Foam insulation and how and what to Insulate
To the home insulation experts…
I live in San Antonio, Tx, Zone 2B, in a 22 year old, 2-Story home. I currently have between 8-10″ of blown-in, 22 yr old insulation in the attic. The attic has soffits, ridge vents and a brand new roof. The attic also hosts my upstairs and downstairs air handlers for my electric heat pumps. The attic gets extremely hot in the summer. To me… It makes sense to try and reduce the heat in the attic, to ultimately and hopefully reduce my cooling bills in the summer. To lower the temperatures in the attic, I am considering spray foam on the underside of the roof decking, which is also OSB…
Before I choose spray foam, I’d like a better understanding of the questions and expectations I should have from the vendors.
1. If I choose spray foam insulation, should I expect the existing venting to change? I don’t believe I’d want to close off any existing(ridge vents & soffits) venting…. Do I need to, or should I?
2. Do I need to be concerned with moisture, in San Antonio, which has higher humidity that most expect, in the attic if I have spray foam installed?
3. Open Core or Closed Core? Most of what I have read has denigrated Open Core, but are their use cases to which Open Core makes sense in my locality?
What questions haven’t I considered?
Many thanks,
Joe
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Replies
If the attic is vented and unconditioned, I'm not sure what the benefits vs costs of insulating the roof deck are. I guess you reduce the radiant heat transfer from the hot roof, but the attic space will still be exposed to outdoor heat so will, at a minimum, reach ambient temps. Seems like not a lot of payoff since spray foam is so expensive. Or maybe you're proposing to close-off the attic? I think there are lotsa articles on that.
https://www.greenbuildingadvisor.com/article/creating-a-conditioned-attic
https://www.greenbuildingadvisor.com/article/pondering-an-attic-conversion-in-new-york