Polyurethane / Condensation

Aiken Colon

You might want to go over to sprayfoam.com and check around on there. Not sure if there is a message board or not, we just became a sponsor there. I just know it is completly dedicated to sprayfoam and those guys might have your solution as well.

JJ

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When they spray such a thin layer of foam on the roof deck then don't fill the cavity competently with insulation it can cause convection problems in the air space between the insulations (I have seen one inch of foam covered with an r-11 batt in a 2x12). Fiberglass does not do well with air movement. Additionally many foams have to be applied when the wood has a certain water content or it can cause problems like it separating from the roof deck. Many times the foam is applied early in the construction when the building is more or less open to the elements resulting in mosture problems.

10fingers

There should be airflow allowed under the roof to keep it cool in the summer so the shingles don't bake. And in the winter to keep it cool so you don't get ice dams.

Yup what Leo said. Same problem I have on my 4/12 pitch. I have 4500 sq. ft. of roof area. All of it is vaulted with 1.5" of ridgid insulation and that's it! You want to talk about roof dams, mine run the length of my house and are as high up as 3 feet from the ridge. A roof deck in my opinion, and this is a contested topic by many engineers, should always be vented underneath. A cold roof is vented under the deck. A hot roof would be one where the void, lets say in a vaulted roof, is entirely filled with insulation like polyspray. I don't like the hot roof because the heat of the house will hit the deck and assist with snow melt. Has to the heat has no where else to go. But if I vent in the void then that heat leaves before heating up the deck. Now the only heat I get hitting the deck is the radiant heat from the sun.

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MEL

[quote=Quinn;589098]Drywall will make it worse. It will fill with mold.

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AaronB.

the dewpoint is located on the surfa ce of the foam instead of within it. If the foam were 3 inches thick, then this would place the dewpoint within the foam assembly and eliminate this problem.

Add a couple more inches of closed cell foam and get rid of the fiberglass.

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BarryZ

Quinn,
Have you had drywall installed already? Did you go back in to see if just adding drywall fixed moisture migration? IMHOP, the most practical solution (without having to rip out or re-spray), would be to add a good vapor barrier between drywall and paperface fiberglass. Just stop the moisture from entering cavity.
If drywall is installed, have your painter apply the best vapor barrier primer available before finish coat.