5.1 Postproduction in Garage

Thanks for poitning that out steve. Partcile board hates water. And I hate to say it, but so does OSB. At least what I have used. Just like that article said, the product will improve, but is it there yet? I left a sheet of OSB on my front porch during the construction for 2 days during heavy rain, the junk was soft as particle board. I'd do the plywood first then something in between and then the layer of particle board. I could get away with PB on both my layers as my studio is on the 1st floor of a house we are converting. Bryan Giles

Yeah, it's never easy figuring out what's the lesser evil when choosing materials - particle board kinda sucks for almost everything, except it's so darn heavy so it's tempting to use it for sound control. Dave, "you have great patience, you should work in tv " - I used to, only in the tech end (design and maintenance) lost patience :? moved north to Oregon, now considering doing post if/when I finally get to build my OWN facility over... On your ceiling, hanging two or three layers UNDER the joists will still only give you a single leaf barrier, since the attic is vented. That can SORTA work if you have heavy cellulose blown in on top of the underside layers, but it's much better if you can manage a double leaf system all the way around your space. We're talking a difference of probably 20 dB or more. Are your ceiling joists actually part of engineered trusses, or what? Can you be more specific about that part of the construction? How deep are the joists, top to bottom? Are there angled "chords" fastened to the joists and to the rafters? Inquiring minds want to know... 8) Steve

Steve, Northern Oregon is beautiful spent some time there on a bike on highway 1 all the way to San Fran. I was braver then. The Joist are 7-1/4" deep on 46" centers. Planning to install more joist to them on 16" centers. Pic should tell the rest. Looks like double leaf at least in the drum room. What is the best way to support the second leaf? The window on the South wall becomes a door and the door on the east wall becomes a window in the bathroom. Thanks, Dave

2 more pics

Man, what an interesting roof design - looks like stick-built trusses on 4 foot centers, purlins across those and rafters on 2 foot centers, every other one being supported by the purlins. Wierd - I'm gonna have to think about this one a bit - can you do a couple more pix on the roof framing from different angles so I can be sure? Also, maybe one shot from up among the rafters looking down the length of the ridge - Thanks... Steve

Steve, Yeah, my father-in-law reffered to it as junk :!: Pic's on the way might have to wait for daylight for some decent light. One concern, the top plate on the wall details all have the ceiling joist (correct terminology?) in common. Shouldn't there be neoprene or something between the top plate and the ceiling joist to keep the individual rooms from sharing a energy? Thanks, Dave

Neoprene wouldn't hurt, but it's not mandatory if you use RC to hang the inner leaf of the ceiling suspended INSIDE the walls, with a 1/4" gap and acoustic sealant. The RC and sealant keeps the ceiling's inner leaf from rigid contact with the walls. If you suspend the entire ceiling, frame and all from above, then you can tie the outer ceiling leaf to the outer wall leaf with neoprene/caulk, and RC the inner leaf the same as before. This method won't work with limited headroom - for that, you'll probably need to just use RC on the joists for the inner layers (leaf) and find a way to put an outer leaf above the joists (cut and fit, cut and fit, caulk...) I'll wait for the pix to get serious. And yes, I was being polite calling it "interesting"... :roll: Steve

Steve, 2 more pics. What if 5/8 rock was screwed into the existing ceiling joist (16" on center) and then 4" down we strung 2x4's off the wall for another joist and hung 2 sheets of 5/8's rock of off RC? With the cellulose blown in on top and insulation in between the 2x4's. Would this be a 2 leaf system? I think I can spare the headroom. Thanks, Dave

Your spacing at ceiling is 48" now, right? If you were to duplicate your existing truss detail complete with chords to the rafters, on 24" centers (one more between each ceiling joist) using 2x8's for joists and 2x6's for chords, you would end up with a short enough effective span to support a steel framed double shell. (2x8, #2 and better, 24" centers, can span 13'6" at 20 live/10 dead load, and almost 12' span at 30/10.) If you then put two layers of 5/8 rock on your (24" centered) joists, then screw 3-1/2" steel 20 gauge studs through the two layers of rock, insulate, screw resilient channel across the steel studs (24" centers) and hang one layer of 5/8 rock on the RC, you'd end up with an STC of about 57 not including any minor gains from more insulation ABOVE all that. This would leave your attic free to breathe. The other advantage of two layers up, one down is getting some "free" bass trapping with the lighter suspended inner panel. Not a lot, but it all helps... That would be much simpler than trying to seal around all those angled chords in the attic for an upper "leaf"; all you'd need to do would be to copy what's there once between each existing ceiling joist... Steve

