In an article for Spray Foam Insider, Vented vs Unvented Attics: It’s a Communication Thing, Tom Harris, Polyurethane Foam expert, explains the building science of vented and unvented attics.
Specifically, he explains how spray foam contractors can explain to a homeowner, builder or inspector that adding back or leaving insulation on the floor of the attic in a conditioned (non-vented) attic violates Building Codes.
Essentially, Harris explains, we need to ensure non-vented, conditioned attic space is communicating with the conditioned space below, both from a temperature and air movement perspective.
If the building owner requests less spray foam to be installed at the roofline and that insulation be installed on the attic floor, it would block the flow of heat and air into the attic space. In a cool/cold climate, the attic is now isolated from the heat source (the conditioned space below it) because of the insulated floor.
If not enough spray foam was installed on the roofline to stop the cold from getting through the insulation, there is a good chance the inside surface of the spray foam is going to end up below the dew point of the air in the attic – and you’ll get condensation, which is what we try to avoid by installing insulation in the first place.
Read the full article over on Spray Foam Insider.
For more continuing education for spray foam contractors, visit Tom Harris’ PUR Consulting website to take a course.
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