Open-cell foam in unvented attic, Zone 1
I am a homeowner and have been doing a lot of reasearch on the topic, but could use some assistance with regards to insulation options.
We are building a new home in climate zone 1 (Dallas/ Ft Worth, TX) and my builder is using open cell (icynene) in the walls. The walls are 2×4. They are using OSB sheathing, which then gets wrapped in tyvek. The tyvek will then have a rock or brick aplied for its exterior finish. Are there any issues with this combination? Im a little concerened about the use of OSB. My builder told me that i shouldnt be concearned.
The bigger issue is….. I enquired due to cost savings about foam in the attic and my builder offers an unvented attic option. The process includes spraying open cell icynene to the underside of the roofline (2×4 OSB sheathing to fill the cavity), then “shaving it flush. When my builder does unvented attics they provide a fresh air supply system. He said the purpose of the system is to provide fresh air into the home. due to the tightness of the home the air can become stale. The roof will have felt paper and asphalt shingles. No use of venting/cooling for the shingles. I believe that is called a hot roof if that is important to know.
My big concern is the use of OSB for the roof sheathing, (i double checked this combination and he will be usimg OSB) from what i understand can absorb moisture/humidity faster than what the open cell foam can disperse it. (Read about it on this website) When i questioned him about the humidity that comes from the master bath, laundry room, kitchen, a simulated 180 gallon fish tank, etc… and then the moisture making its way to the OSB, he said the HVAC system would be able to control that humidity. I dont know about that. Your thoughts? I think I would prefer a dedicated humidty regulator/dehumidifier for that purpose. But not sure if it is even required. What is acceptable humidity in an attic with open cell?
Lastly, can anyone provide if a whole house fan/Attic fan would be okay in my situation. I am considering installing a window at the opposite end of the attic from the attic fan. Im thinking of opening that window in the cooler months and using the whole house celing fan to cool the home. Again, a little concerned about the humidity/open cell/OSB combination. Maybe this is a horrible idea.
If i choose not to go with the unvented attic option then an attic lid option is called for where open cell icynene is sprayed to the attic floor along with a bunch of blown in cellulose. And then the attic is made vented by the use of open vents in the gables and soffits. Radiant barrier roof sheathing is also provided. My HVAC in either case of course will be located in the attic.
Thank you for reading and i look forward to the responses.
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