Open cell spray foam

S

Scruffer

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I have a 30' x 60' shop, gable. All wood construction. 9' ceiling with open attic. Roof trusses are on 2' center. 6/12 pitch. The walls are insulated with fiberglass batts and OSB wall covering. I am not planning on putting any kind of sheetrock or wall board on the ceiling. The roof sheathing is OSB, asphalt shingle for roof covering. I can go with fiberglass batts or foam panels or open cell spray foam. The spray foam seems to be the best insulator? Your thoughts appreciated. Thanks
 
Scruffer said:
I have a 30' x 60' shop, gable. All wood construction. 9' ceiling with open attic. Roof trusses are on 2' center. 6/12 pitch. The walls are insulated with fiberglass batts and OSB wall covering. I am not planning on putting any kind of sheetrock or wall board on the ceiling. The roof sheathing is OSB, asphalt shingle for roof covering. I can go with fiberglass batts or foam panels or open cell spray foam. The spray foam seems to be the best insulator? Your thoughts appreciated. Thanks
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I live in Oklahoma where the weather can get down to the single digits, but usually not for long. I haven't installed any heaters yet so that's another rabbit hole for me. I am on propane. And right now, I am paying $1.95 per gallon.
 
ddickey said:
Why open cell?
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It's suggested if you're using spray foam for insulation, that you use open cell on the roof ceiling. It breathes better so it keeps condensation from forming between the sheathing and insulation. Gable roof with good ventilation.
 
Interesting. Closed cell has an R value of 7 per inch. Open cell has an R value of 3.8 per inch. Don't know. I just do not want any problems down the road. My roof is only 4 years old. Good quality shingles. It qualified for an insurance discount because of the hail rating value.
 
In a cold climate, moisture will travel from the warmer inside of a structure to the colder side. As the moisture travels through open cell insulation, it will reach a point where the temperature is below the dew point and the moisture will condense and potentially freeze. This reduces the effectiveness of the insulation and potentially leads to mold, mildew, and rot on the cold side of the barrier. With closed cell insulation, the vapor barrier starts at the warm side.
 
I put open cell spray foam in my walls and I’m very pleased. Through consecutive 100 degree days this past summer here in central Texas my worst bill was $65 to cool 2100 feet. It’s my understanding that

Open cell is half the cost of closed cell

The difference between the two is negligible on your power bill

Closed cell will make your structure significantly stronger
 
A lot of spray foam contractors around here spray 2" of closed cell then top off the cavity with open cell. I have done a few buildings like this and it seems to work very well.
 
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