Attic Insulation II

JoeMilner · Post by **JoeMilner** » Mon Jan 12, 2004 11:30 am

Hi Steve
The wainscoting/ panel absorbers turned out great, thanks again!
I'd like to improve the TL of the ceiling, which if you remember is
5/8" d-wall on the ceiling joists, no insulation above, and about 6 feet of attic space between it and the also-non-insulated roof.
What do you think of 1 or 2 layers of mineral wool in the joist cavities, and maybe a layer of the Acoustilead/ Sheetblok-type barrier? Then, would a layer of plywood on top of that help? Hinder?
Not that I'm lazy, but physically getting 40 sheets of 3/4" plywood up into the attic, and then maneuvering it 80 feet to the back of the theater where the ADR stage is sounds like a BIG pain in the ass. And, a lot of time which I don't really have to spare. I'm sure anything beyond the "nothing" which is there now would be an improvement.....but how much an improvement?
Any thoughts?
Oh, and Happy New Year everyone!!

PS
Again having trouble w/ PayPal, it seems to freeze when loading the "Confirm Payment" page......

knightfly · Post by **knightfly** » Wed Jan 14, 2004 8:39 am

Hey Joe, glad things are working for you so far - as to this question, I just checked back on your first post and you were interested in making the attic function as a bass trap - it can't be both a bass trap AND isolation, you need to choose one or the other - If you were to use it as a bass trap, then you'd need a "backup" - the roofing beyond the trap would need to be a double leaf barrier with air/insulation between the leaves.

Have the panel traps worked well enough that you now don't feel the need for more bass trapping, are you like me and having occasional "brain farts", or is there a third possiblity?

BTW, sorry for the delay - the abnormal ice storm we had here has my entire place (almost 10 acres) looking like somebody LARGE was playing "pickup sticks" and forgot the "pickup" part... Steve

JoeMilner · Post by **JoeMilner** » Wed Jan 14, 2004 9:06 am

Hi Steve
Yeah, the attic is just an attic, not a giant basstrap. I'm hoping that the panel absorbers and the 2" Select Sound 703 panels hung from the ceiling (at 6 deg angle, 2" to 8" from ceiling) will be enough for the low end. So, it's now back to increasing the TL through the ceiling from the non-insulated attic/roof.

Thanks!

knightfly · Post by **knightfly** » Wed Jan 14, 2004 9:47 am

OK, tell me more about those "bow trusses" - describe them completely - spacing, size of chords, wood or steel, etc - I'm thinking that if you have the support you'd be better off building IN and down, instead of UP and OUT... Steve

JoeMilner · Post by **JoeMilner** » Wed Jan 14, 2004 10:02 am

The bowstring trusses are wood, about 16 feet apart, and 45 feet long as they span the whole building. There's one that runs right over the stage and control room, not quite centered, more about 1/3 of the way from the south side (the stage runs east/ west). There's a truss just outside of each north/south perimeter wall at the control room end , so they begin to cross into the stage area as the walls are splayed 4 degrees and thus the stage becomes wider moving towards the screen.
My main concern is doing ANY construction inside the stage area now that the screen is installed, as once one of these type screens is up, you don't want any dust/debris/risk of contact anywhere near them.
The stage has been forced into service way before it was completely done (obviously), which is nice because it means I'm busy, but not so great in that I've had to proceed with the construction process in a not-always-logical manner.
So, what can I do in the attic?

knightfly · Post by **knightfly** » Wed Jan 14, 2004 10:19 am

We'll eventually get to that answer, but I still need to know what's holding things up right now - if your bow trusses are 16 feet apart, what's holding up the sheet rock - you mentioned joists, what are their dimensions/centers/spans? Basically, I need to "see" what you see when you're up in the attic.

I'm not trying to be difficult (guess it just comes natually

) but I don't want to suggest something that's going to get anyone hurt, especially in quake country... Steve

JoeMilner · Post by **JoeMilner** » Wed Jan 14, 2004 10:31 am

Oops, sorry.
The joists are at roughly 16" OC, and for the most part are 2x6. And, being 1930 construction, they actually are 2" x 6", not 1 1/2x 5 1/2". Rough lumber. The trusses are about 6 feet high at the center, curving down to nothing at the sides.
Let me know if you need more info.....

