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Brad Jones Posted: Jun 11, 2019 01:28 AM	Odor in attic only on sunny summer days. Could this be spray foam or something else? My home was built in 2017 near Boston MA and has Accella open cell spray foam in the unvented attic. In spring & summer 2018 we noticed a smell coming from the attic on hot sunny days. It would enter the 2nd floor living space through the seams of the pull down attic door. Standing in the attic the smell is very strong. I have determined that the major factor is the temperature of the sheathing. In the summer sun the sheathing can hit over 120F. If I blow all the air out of the attic w/ a portable duct fan I observe new odor generation so long as the sun is shining. Once the air is exhausted, barely any odor is detected during summer nights. The house is aligned east/west. The east sheathing heats up in the morning and the west side heats in the afternoon. I have confirmed that both sides are generating odor in equivalent amounts. In the fall/winter the smell mostly disappears. Even standing in the attic the smell is very faint during this time of year even if the sun is shining. Still there, but so faint that it isn't offensive and smells more like a normal new construction smell. This makes sense since the strength of the sun is much less so the the odor causing material isn’t heated nearly as much. The sheathing is nowhere near as hot. It is now Summer 2019 and the smell is back again. It’s hard to describe what the smell is. It is similar to fresh paint with a woody/lumber element to it. It doesn’t smell purely chemical and doesn’t smell purely organic. Kind of a mix of the two. And I don’t think it is “fishy” smelling. The odor also has a unique “moist” element to it and almost makes the room feel more humid than it is. The odor also sticks in your nose for a little bit after. What could be causing this odor? The Foam? Roofing materials such as felt or ice & water shields? I did find an isolated piece of foam that had fallen to the floor. I placed it in a bag and after 5 hours tried smelling the inside of the bag. No odor. I even cut the piece in half and smelled the inside. No odor and the foam seemed normal.
Brad Jones Posted: Jun 11, 2019 01:28 PM	Well maybe the sun correlation isn't so strong. It is gloomy today with lots of rain and the smell is back in the attic pretty strong. Underside of the attached garage (with no spray foam) is only 76 degrees.

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Brad Jones

Posted: Jun 11, 2019 01:28 AM

Odor in attic only on sunny summer days. Could this be spray foam or something else?

My home was built in 2017 near Boston MA and has Accella open cell spray foam in the unvented attic. In spring & summer 2018 we noticed a smell coming from the attic on hot sunny days. It would enter the 2nd floor living space through the seams of the pull down attic door. Standing in the attic the smell is very strong. I have determined that the major factor is the temperature of the sheathing. In the summer sun the sheathing can hit over 120F. If I blow all the air out of the attic w/ a portable duct fan I observe new odor generation so long as the sun is shining. Once the air is exhausted, barely any odor is detected during summer nights. The house is aligned east/west. The east sheathing heats up in the morning and the west side heats in the afternoon. I have confirmed that both sides are generating odor in equivalent amounts.
In the fall/winter the smell mostly disappears. Even standing in the attic the smell is very faint during this time of year even if the sun is shining. Still there, but so faint that it isn't offensive and smells more like a normal new construction smell. This makes sense since the strength of the sun is much less so the the odor causing material isn’t heated nearly as much. The sheathing is nowhere near as hot.
It is now Summer 2019 and the smell is back again.
It’s hard to describe what the smell is. It is similar to fresh paint with a woody/lumber element to it. It doesn’t smell purely chemical and doesn’t smell purely organic. Kind of a mix of the two. And I don’t think it is “fishy” smelling. The odor also has a unique “moist” element to it and almost makes the room feel more humid than it is. The odor also sticks in your nose for a little bit after.
What could be causing this odor? The Foam? Roofing materials such as felt or ice & water shields?
I did find an isolated piece of foam that had fallen to the floor. I placed it in a bag and after 5 hours tried smelling the inside of the bag. No odor. I even cut the piece in half and smelled the inside. No odor and the foam seemed normal.

Brad Jones

Posted: Jun 11, 2019 01:28 PM

Well maybe the sun correlation isn't so strong. It is gloomy today with lots of rain and the smell is back in the attic pretty strong. Underside of the attached garage (with no spray foam) is only 76 degrees.

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