Basement – Cost of XPS panels vs. sprayed closed cell foam

basementinsulation

I'm starting the process of finishing my nearly full height (7'2") basement and am costing out the insulation. Based on my research of what's best below grade, I'm debating between XPS foam panels (DIY) vs. sprayed closed cell (definitely not DIY).

Based on the cost of the panels at HD ($31) vs. professionally sprayed foam ($1/board ft. quoted) it looks like the cost differential for my square footage (~140 lineal ft.) at 2" depth is about $600. There is a $400 utility company rebate that I would qualify for if I got it sprayed. This is close enough for me (~$200 after rebate) that I'm thinking that I shouldn't bother with DIY and just have it sprayed by a pro.

Is there something that I'm missing in my math below?

137.6 lineal ft.
7.2   height ft.

986.0   sq. ft.
2       in. depth
1972.0  board ft.
$1.00   closed cell spray foam per board ft.
$1,972  closed cell spray cost (contractor -$400 utility rebate)

38      XPS (4x8) sheets
$31.22  Home Depot per sheet price
$1,186  XPS sheets cost
4       Foamular JointSealR tape rolls (90 ft. per roll)
$36.00  Foamular JointSealR tape cost/roll
$144.00 XPS tape cost
12      GreatStuff cans
$4.00   GreatStuff can cost
$1,378  XPS insulation cost (DIY)

Best Answer

There's a sizable difference in how "tight" (well-sealed) you'll get a DIY installation, even with the tape and GreatStuff in your calculations, vs a proper closed-cell foam spray job. In most homes air movement is as big of, if not greater, culprit for heat loss than passive heat loss. So if the cost of DIY is even close to a pro job, then the pro job will pay for itself in spades.

However, 2" of foam is below what's required for code here in Illinois, if that's all the insulation the wall would have. So check on that. It's important you get the right amount of foam... if not then you can build up condensation on the inside of the foam and end up with mold. There's a lot of misinformation out there about this, so the simplest solution is to just make sure you follow code.

Also, make an effort to check up on the contractor. According to the experienced guys who did my house, if the two components of the foam aren't mixed just right, the foam can either not work correctly or spontaneously combust while curing. I'm sure the latter is rare, but the former would be undetectable to the naked, untrained eye, I would imagine.

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