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upinsmoke 04-23-2010 04:47 AM

Spray foam or rigid for basement walls?
I looked at bunch of the forums searching for the answer to the above question and couldn't find a definitive one - maybe there isn't one.

The house is in Western North Carolina, poured concrete walls, 3/4 under ground and has two coats of Dri-Lok. I'm getting ready to stud it out and just want to plan ahead for the wall insulation.

So, is there a consensus, or can I hear the differing opinions?

Thanks as always for the great information.

Just Bill 04-23-2010 06:10 AM

I like the 2" foamboard with the notches in for furring strips. The strips are screwed (tapcons) to hold the foam, and can also hold the drywall, no need for framing.

Chemist1961 04-23-2010 06:35 AM

I am stuck on this too, there is rigid low density which offers breathability and rigid HD which creates a non breathable barrier and rigid reflective foil faced.

jogr 04-23-2010 11:14 AM

The most important thing is to make absolutely sure all water/moisture issues are completely resolved before closing it up. Spray foam works great in the rim joist area. Foam board can be used but a little more tedious to fit into the rim joist. On the wall surface foam board is easy to use and usually cheaper than spray foam.

upinsmoke 04-24-2010 05:07 AM

Thanks. I'm very fortunate in that the basement was totally dry from the start (fingers crossed that it stays that way) and I added the two coats of dri-lok, so I hope I'm good in the moisture department.:thumbup:

So it sounds like foam board for the walls with all seams taped with tyvek or similar. Then, I agree, spray foam is best (or at least less time consuming) around rim joist area - so the question is will a company come in and spray just the rim joist, or do I buy a truck load of spray can foams?

Also, if I do it - is there more than one type of foam? Seems like I read here somewhere about an insulating "fire barrier" type of foam? Any help/experiences in this area would help out.

Chemist1961 04-24-2010 06:30 AM

Foam gives off toxic smoke, must be sealed in most areas with a fire barrier min of 1/2 " drywall. You cannot buy any canned foam that I have found for the rim joist which covers a flat area, only as a gap filler or corner bead. There is low and high expansion, ie low is to prevent bulging around windows and doors. If you find a surface coating foam in cans please let me know.Gap filling foam will just drip off a vertical surface if applied thick. You can cut and tuck rigid and seal the edges but I used ROXUL rock wool which is fire resstant and has no itch. Then used rigid foam only for the really tight areas where the wool would not tuck without crushing.
However I did my entire 160 ft rim joist with LOW Expansion foam and a gun with a dial adjustment. I did up and down the inside corners of each joist bay, along the top and bottom edge of the sill plate and the top edge where the floor above sits on and meets the joist. Then I ran out along the floor at each joiust 8-10 inches from the wall. I then stuffed each bay with fresh R23 and tucked back the old R10 on top rather than waste it. I also pulled old tucked fibreglass from around each window and resealed there with foam. I paid special attention to the dryer vent and other perforations. Net cost about $160 and 3 hours labor. Foam trucks want a minimum to show up , at least $500.
Next step, I have sealed under 75 % of my baseboards as well, using latex for easy cleanup in this area.
Net result over 45 % reduction in air loss. 35 yaer old house is far less drafty. One heating contractor told me over 15% of household heat can be lost through a leaky rim joist:eek:
I actually got an Extra $$$ BONUS rebate for exceeding audit expectations by over 20% my air sealing measured so well. Air change rate in the house will affect your ventilation system. I started with equivalent to a 268 square inch opening. House is far tighter now. Once I do the basement walls and if I complete the baseboards I may need to add an HRV as my air change has dropped from 6.4 to 3.5 .

upinsmoke 05-02-2010 04:23 AM

I'm still exploring/researching the pros and cons of spray vs rigid foam installation. Has anyone heard of any code issues or problems with either high or low voltage wiring being an issue with the spray foam. Either heat build up or any interference?

For you electrical guys - can house or low voltage wiring be run in conduit from the ceiling down the wall to the switches or receptacles? I know it may be above what the code calls for, but it would also eliminate the heat issue - if there is one.

House is in Cherokee County, NC.

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