Cost of spray foam under roof deck
The architect used attic roof trusses on a long single floor home that create a large square attic walking space in the middle like a long bowling alley since the house is 84 feet long. Width is 26 feet wide of the roof trusses. A perfect rectangle. Walls are 12 feet tall.
The rafters under the roof deck are 10 inches deep and the rafters making the roof trusses floor, or 1st floor ceiling is also 10 inches. The center bowling alley shape is framed so I could insulate this long square walk up attic on the two sides and across the ceiling of this center area.
When doing the math, the interior roof underdeck is 83 1/2 feet long and has 42 to 44 trusses that are 1.5 inches wide each, so about 5 feet wide of truss space to minus from the 83 1/2 feet. I figure 5 feet x 18 x 2 x $7 a sf comes out to around +$1400 so not sure if these installers back this out. Anyways, I’m told $1 to $1.15 is the cost or 7 times this number since the roof needs 7 inches of thickness to get R49. When I do the divide the math on a 2 inch closed cell foam board from Lowes or Home Depot, it comes out to about 59 cents per inch foot as the installers are technically installing $2.30 for the same 2 inch SF. Do these foam costs seem right to some of you installing close cell spray foam? Basically these quys want $21,000 to $22,000 to spray under the roof deck so I was wondering if I am better off with another solution but not sure what to do, as I thought this was solved until I got the quotes. Isn’t there an option where they attach mesh or fabric of some sort and blow in a type of insulation as an option under the roof deck? I am thinking maybe just get R49 Fiberglass installed in the 1st floor ceiling and insulate the sides and ceiling of the attic bowling alley area, but that would not allow future access to the sides of the bowling alley which may have duct work installed in it. Thank-you everyone in advance for any ideas.
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