Common roofing term explained by Capital Construction of Cambridge MA:Vapor retarder
This term refers to a material that is installed on the roof to impede or outright prevent the movement of water vapor through the roof's assembly. It can help reduce ventilation problems in the right installations.
Cambridge roofing FAQ:Should attic insulation systems be optimized along with the ventilation systems?
While ventilation is important on its own, homeowners should be sure to address insulation problems as soon as possible as well. When the insulation components are not taken care of, homeowners will need to deal with frost and moisture problems on the inside and outside of their roofing system.