If you convert your vented unconditioned attic to an unvented conditioned attic by installing open-cell spray foam on the underside of your roof sheathing, you may be surprised to discover that your attic is now the most humid room in your house.
Why? We don’t know. Although building scientists haven’t achieved a consensus on the answer, we do have enough information to paint a picture of what’s going on.
Consistent reports from homeowners and builders
Lots of GBA readers have posted reports of this type of problem. Here is a sampling: