Insulation: types and how to mount?

[Finally]

The plans for walls and ceilings discuss insulation but is not clear what type and how to use. In fact various sites give conflicting information.

For a wall, either staggered wall or RC channel on one side, what's the best insulation (batting or OC 703(how thick)) and what is the most effective way to mount it?

For a ceiling with 2X8 joists and RC channel....same question.

Speaking of RC channel, is it really safe to use RC-1 channel on the ceiling with 2 layers of drywall?

Thanks folks!!!!

[knightfly]

Inside walls, insulation density isn't quite as critical as it can be for absorbers; generally, since it's sometimes hard to find a specific manufacturer's stuff locally, as long as you stick with 2.5 PCF up to maybe 6 PCF density, any porous insulation will work about equally. Stuff by Rockwool, mineral wool, slag wool, rigid fiberglass (like OC 703), Roxul SAFB's (Sound Attenuating Fire Blankets), all will work well in walls.

The main thing is to make sure the insulation is in light to medium contact with the inside wall surfaces; best way to do this is to slightly overfill the entire cavity. Second best, for walls, is to put batts up against both inside wall surfaces, and hold them in place with light lath fastened to the inside frame edge (assuming double frames, that is) - this way if you can't afford the extra insulation for a complete fill. It's also good to put the heavier stuff against each inner wall surface, then fill the rest with UNFACED standard house insulation fiberglass batts.

When doing double framed walls and a fire stop is demanded by code, the IBC recognizes mineral wool/fiberglass wool as a firestop material; this will keep inner and outer frames from hard contact with each other and still meet code. Check your LOCAL codes to make sure this hasn't been contested by your friendly local bureaucracy...

Ceiling insulation - again, all the above; only real diff is if you can't afford a complete fill, gravity will save you having to "rube goldberg" a way to keep the batts in light/medium contact with the ceiling layers - it's still better to completely fill, just not TOO full so upper and lower panels are "shorted out" acoustically.

Where applicable, impaling clips work for the heavier fire blanket types and 703, rockwool, etc - if you can't find these locally (industrial insulation contractors usually) they can be had on the net

http://www.acousticalsolutions.com/prod ... _clips.asp

Speaking of RC channel, is it really safe to use RC-1 channel on the ceiling with 2 layers of drywall?

Sure, no prob as long as the joists will take the weight; for 24" centers on joists, RC should be 16" centers (plus one extra where each seam of the first layer goes, so each sheet has its own RC to screw into) - for 16" centers on joists, RC should be at 24" centers - when in doubt, you can divvy up the space by one more, putting the RC at 12" or 16" centers (wider joists, narrower RC spacing) - this combo would hold 3 layers of 5/8 wallboard.

All this presupposes that you're NOT using nails, you use the correct type and length of screws, and you mark all screw locations on masking tape strips along the edge of the surface BEFORE you start, so you won't have one layer's screws collide with another and weaken the fastening...

Hope that helps... Steve

[Sword9]

Please forgive the noob question here, but what's lath?

[knightfly]

Sorry: replace that with "skinny little boards" - not sure where the original term came from, but if you tear down a really old house you will likely find the walls done with "lath and plaster" - these little slats (about 3/8" x 1-1/2") are nailed to the studs, spaced about 1/2" apart, then plaster is spread over them; the gaps allow the plaster to ooze between the slats (lath, which is both singular and plural) and this ties the plaster to the lath to form what has since been replaced with sheet rock -

From American Heritage Dictionary -

lath (l²th) n., pl. laths (l²thz, l²ths). 1.a. A thin strip of wood or metal, usually nailed in rows to framing supports as a substructure for plaster, shingles, slates, or tiles. b. A building material, such as a sheet of metal mesh, used for similar purposes. 2.a. A quantity of laths; lathing. b. Work made with or from lath. --lath tr.v. lathed, lath·ing, laths. To build, cover, or line with laths. [Middle English latthe, probably alteration (influenced by Welsh llath, rod) of Old English lætt.]

You can still buy lath (sorta) at building supplies, typically in bundles about 3 feet long, with one end sharpened; they're used for layout on foundations, gardening stakes, etc... Steve

[Sword9]

Thanks for the clarification!

All my google-ing for lath came up with this wire mesh stuff.

[mcguin]

hi all
I am building our second studio. This time around I can only find paper faced fiberglass bats locally - any problems using the faced bats?? - I plan on filling the cavity between my double walls with this (3 layers of drywall/rc on each outer wall.

thanks in advance

dan

[sharward]

any problems using the faced bats??

Hi Dan... I spent a good 5-10 minutes searching for the thread on here, but I couldn't find it. Thus, you'll have to settle for a paraphrase. I recall knightfly mentioning the fact that the paper acts as a third leaf of sorts, so it is not a good idea to use faced batts. However, in a pinch, you might be able to remove the kraft paper.

[z60611]

the paper may also be a vapor barrier, and having more than one of those in the wall may be bad.

[subatom]

You can still buy wood lath at building supply stores (not stakes). It is just called 'lattice strip' now. Wood lath is rarely used on new construction, as the metal lath requires less time to put up, and has better "grab".

**before the terms "lath and plaster", it was refered to as "waddle and daub" which was really just sticks and mud.