Steve, That's a plan on the ceiling :D Much better then the alternative. Upon closer review there is no way I can place the neoprene pads directly on the floor. It varys as much as 2-1/2 inches. Any suggestions? I started looking for topics on this with no luck yet. Can you point me in the right direction. I thought I saw someone use bolts into their floor, anyone? Thanks, Dave

Couple of possibilities, one probably expensive and WILL work, one pretty cheap and MIGHT work. First, a couple of things - would you update your profile to include a City you're near? Apparently not everyone read my "sticky" on this, thanks... Second, is your floor smooth but wavy, or is it rough and spalled out? Third (OK, I lied about only two) how is the drainage around your garage and is the slab dry to the touch even in winter? Fourth - If you place a long straight board on edge across the high spots, is it approximately level? are there any spots that would have to be cut DOWN to be level, or just a bunch of LOW spots? I'll give you fair warning, this may not be cheap or easy... Steve

Steve,

I'll give you fair warning, this may not be cheap or easy

Is it ever, heck if it was cheap and easy where would the fun be :!: Smooth and wavy the slab is dry all year around. The biggest issue is the elevation, there is about 3 inches difference from front to back so water will obviously drain out the front of the garage. I have to admit I'm a little concerned about the floor being locked into place. Have folks glued thier neoprene and then glued the floor joist to that? Don't want the floor to float away :roll: Hey Bryan how's the drum booth? Thanks, Dave

Thanks for the profile update - don't need any more shocks about places where sheet rock is $30 a sheet but bricks are almost free... Cheapest easiest way for your floor might be just making variable spacers under floor joists, gluing it all (not sure what glue works for concrete and rubber, maybe liquid nailz) with the rubber against the concrete and glued. 2x4's on 24" centers, even for a balcony with 1-1/2" concrete, can span 4'5" - so, if you went 36" between support points, that should give a pretty solid floor. I would probably clean and seal the existing floor first, then suspend chicken wire at the bottom edge of the joists so the concrete can breathe beneath the insulation. If you use 1-1/8" T&G ply or OSB for flooring, it should work pretty well. Don't forget to plan ahead for any cable trays under floors... Steve

Steve, This is what I came up with any thoughts? On the floor I think we can make it work. I'm thinking of starting the floor joist at the same elevation as the foundation, (which is not reflected in the drawing) it is level. Place neoprene on the floor then cut 2x4's to make up whatever the gap is between the joist and the neoprene in a given place. The gap will vary between 1-3-1/2 inches. Glue the neoprene to the floor glue the filler to the neoprene and then glue and nail the filler to the joist. Make sense? If not I'll draw it up. Thanks, Dave

The floor part made sense, but your comment on the pic about the outer CR wall being single - does that take into account the outer sheathing of the garage? If you add a layer or two of sheet rock between the outside studs before building your inner RC/wallboard, that would give two good mass centers with air space and decoupling. I don't see a problem with that at all... Steve

This detail. Are we saying thae same thing? Thanks, Dave

Yeah - you mentioned adding a couple layers against the Celotex before, right? With or without, you have your two leaves and one space, no problem... Steve

Steve,

If you then put two layers of 5/8 rock on your (24" centered) joists, then screw 3-1/2" steel 20 gauge studs through the two layers of rock, insulate, screw resilient channel across the steel studs (24" centers) and hang one layer of 5/8 rock on the RC, you'd end up with an STC of about 57 not including any minor gains from more insulation ABOVE all that. This would leave your attic free to breathe.

With the ceiling on RC will there be enough isolation to nail the top plate to the joist? Since my walls are sitting on top of the floor more than one person has expressed concern of the floor shifting and the walls being secure for that matter, hence the previous question. I've decided on a 1" gap between walls due to space, if I glued two pieces of 1/2" neoprene together for spacers between the floors to keep them from shifting, is the neoprene sufficient for isolation between rooms. On the garage outside walls(these are the walls that form the 90 degree angle in the control room) 2 layers of 5/8's on RC or 5/8-1/2-5/8? By the way if anyone is looking for materials in Colorado I've located everthing except for Mineral Wool and I haven't really looked for that yet. Thanks, Dave

