Have a good weep: the unnoticed feature that makes brick walls work
/As noted in the pages of this blog before, when it comes to brick construction, having a cavity can be a good thing. Cavity wall design places a single wythe of brick on the facade of a building and backs it up with a supportive structure of wood or steel studs, concrete masonry units, or some other load bearing skeleton. Between that structure and the brick veneer is an air space of one or more inches that allows any water that penetrates the veneer to flow harmlessly down the back side of the brick to the building’s foundation.
But what happens then? Why does the air space not fill up with water like a tiny but disproportionately deep swimming pool? The key to making the cavity wall system work is a small, unnoticed, and disrespected feature of modern brick construction: weeps.
Can you spot the weep among the landscaping?
Weeps are intentionally placed holes in the mortar between brick units in the veneer. This spot where the ends (or “heads”) of two units meet is called a “head joint.” Virtually anywhere else in a brick facade a less-than-complete filling of head joints with mortar is the cardinal sin of brick masonry, and incomplete head joints are likely culprits for allowing the penetration of water in the first place. Ironically, leaving selected head joints completely open in key locations at the building’s foundation allows penetrative moisture to drain harmlessly back outside.
A closer look. Note the metal flashing that protrudes beneath the weeps. It spans the full depth of the cavity behind the brick veneer to channel water to the openings.
Weeps of at least two inches in height are recommended at 24 inch spacings at the bottom of walls, and non-corrosive metal or plastic vents can be installed to prevent insects from entering through the weeps. Perhaps the greatest benefit of vents, however, is they communicate that the head joints were left open intentionally as part of the structure’s design. Without them, well-meaning but misinformed maintenance personnel may try to seal the weeps in the future. Weeps get no respect.
Weeps also don’t deserve all the credit. Through-wall flashings spanning the entire depth of the wall cavity are a necessity for collecting any moisture trickling down the interior of the wall and channeling it toward the weeps. Weeps and flashings are a dynamic duo that must go together wherever water might collect in the cavity. The bottom of the wall is the most obvious place, but special weep arrangements may need to accompany any feature that spans the interior cavity and creates and artificial “floor” that may collect water, like shelf angles and window sills. A weep without a flashing in these places is useless, and vice versa.
The Brick Industry Association offers guidance on design and workmanship to make sure you don’t weep in vain. Click the buttons to learn more.
