A drainage plane is the continuous water-shedding layer behind a masonry veneer or siding, typically a membrane or air gap, engineered so any water that gets past the exterior surface runs downward and out rather than soaking inward.
No exterior masonry surface is completely watertight over time, mortar joints hairline, brick is porous, and wind-driven rain finds its way past the face. The drainage plane is the backup system: a water-resistant membrane or an open air gap positioned behind the brick or stone that gives that intruding water a clear path down to the flashing and weep holes at the base of the wall, instead of a path into the framing or sheathing behind it.
This matters more in the Blue Ridge foothills than in drier climates, because we get sustained wind-driven rain and then hard freezes right behind it. If the drainage plane is missing, torn, or blocked with mortar debris, that water sits against the sheathing and freezes, and you end up with rot and spalled brick showing up together on the same wall.
More masonry vocabulary from the glossary.
The services where this term comes up.
Chelo's Brick & Stone serves Hillsville, Galax, Wytheville, Fancy Gap, and Independence, VA. Call for a straight answer and a free on-site estimate.
