Face Seal

A building enclosure rain control strategy that relies on the exterior face of the enclosure to act as a perfect barrier to rain penetration. This method typically relies on exposed sealants to provide rain tight joints, and hence is highly reliant on workmanship and maintenance to achieve performance. Failure is defined as water penetration of the face. It is a sub-set of perfect barrier rain control strategies.

Face velocity

Is the average velocity of air passing through the face of an outlet or return.


A deficiency in the installation of membranes (roofing, self-adhering membranes, etc.) that results in a fold in the edge of the membrane, through which air and/or water can penetrate.

Flow hood

A diagnostic tool used to measure air flow through ducts, supply registers, and return grilles.

Flow Plate

or TrueFlow Air Handler Meter is a device designed to provide a simple and accurate measurement of air flow through residential air handlers. Flows can be measured between 400 cfm and 2,200 cfm

Freeze Thaw

Damage that occurs to stone, clay, or cementitious products due to high moisture content (near saturation) combined with cycling above and below the freezing temperature. Typically manifested as spalling of the surface.