"With the ceiling on RC will there be enough isolation to nail the top plate to the joist?" - you could as long as ALL your inner wallboard (walls and ceilings) is on RC - if you want a few dB more isolation, you could use resilient sway braces instead - one I drew up is here http://www.johnlsayers.com/phpBB2/viewt ... c&start=75 and another here - http://www.johnlsayers.com/phpBB2/viewt ... &start=165 And a pic of Aaron's implementation, near the bottom of this page - http://www.johnlsayers.com/phpBB2/viewt ... &start=210 "if I glued two pieces of 1/2" neoprene together for spacers between the floors to keep them from shifting, is the neoprene sufficient for isolation between rooms." - sure, but I wouldn't do continuous neoprene, just some 2-3" pads every few feet. "2 layers of 5/8's on RC or 5/8-1/2-5/8? " - unless your noise situation has deteriorated since we last discussed it, two layers of 5/8 should do fine. "if anyone is looking for materials in Colorado I've located everthing except for Mineral Wool" - These guys supposedly sell rigid fiberglass - http://www.spi-co.com/servicecenterdire ... v?detail=3 One reminder - before you commit to anything you're not absolutely positive on, ask yourself if you're violating the mass-air-mass principle in any way, including proper decoupling from inner leaf to outer leaf - if you're not sure, fire some more questions/pix til you're sure. I'd much rather be able to say "no, you shouldn't do that" instead of "oh, shit, you did what??!?" Got any pix of what your roof framing looks like with the changes? Need any more ideas on ceiling construction, or is that all set? (Nosy bastard, ain't he? :roll: Steve

I'll take some pics. I don't have the resources to make the brackets an idea was a large neoprene grommet. Drill a hole in the top plate (steel) the outside diameter of the grommet is 1" the hole is 1/4" and the thickness of the grommet wall is 1/4". Slip the grommet in the hole of the top plate and use a wood screw through the hole and into the rafter. The screw is touching the rafter and the neoprene grommet and the plate is seperated from the rafter by the grommet. Attach every2, 3 or 4 feet. Good, bad? If good can I do away with RC on one leaf?

you could as long as ALL your inner wallboard (walls and ceilings) is on RC

- I think I know the answer to this question but here goes. Even with 25 gauge steel? Again a big thanks for your help and yes I'm trying to avoid the oh shit :shock: Dave

The grommet thing might work, as long as you have "sag room" - snow loading might cause a slight isolation loss from deflection of ceiling joists. You only ever need RC on one side of a wall, even with wood studs - if the entire wall is 25 gauge steel framed, no RC is needed period. Plus, you wouldn't be using nails for steel framing, (hopefully) and 25 gauge studs are NOT for load-bearing walls... Steve

good thought on the sag since my roof had over 4 feet of snow on it 2 years ago! Ok, so if the top plate was attached(no nails) directly to the rafter or with grommets. Will the 25 gauge walls sitting on a floated floor with a ceiling on RC give enough isolation. Dave

Still need to know what your roof framing is like now, and whether you meant "joists" when you said "rafters"... Steve

Rafters that are in place and the ones that were added. Dave

OK, so you followed my suggestion and built trusses in place between the 4 foot centered ones in previous pix, so now you have full trusses on 24" centers, right? From the pix, you already had rafters on 24" centers, but every other one just had a collar tie - BTW, rafters are the sloped boards and the joists are (in the case of trusses) also called bottom chords - I'm still confused as to wanting to connedt the wall frame to "rafters", instead of the horizontal "joists" - In any case, trusses are designed for specific loads in specific places - even if your 25 gauge studs were strong enough to use as load bearing, it would be a very bad idea to try and support any point along your trusses from below - the truss was engineered ( I hope) for specific loads pressing down on the top (roofing, and snow) and the bottom chords, while they can have a certain amount of weight hung from them, should NOT be supported from below - doing this distorts the geometry of the truss when loads (snow) are added to the top, causing the truss to fail. This is why I don't recommend having walls added under a truss roof unless you leave enough of a gap between top caps and ceiling framing to allow for the amount of sag that's designed into the system - for rafters and ceiling joists, this is typically L/240, which means that the span in inches divided by 240 = the maximum deflection at the center of the span that is allowed. This is what span tables are based on. What this means, is that if your roof is (was) engineered trusses, they should have been set up so that with the maximum load the roof is designed for, your midpoint shouldn't sag more than span/240 - so if your span is 20 feet (240 inches) then span/240 would equal 1 inch of allowable sag. I'm not enough of an engineer yet to understand all the reasons, but from what I've been told supporting a truss from below while stressing it from above can get pretty ugly - for that reason, I don't recommend solid walls touching trussed ceilings with anything other than flexible materials - maybe something like a closed cell foam along both sides of the top cap, bolstered up with acoustic caulk on both sides - One of our members, Rod Gervais, knows a lot more about this than I do - maybe we can get him to add his thoughts to this before you make further decisions... Steve