Expanding foam insulation under metal roof?

Guest User
8/4/2007
Help! I am building a house in southwest Virginia and contractor installed metal grand rib roof over purlins with no vapor barrier. The roof is a shed style truss roof with a 3/12 pitch. There should be good ventilation since there is about 12” to 36” air space between the purlins and the insulation (R30 batten) with soffit ventilation on both ends. The building code in virginia is to follow the manufacturer’s guidelines. The building inspector has advised me that I will “probably” have a condensation problem in the winter when temperatures get below 40’s. My contractor tried to cut corners and did not buy directly from manufacturer but a local sheet metal fabricator. When I checked with the fabricator regarding installation guidelines… he says he uses 4 different manufacturers and does not know which manufacturer is mine and that there is no guidelines??? The contractor is suggesting that maybe adding expanding foam insulation would provide a vapor barrier. I don’t know what to do.
Todd Miller
Classic Products, Inc.
8/4/2007
For good info on venting, visit www.airvent.com. Ideally you want lots of eave soffit vents as intake and a ridge vent as exhaust. Based upon what I know, you will probably have condensation issues. Spraying the back of the roofing with icynene foam would help avoid condensation and also help with sound transfer. Has your supplier been able to give you a written warranty on the panels?
Guest User
8/4/2007
Thanks Todd, will check out www.airvent.com. I do not have ridge to vent ... since the roof is shed style and flat but on a 3/12 pitch. There are soffit vents on all four sides (42x36) with 2' to 3 1/2' overhangs. Oddly enough the supplier gave a 30 year written warranty on the panels. He has been in fabricating business for about 15 years so ... who knows if he will be around when/if needed. I am not sure it would be physically possible for anyone to get up into the trusses to spray the foam onto the back of roofing. I think what the contractor had in mind was to pump the foam in through lines which means it would end up on top of the batten insulation... not on the back of the roofing. If the foam were not on the back of panels but on top of the insulation ... would that still help?
Todd Miller
Classic Products, Inc.
8/5/2007
It would still help in that it would act as a vapor barrier and also would minimize heat migration into the attic. The warranty you have should include the paint finish on the panels, and who is ultimately responsible for that.
Guest User
1/22/2008
This sounds like a similar problem I am having. We have a metal roof with no decking. The metal is screwed to our slates. We do have condensation and I have been given lot's of suggestions but I am wondering and hoping that a spray foam insulator might solve this problem instead of taking up my whole metal roof. Will a spray foam do it?
Todd Miller
Classic Products, Inc.
1/26/2008
Close cell spray-applied polyurethane.
ila martinez
2/18/2009
we are putting up a metal building and we want to have sealer put in between panels so we can seal the dirt and light out. there is a fome or a tape putty what do you recommend to use?
Nate Libbey
2/19/2009
A Butyl sealant tape (it's kind of like caulk on a roll) it probably about the best way to go.
Todd Miller
Classic Products, Inc.
9/24/2009
Thanks Nate
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