My home was built in 2017 and has Accella open cell spray foam in the unvented attic. In spring & summer 2018 we noticed a mild chemical smell coming from the attic on hot and/or humid days. It would enter the 2nd floor living space through the seams of the pull down attic door. It is a mildish sweet chemical smell. Unpleasant but not massively so. It is stronger when standing in the attic.

In the fall/winter the smell is gone from the living quarters. Even standing in the attic during winter the smell is very faint. Still there, but so faint that it isn't offensive.

It is now Spring 2019 and the smell is back again. The strength of the smell seems identical to last year. That is surprising since I figured it would have off gassed by now.

I noticed a large chunk of foam had fallen to the floor so i placed it in a large ziplock bag and sealed it. A few hours later i opened the bag and smelled the air inside. I did not notice any odor. I then took a saw and cut the piece in half and placed the cut piece to my nose - no smell. Maybe the odor is coming from only certain sections of foam?

I'm concerned about this off gassing and that it hasn't gotten better nearly 2 years after this home was built. The only thing i can think of is to ventilate the attic by forcing air up there and exhausting air from a 2nd floor window.

What could be causing this smell and how can i solve this problem?

  • Vent the attic. Push air thru there like crazy all summer. I replaced my attic entry panel with a panel with a strong fan on it. Get a fan with bearings, not bushings. They're the more expensive variety. However, mines been blowing trouble free for 20 years. Every couple years, I blow the dust of the blades with a shop-vac. – Wayfaring Stranger Apr 21 '19 at 2:42
  • Our attic is sealed to the outside. It is unvented. So if I force air up there it’ll have nowhere to go and have to go back down the entry panel. But I can force air up there and cause the stale attic air to mix with the 2nd level air and exhaust that out of the house. Do you think this is a good strategy? – bradforj287 Apr 21 '19 at 3:54
  • What part of the world seals attics? It must reach oven temps up there during summer. – Wayfaring Stranger Apr 21 '19 at 5:37
  • Unvented attics are common now with new construction and home renovations. See constructionspecifier.com/… – bradforj287 Apr 21 '19 at 14:14
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    Attics get insanely hot - 85C in Phoenix, that's too hot for any readily available electrical wire to be used safely. Is there an intentional strategy to bottling air up there (and thus heat) and not venting it? You wouldn't need much venting to chase away that smell, a muffin fan could get it done (muffin=fan on the back of a PC power supply). – Harper - Reinstate Monica Apr 21 '19 at 16:41

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