls.

Don't get me wrong: what you are doing with plywood or OSB will still work for isolation, to a certain extent: It will just be less effective, or cost more. Or both. If you don't need maximum effectiveness, and don't mind spending more money than you need to, then personal choice wins out over acoustic science! - Stuart -

I always appreciate someone setting me straight, but given what I was told (or not told) a few years ago, I went with the information I had at the time. BTW, the OSB is 3/4 behind 5/8 drywall. They are very close to the same mass. As for resiliency, if that were as big of a factor, I wish someone had mentioned it when we discussed it several years ago. And the cost - this is a small studio, the difference in cost is not that much.

Now I still have one more room to go, the one I'll be tracking in. So, I still have time to make adjustments. It's only studs right now. Does anyone else have an opinion against using osb instead of drywall?

Thanks all!
Scott

[onpurposeproductions]

Now I still have one more room to go, the one I'll be tracking in. So, I still have time to make adjustments. It's only studs right now. Does anyone else have an opinion against using osb instead of drywall?

It of course depends on your objectives. Drywall has a higher density than the same thickness of OSB. Drywall is around 700kg/m3. From what I've read the density of OSB can vary depending on the type of wood that's used. In a quick search I found these two sources - one says 640kg/m3, the other 600kg/m3;

http://www.canply.org/english/products/ ... on_all.htm
http://alcor.concordia.ca/~raojw/crd/es ... 00129.html

640kg/m3 is not bad considering OSB is usually FAR cheaper than drywall. So if cost is a bigger factor.......

[onpurposeproductions]

Greg, I may be wrong, but I get the impression that you are confusing your inner leaf and outer leaf somehow.

I initially was planning on making my sloped ceiling the outer leaf but because of ventilation requirements went with a suggestion from xSpace. Here's where it was discussed on page 1 of this thread;

http://www.johnlsayers.com/phpBB2/viewt ... 85&start=0

I put the following diagram together for a contractor while getting a quote. I've adjusted it to show what the plan is. Yes, there is technically three leafs but its a necessary reality. The attic will be used to store the HRV and associated ducting and it will also allow the attic to vent properly as designed. I did look at an unvented roof design that is allowed by code where you spray foam the entire attic space but decided against this.

[petrovinksy]

Backer Rod - 2.3 cents per foot (regular price)
Drywall - 20% promotional discount from Lowe's ($13.54 per sheet)
Caulking - 10% bulk order discount ($4.91 per 850ml tube)



Just wondering where you got the backer rod from?? Im in hamilton. i can't find it anywhere near that price.

[onpurposeproductions]

Backer Rod - 2.3 cents per foot (regular price)
Drywall - 20% promotional discount from Lowe's ($13.54 per sheet)
Caulking - 10% bulk order discount ($4.91 per 850ml tube)



Just wondering where you got the backer rod from?? Im in hamilton. i can't find it anywhere near that price.

He Petrovinksy - Yeah, this is THE source for backer rod in southern Ontario as far as I'm concerned. The 3/8" comes in a box of 2100' but I think you can buy smaller amounts if needed.

I got it from Construction Distribution & Supply, 760 Dundas St. East in Mississauga. They have an indiscreet entrance at the back of the building with a small contractors desk inside. They had all sorts of sizes and types so know what to ask for when you go.

They've got an online store where you can browse what they carry here;

http://www.constructiondepot.com/main/s ... S(Ontario)

[petrovinksy]

thank you very much.

[xSpace]

I just wanted to say that there is not an instance where you would have "0 psf" live load. Also, you cannot do addition subtraction or division, etc., on live and dead load.

And, as always, 2X4 is just a bad idea unless you are spanning only short distances.

[onpurposeproductions]

I just wanted to say that there is not an instance where you would have "0 psf" live load. Also, you cannot do addition subtraction or division, etc., on live and dead load.

And, as always, 2X4 is just a bad idea unless you are spanning only short distances.

Hi xSpace,

Thanks a lot for your input. I really do appreciate it. This whole process is feeling overwhelming just now Just when I think I have a good understanding of something I realize I don't have a clue.

Would I be right in guessing that the reason you could never have a 0 psf live load is because you could always mount something on the finish side of the ceiling (something temporary)?

And live and dead loads - they can't be added/subtracted/divided because they are always independent considerations?

2x4 joists always being a bad idea I'm having some trouble with - but I do realize I'm ignorant here. Is it reasonable to assume that doubling up every joist (laminating) should add strength and theoretically increase span capabilities? What about laminated joists plus blocking between joists?

That headroom is just so precious. I'm estimating that with 2x4 joists I would end up with a finished height of approx. 7' 7" (the unknown is how much I'll lose when leveling the Dricore subfloor). 2x6s would then take me down to 7'5". I don't want to be unsafe (and in fact the building inspector certainly won't let me) but I do want to find a solution if there is one.

[xSpace]

The guys that interpret code use manuals and reference books that have been developed for typical construction materials in typical building scenarios.

