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I'm having some issues with a smell coming from my attic on warm days that exceed 70 degrees. The hotter it gets outside, the stronger the smell is. I think the issue is being caused by a lack of ventilation due to a poor spray foam job. Here are the details.

I have a 1,200 square foot Cape Cod home located about an hour north of New York City. The was built in 1951 and the attic was converted into two bedrooms a number of years later. Back in 2008, a year after I bought the house, I decided to go with Icenene open-cell spray foam when gutting the upstairs bedrooms because so many of my neighbors with the same home had an extremely difficult time keeping the upstairs bedrooms cool during the summer. The spray foam was applied directly to the roof decking and the roof was converted into a non-vented roof. The spray foam, along with adding a return vent in each bedroom, has allowed both the main floor and the upstairs to stay within 2 degrees of each other at all times as long as I keep the fan in the furnace running at all times.

The Smell:
I have done extensive reading with regards to the dangerous smell coming from improperly mixed spray foam. This does not appear to be my problem. The foam was installed 6 years ago and no one in my house has ever been sick. The smell is only apparent on hot days or warm days when the whole house is closed up. If the central air is turned on, then we really don't notice the smell even when the outside temps are in the 90s.

Initially the spray foam applied to the roof decking behind the knee walls was left exposed. Once I found out that the building codes changed, I installed 1/2" sheetrock against the roof rafters that have been taped and painted. This helped with the smell, but it hasn't gone away.

I then called in a home inspector and he performed a blower door test. We determined that the smell was coming from the openings in the second floor ceiling where ceiling fans and smoke detectors had been installed. Since then, I have caulked every electrical box in the upstairs ceiling. The smell lessened.

Based on the amount of air that we could feel rushing through the electrical box for one of the smoke detectors, the inspector and I feel that the spray foam installer did a poor job applying the foam. Either air gaps were never filled properly during installation or the foam may have been mixed improperly causing shrinking to occur and gaps in the envelope to develop.

The Plan:
To me, the smell I'm noticing doesn't smell like spray foam. I reminds me of the smell of old wood studs from when I gutted my house during the first hot summer we owned it. I think the wood from the roof rafters or the roof decking is heating up and that hotter air is expanding into the rooms below the peak of the roof.

I have a feeling that gaps in the spray foam envelop are allowing outside air to get trapped in the peak of my roof. I think the trapped air is heating up due to the black roof and because the dead space between the insulation at my roof's peak is not coming in contact with cooler, conditioned air from the bedroom.

Keeping in mind that my roof is currently unvented, I am seriously considering venting just the peak of my roof. I would have to remove the top two feet of shingles and roof decking closest to the peak. This would allow access for the spray foam in that area to be removed. I would then have to insulate the upstairs bedroom ceiling with either spray foam or fiberglass batts. New gable vents would be installed on both sides of the house while an electric or solar powered fan would be installed close to the peak towards the center of the house. This would pull fresh air in through the gable vents and push out stale air from the fan.

I am attaching a couple pictures to help with my explanation. One is of the storage space behind the knee walls. Spray foam has been sealed, but the floor joists and knee wall studs are still exposed. The other picture is a sketch of my current spray foam application and what I'd like to do next.

I would really like to hear everyone's opinions and suggestions before I hire someone to work on the roof. As you can tell from what I've written, I have done a lot of reading and targeted problem solving to fix this issue. But at the end of the day I am not a professional and I'll take as much advice as I can get.


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Wow, interesting thread! I'm from Connecticut and also have a Cape built in 1956. My upstairs is cold in the winter/hot in the summer. I currently have Rockwool insulation but have been debating spray foam. Do you mind if I ask the approximate cost?

Regarding your attic venting idea - my house has the insulation along the sides and over the top of the bedrooms (like your 2nd diagram). I have two gable vents at the peak (one on each side) and a ridge vent at the top of the roof. From what I've read you don't need an attic fan if you have proper venting. I'm sure a few of the more experienced insulation guys will chime in with your best options.

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I can't really help with your plans but wanted to add that during warm/hot conditions the cooler air inside the house will exit lower leaks allowing or pulling the warm air in the upper leaks. It is often referred to as a reversing of the stack effect.

If you go back to the gable vents you might want to consider a ridge vent in combination as opposed to or along with a small fan. Emphasis on small as most attic fans are sized for an entire attic volume.

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