Thanks!

knightfly · Post by **knightfly** » Wed Jan 14, 2004 10:48 am

Getting there - now, for the longest span of the joists, and any bracing out of the horizontal plane (tied to trusses, or just spanning two end supports (which are how far apart?), etc, IOW is there ANYTHING fastened to them topside that would interfere with sheathing... Steve

JoeMilner · Post by **JoeMilner** » Wed Jan 14, 2004 10:57 am

Probably the longest un-supported span is about 12 feet, as the north-south walls support the joists at points between the trusses. There's some rigid conduit in a couple places on top of the joists, which could be re-routed. Mainly, sheathing would just be a huge pain to physically maneuver the 4x8 sheets up the stairway, up the ladder into the attic, then shoe-horn it back the 80 feet or so to the stage area (the access is in front, the stage is in back) while tightroping along the joists and to MAYBE get it through the webbing of the trusses themselves. I'm not even....well, it MIGHT be possible, but that's still around 25 sheets.
So if there's any way to get comprable performance with a material that's a bit more maneuverable, I'd love to hear it. I s'pose I could cut the sheets into 4x4s, maybe that's the solution.

Thanks for all your attention on this one, sorry to hog the forum!

knightfly · Post by **knightfly** » Wed Jan 14, 2004 11:12 am

No prob, it's not picked up to full speed since our 2-week outage due to Aussie tel's booboo -

I don't have span tables that show REAL 2x6's, but they should be real close to today's 2x8's if not stronger - I'll check out spans in a sec and see what's doable.

You've heard the expression, "good, fast, cheap - pick any TWO"?

You might be able to put insulation batts between joists, then a couple layers of something like Auralex' Sheet Blok - the cost is horrific, the stuff is heavy by the roll, but might be easier than ply, and about the same isolation. You'd need to be able to tape between rows, to maintain hermetic seal. I'm not sure the stuff has ever been used quite in that way before...

4x4 sheets would definitely be easier to handle, with twice the caulking needed.

If you could drape your screen with plastic and seal around it with duct tape, could that work? It would be so much easier to put up 6" steel joists under your existing drywall, then hang resilient channel under that and put up two layers of drywall with R38 batts between... Steve

JoeMilner · Post by **JoeMilner** » Wed Jan 14, 2004 11:48 am

Yeah, it'd probably be easier, but the problem is that I now have to finish this part more or less "in-flight" as I'm working in the space continuously for the next few months. So, working in the attic would be invisible, so to speak. Thanks for the info, though!
If the Sheetblok stuff is only "comprable" to plywood, and not markedly better, then I'll probably do 4x4 sheets of plywood (and twice the caulk).
Last question; 6" batts or layer(s) of mineral wool?
Thanks again!

knightfly · Post by **knightfly** » Wed Jan 14, 2004 12:00 pm

For this application, the Sheet Blok would probably come out about the same, for 5 times the cost. It would also be harder to seal, without a rigid backing of some sort.

You'll get best damping of the lower panels by putting R38 batts in - best combo of materials would likely be to use R19 batts under 2" mineral wool, in 2.5 to 3 PCF boards. The batts will damp the lower panels (improving TL) without excessive hard contact, and backing them up with a couple inches of rockwool will improve overall TL of the assembly.

With that old, hard wood you may need to drill pilot holes and screw everything in place to avoid splitting wood/bent nails -

Of course, acoustic caulk sealing everything... Steve

JoeMilner · Post by **JoeMilner** » Wed Jan 14, 2004 12:11 pm

Thanks a zillion, Steve!

knightfly · Post by **knightfly** » Wed Jan 14, 2004 12:17 pm

No prob - forgot to mention span calcs for 2x8 Doug Fir #2 on 16" centers - tables show max of 16'6", so your 12' span should be fine with your REAL 2x6's as discussed... Steve