Mitigating the Odor from Off-Gassing Spray Foam with Bath Fan in Attic
I have a sealed/unvented attic with smelly, off-gassing open-cell under the roof deck. I’ve engaged the installer for help and I reckon they’ll have to redo the job.
In the interim, I’m keeping the attic at negative pressure with an in-line duct fan exhausting into the soffit. It’s sitting on the attic floor with no intake duct. It has improved the situation by 50-70% and I’m looking to optimize further.
Looking around the web I see a few examples where people claim they’ve mitigated spray foam odor with a simple bath fan mounted high in the attic and exhausting through the roof deck near the ridge.
Wondering if anyone here has experience with this… How many CFMs did it require and is there evidence to support having the intake up near the ridge and not on the attic floor?
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Heh, I have no answers....just commenting that when I saw SPF in the title, I was thinking Spruce/Pine/Fir...and was wondering how lumber would be off-gassing and faulty... Now I understand!
I never made the connection before that SPF Spray Polyurethane Foam or Spruce/Pine/Fir :-) Now that you mention it, I can see some acronym ambiguity here...
Regarding the OP's question, it usually takes very little CFM to maintain negative pressure in a space, but the exact amount you need will be determined by a combination of how leaky the space is (you need to exhaust a little more air than the leaks can let in so that you maintain that negative pressure that you want), and how smelly the problem material is (more smelly materials mean a smaller leak is a bigger problem).
You'll probably have to determine what you need expierimentally, but a bathroom fan may well be enough.
Bill
Hi all, here's an update on my situation. Hopefully this helps others with a similar issue. An $85 Panasonic WhisperValue DC installed high in the attic ridge and exhausting to the outside seems to have fixed the problem.
I had ventilated the attic twice before, but only during cool days. I suspect the fumes had migrated into the open-cell foam (alongside Lstiburek's ping-pong water) and were being driven out only on hot days. The key was having continuous ventilation across multiple hot/sunny days. I may try turning the fan off to see if the vapor returns. If it does I might devise a way to cycle the fan as I really don't want 50cfm continuous exhaust in CZ2A.
After installing the fan, I engaged every possible additional source of negative pressure in the house (bath fans, range hood, and the dryer on air tumble setting) and made a pass around the attic perimeter to check for leaks under the lower edge of the foam. It took two cans of Great Stuff to seal everything I'd found! It was important the new attic fan would get dry make-up air from the living space and not humid air from outside. I think I've succeeded as my attic data logger records the humidity's daily peaks and valleys at the same levels as before.
It is great that you have found a way to live with the smell but now the SPF contractor has zero incentive to remove and replace the defective foam.
One must be careful when looking at temporary solutions as if they happen to work they tend to become permanent.
Walta
So a number of people were saying the foam may not be continually off-gassing and thus may not be defective. The hypothesis is these gasses were left over from the original installation. They've been migrating in and out of the foam for months and now that they're gone, they're gone. The true test will be when I get up there and disconnect the power from the fan for a few days when it's hot and sunny.
I would be cautious with that idea. sounds like you have the right approach and I hope it works out for you. I had a roof deck done about 10 years ago and never was able to get rid of the smell. Even after the room was finished it would start to smell on hot days. I have since sold the house but I lived with it for years. best of luck to you