Using the small sampling of material that I have available to me, the first table for spanning 2 X4 13-3" on 12" centers does not even get that high. It stops at 11 feet 3 inches. That would be using a deflection of 240, Live load=20 / Dead load=10 with a required bending design in psi at 1,864! This is not clear pine or even lodgepole to have this kind of stiffness.

The next available table shows a dead load of 5 pounds, it's not even worth looking into.

Your dead load starts at 6.4 pounds a square foot, 2 layers of 5/8" rock, insulation and the weight of the 2X4 included. There may be other considerations for your weight values not known to me right now.

So anything you do with 2X4 just makes it more difficult for you, harder on the officials and not guaranteed to even pass or stay stable for ten years especially without historical reference to use in the evaluation.

Your experience may be different, but consider how the air is going to act in this build. If it does the job you want and becomes a spring, isn't this a live load? How much, I do not know, but if a wall gets sudden pressure(like the closing of doors)applied to one side it is sure to deform into the cavity and move the air that is going to in turn apply pressure to the backside of another panel of the wall/ceiling.

As an aside, in California a 15 psf live load is the least amount that can even be considered for any construction of any type. This could be something that may be applied to your build in Canada, if they have adopted a minimum.

[onpurposeproductions]

Using the small sampling of material that I have available to me, the first table for spanning 2 X4 13-3" on 12" centers does not even get that high. It stops at 11 feet 3 inches. That would be using a deflection of 240, Live load=20 / Dead load=10 with a required bending design in psi at 1,864!

But this calculation isn't considering doubling up the studs (which I've been calling laminating but I've learned is commonly called sistering). There certainly seems to be differing opinions out there about how much strength joist sistering provides, but from what I've read it will certainly reduce the amount of deflection and effectively provide greater strength to the joist.

So anything you do with 2X4 just makes it more difficult for you, harder on the officials and not guaranteed to even pass or stay stable for ten years especially without historical reference to use in the evaluation.

I would certainly discuss everything with the inspector before moving ahead. If he didn't like the sound of things I wouldn't proceed. Perhaps I just need to look at 2x6s for the control room and 2x4s in the live room.....

I need to find some hard data on the effects of joist sistering.

[Soundman2020]

but I do want to find a solution if there is one.

Did you consider the possibility of using resilient channel on the existing attic joists, instead of putting new joists on top of your inner walls? It would not be optimal, of course, but it would work. Have you checked if those joists can take any additional load? If not, could you replace those with larger joists?

The reason I suggest the above approach, is because of your head-room issue. If you can use the existing attic joists, or replace them with larger ones, then you gain several inches of head room, compared to your existing design.

And I think you are forgetting something: Your head room is going to be substantially less that what you mentioned, since you still need to put all of your acoustic treatment on the ceiling. I don't see that in your diagram, and that is going to take another several inches off your height...

A third option would be to continue on your current path, but heed Brien's wise advice and use 2x6 (or whatever it turns out to be), but build the ceiling inside-out, so that you can use the space between the joists for your acoustic treatment instead of having to hang it below the joists. That way, at least you can be certain that the bottom edge of the new joists is your final ceiling height, and you don't need to allow for the thickness of the drywall and also your ceiling treatment.


- Stuart -

[onpurposeproductions]

Hey Stuart - thanks for the suggestions.

Did you consider the possibility of using resilient channel on the existing attic joists, instead of putting new joists on top of your inner walls? It would not be optimal, of course, but it would work.

I think that would be far weaker in terms of isolation even if I could add a LOT of mass up there.

Have you checked if those joists can take any additional load? If not, could you replace those with larger joists?

The existing ceiling joists are part of the truss. I am still trying to track down who designed/built the truss to determine its load bearing ability, but I am fairly certain that it was only designed with a minimum load in mind. I intend to get either a truss designer's input or a structural engineer's input on how to properly strengthen it to bear what I currently intend to put up there. But I don't think its a wise idea to remove or replace members of the truss - I would add to it.

And I think you are forgetting something: Your head room is going to be substantially less that what you mentioned, since you still need to put all of your acoustic treatment on the ceiling. I don't see that in your diagram, and that is going to take another several inches off your height...

Sure, but there are always options regarding types of treatment and placement, but once a ceiling is at a certain level you're not getting any more height.

A third option would be to continue on your current path, but heed Brien's wise advice and use 2x6 (or whatever it turns out to be), but build the ceiling inside-out, so that you can use the space between the joists for your acoustic treatment instead of having to hang it below the joists. That way, at least you can be certain that the bottom edge of the new joists is your final ceiling height, and you don't need to allow for the thickness of the drywall and also your ceiling treatment.

You suggested this before and I gave it some thought then. It is a good way to save that 1.25" the drywall would take up but it would be a lot more work and I can't really imagine how to create a decent finished look?

More research.....but if I ultimately just need 2x6s then so be it.