High humidity and smell in spray-foamed attic
Hi – I am really hoping someone can help me out. I have seen similar topics posted, but no solution.
We had the roof deck of our attic (which is also our second floor – a cape cod style house) sprayed with Covestro (formerly Bayer) Bayseal Open Cell foam. The foam seemed fine for a few months until the summer hit. With the return of hot humid weather, we started to see very high humidity in the attic spaces behind the knee walls. On hot sunny days, there is also a distinct unpleasant smell on the second floor.
The attic spaces start out in the early morning at the same temp (72 degrees) and humidity (low 40s) as the house. There is almost no smell except for a typical attic smell. Around noon, when the sun hits the front of the house, the humidity shoots up into the 60s or 70s. This is when the smell starts. At first it only smells in the attic spaces behind the knee walls, but by 5 p.m. – it smells throughout the second floor. As the sun sets, the humidity and odor start to drop and by morning they are normal again. And then the cycle restarts. The smell and humidity are not as strong on cloudy or rainy days – so the sun must play a role.
I have read a bunch of these topics – so I will go ahead and answer as many questions upfront:
– We are in climate zone 4.
– The attic has 5.5 inches of Covestro (formerly Bayer) open cell, although some small areas look like they might have only 3 inches.
– The basement is sealed and dry. 40% RH
– We do not have plants, dry clothes inside, or do anything else that would create excessive moisture. All the fans (shower, stove, and dryer) are new as part of a renovation and do not vent to the attic. The house stays around 45% RH.
– We have had a Covestro rep out who said the foam looks good and on ratio. On a second visit, the rep took samples but we have not heard back yet.
– The HVAC units have all been checked and they are not short cycling and are not oversized. I have read many recommendations to add a supply and possibly a return to control the humidity – but there is not one big attic – it has several small attic areas behind knee walls which would make conditioning them challenging.
My questions are:
– Where is this humidity coming from? I have read different theories on whether vapor drive through the roof cause this situation of “ping-pong” humidity. Some say yes; others no. If the foam was less that 4-5 inches could this be part of the problem? But if the foam was sprayed too thin our problem would be high temperatures – not high humidity?
– What is the smell? The Covestro rep says cured spray foam doesn’t smell and doesn’t off-gas.
– Has anyone had any success in finding a solution to this problem?
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