Stucco Failure In Houston Building - Why Air Tightness Matters

Why should we focus on an air barrier? I thought buildings needed to breathe?!

Note the proliferation of mold in the stucco of the north exterior wall. This particular failure was likely caused by a few factors that hinge both on the building’s air tightness and the quality of the stucco installation. In Houston, buildings are air conditioned almost constantly and the gulf coast southeastern winds prevail. So if air leakage is high and the building has a stucco exterior finish, the wind pressure could easily push massive volumes of the cold air conditioned air through the north exterior wall and into the stucco assembly. Once the moisture is in the stucco assembly and cannot move through a drainage plane (note this particular wall’s accessories, i.e. lack of screeds), it’s going to sit there for the fungal colony to begin its empire expansion. There could also be an elastomeric paint used, which are commonly used on stucco, and which could be making things more difficult - hard to tell exactly on this one. Many other buildings in this neighborhood are definitely painted with it. But my favorite feature of the whole building is the random window unit placed just so.

For more info on stucco than you ever imagined, check out our podcast episode on that very topic.