d7e42f72_ES__INC____Roofing_Terminology__VALLEY
(1) A sheet material designed to restrict the passage of water vapor through a roof or wall. In the roofing industry, a vapor retarder should have a perm rating of 0.5 or less; (2) Roof component designed to obstruct water vapor flow through a roof or wall. See VAPOR RETARDER. [VALLEY] 
VAPOR BARRIER
ARMKO INDUSTRIES, INC. - Roofing Terminology
VALLEY