Insulating a flat ceiling in conjunction with a hot roof?
tzrider
| Posted in Energy Efficiency and Durability on
Hey there… My 950 sq ft. house has a hot roof insulated with 4.5″ of spray foam. The roof system is 2×8 rafters with 2×6 collar ties. The attic space is basically a crawl space. I’m planning by adding insulation to the flat ceiling using 5.5″ of rock wool. I currently have zero moisture issues in the house and heat with wood, generally keeping the house humidity pretty low. Am I doing anything bad by adding the insulation to the flat ceiling?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Todd,
Q. "Am I doing anything bad by adding the insulation to the flat ceiling?"
A. No.
That said, I hope you used closed-cell spray foam rather than open-cell spray foam. For information on problems in homes with open-cell spray foam installed on the underside of the roof sheathing, see these two articles:
High Humidity in Unvented Conditioned Attics
Open-Cell Spray Foam and Damp Roof Sheathing
Thanks for the quick reply Martin. Closed-cell foam was used. I'll check out the 2 articles for my own edification.