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-   -   Rigid foam behind DWV (http://www.diychatroom.com/f19/rigid-foam-behind-dwv-77171/)

benjamincall 07-26-2010 06:00 PM

Rigid foam behind DWV
 
I have PVC drains along two block walls in the basement. I plan on framing out the wall about 3.5" from the block to accommodate up to 3" PVC. My plan was to adhere the 2" rigid foam insulation to the block and use fiberglass batts inside the 2x4 wall.

Since my drains have very little clearance from the wall, should I cut channels in the 2" foam insulation? If cutting out channels for the drain is the way to go, should I fill the gap with expanding foam?

Gary in WA 07-30-2010 12:03 AM

Non-expanding. Don't forget to fire-block the wall every 10' horizontally and at the top, per minimum safety/building code. Remember the sill sealer under the bottom p.t. plate for a capillary and thermal break. No air space between insulation types for a convective loop. Latex paint on drywall with no vapor barrier. Foam board at the rim joist.

pp.#4: http://www.codecheck.com/cc/images/CC5thEdSample.pdf

http://www.lowes.com/lowes/lkn?actio...248&lpage=none
http://www.greenbuildingadvisor.com/...-building-code

http://oikos.com/library/insulating_...lls/index.html

http://www.rd.com/57548/article57548.html

http://www.buildingscience.com/docum...gs?full_view=1

I could go on like that battery rabbit, I’ll stop now…..

Be safe, Gary

benjamincall 07-30-2010 09:43 AM

Gary,

I thought all spray foam, even the window and door stuff, expanded somewhat. To what kind of foam do you refer?

For the PT bottom plate, I was going to borrow an idea from Todd at homeconstructionimprovement.com. He uses a piece of composite decking under the bottom plate. What do you think?

I'm thinking I'll just do away with the fiberglass batts and use 3.5" of foam right up to the framing, leaving the stud cavities empty. In that fashion, I should be able to avoid a convective loop because the foam and the drywall will be basically the same temperature, eliminating the convective loop.

As far as fireblocking is concerned, if I have any gaps, I'll seal them with fire foam.

Thanks for the reading material!

Gary in WA 07-30-2010 03:20 PM

"I thought all spray foam, even the window and door stuff, expanded somewhat. To what kind of foam do you refer?" ----- Whoops, meant window and door..... don’t push the piping out of whack from proper drainage.

"For the PT bottom plate, I was going to borrow an idea from Todd at homeconstructionimprovement.com. He uses a piece of composite decking under the bottom plate. What do you think?" ---- I wouldn't do it because any water and there will be mold.


“When composite materials first came out, mold was a major problem caused by the use of certain recycled materials in the "wood" that fostered mold and mildew growth. The industry has come a long way since then, working hard to eliminate mold problems in the material altogether. You may, however, still experience some deck mold, especially in wetter climates.” From: http://www.servicemagic.com/article....eck.11064.html
So any water on composite could cause mold especially with a nice warm room just on the other side of the ” drywall, because of the ingredients of composite.
“Composite decking isn't bulletproof, however. The wood component can make these boards susceptible to mold, mildew, and under the right conditions, decay.” From: http://www.deckmagazine.com/article/80.html

Also from that article: “Lower proportions of wood flour mean most of the particles will be encapsulated by plastic and safe from water. When the percentage of wood flour reaches 50 percent to 60 percent, some particles inevitably will touch each other, making water absorption more likely.

Some manufacturers might not disclose the ratio of wood flour to plastic in their decking; in those cases, the best bet may be Stark's eyeball test. A large number of prominent wood particles on the surface doesn't mean the decking should be avoided, but it is an indication that the planks will be more likely to absorb water. “
So it matters how much wood flour is used and the pressure used to produce it.

Yet sill sealer is made specifically for that:
“Air and moisture barrier
Stops heat loss and air infiltration at the foundation to sill plate
interface
Eliminate costly callbacks to builders due to leaks
Mildew and water-resistant
Provides protection against sill plate rot” from: http://docs.google.com/viewer?a=v&q=...Sf-fmaa9ayOUVg

Be safe, Gary

benjamincall 08-14-2010 02:27 AM

http://www.youtube.com/watch?v=VHF74HQPZtM

You'll have to forgive him for saying that 1/4" is smaller than 3/16".

I'll using 2x4s to frame out my basement walls, so I guess I'll just tack the extra two inches of sill sealer to the back of the studs.

Edit: Now that I've thought about what I saw in that video, I'm not sure stapling the sealer to the bottom plate is such a great idea. A staple will compromise the "capillary break." The sill sealer is made of polyethylene, so I will probably use something like this contact cement:
http://www.amazon.com/3M-90-24-Spray...1771741&sr=1-1


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