closed cell foam to prevent condensation on metal roof
luce myers
| Posted in Energy, Heating & Insulation on
We are working on new construction and it is not quite closed in when the freezing rains came. We notice condensation dripping within from the metal roof. Should we consider one inch of closed cell foam to prevent more moisture from collecting or will this correct itself when we close in the building and add another type of insulation later before sheet rock? Help! Luce and Rich
Replies
You one way or another need to lower the level of humidity (dewpoint) near the roof. Insulation alone doesn't do anything (unless bonded to the metal) since the metal will always be very close to the outside temp, and it's the dewpoint at the metal that determines whether condensation will occur or not.
What are the
existing and proposed materials, from the metal roof on down? Is the roof installed over plywood? Felt? Purlins? Or what? Were you planning on insulating and installing drywall?
To prevent moisture on the metal ... spraying foam on the metal will work since condensation occurs where laden air meets metal and if you eliminate the air, you eliminate the condensation.
However, you're being a bit premature in that it sounds like you're still under construction. Metal roofing can pose prolems if you need to vent e.g. an attic. If your end result is a well vented attic/ceiling, you should have no problems. Your ceiling should be well sealed and your exhaust/vent system designed and working well to ensure good control of moisture generated in the house.
If you mean to add e.g. 1 inch of rigid to e.g. a delta rib roofing (which leaves air spaces), you cannot be assured of eliminating moisture unless you can guarantee no air circulation behind the insulation (which I'm suspecting won't happen).