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On recommendation, we just put spray foam in an un-vented attic crawl space above a porch-style addition to an old home -- we sprayed the L (bottom and side-wall, not the underside of roof). The existing space was poorly insulated and caused ice-dams. I just peeked in the hatch and it was roasting hot in there (hot summer day here). Is the lack of ventilation a problem? There is no good way to vent this space (unless through the roof??) Do I need to worry about excessive heat or fumes building up in that space?

  • Are you worried about fumes killing the bugs? It'll get hot with no ventilation, for sure. You could experience some heat transfer through the wall into your living area. What part of the country are you in? If you're in the southeast or even the northeast, you probably have moisture-control issues that somebody in the southwest won't have to deal with, for example. – Craig Jul 2 '17 at 21:19
  • I think you are on to something about the venting. – SDsolar Jul 2 '17 at 22:06
  • I was kidding about the bugs. Venting with a small, flat roof vent would be easy, but it may or may not be beneficial. :p I do think that in this case, talking to local builders and inspectors is a good idea because the climate just isn't the same everywhere and it can make a difference. I'd talk to more than one builder and inspector just to see which opinions are most widely held by the pros in your area. – Craig Jul 3 '17 at 22:46
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If you had sprayed the entire space including the underside of the roof it would have helped to prevent heat transfer from the outside and no ventilation would be needed.

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    The sun shining on that section of roof is still going to cause a fair amount of heat gain. The solar cconstant is 429.7 Btu/sq. ft./hour. The more insulation you have all around the inside of that space, the slower the heat transfer will be, of course. – Craig Jul 3 '17 at 18:56

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