Q&A Spotlight: What’s the Correct Approach to Insulate a Brick Crawlspace in Zone 4A? – GreenBuildingAdvisor

Q&A Spotlight

The walls may not have footings below the frost line, which complicates things

If there were a Building Science Hall of Fame (BSHF), brick would earn an easy first-ballot induction. It’s durable, fire-resistant, and manufactured to consistent quality rather than quarried from nature. Long before concrete took over foundation work, 19th-century builders commonly used brick for above-grade foundation walls. Crawlspaces, however, would be far less likely to make the BSHF. Too often they’re damp, mold-prone, hard to access, and challenging to insulate well—making them a frequent source of building-performance problems.

Recently, member “Imosakow” (whose name is Luke) posed a question that combines the two previously mentioned elements. He writes that he wants to encapsulate the crawlspace of his home on Long Island, NY. The house was built in 1885 on a brick foundation, and he’s convinced that the walls do not extend below the frost line and are without footings.

He says that his goal is to reduce humidity and to prevent the crawlspace from sucking heat out of the first floor. So far, his plan is to add rigid insulation to the brick wall interiors and lay a poly vapor barrier over the dirt floor that extends up onto the walls. He adds, “I’ve read that in cases where foundation walls don’t reach the frost line, adding a horizontal rigid insulation “skirt” across the ground (extending a few feet inward) can reduce heat loss through the soil. However, others suggest this could increase frost-heaving risk for the foundation because the heat loss you prevent might have been what kept the soil from freezing.”

The topic for this Spotlight: How can Luke encapsulate his crawlspace without putting the foundation at risk?

Problems with brick

It turns out there may be other problems associated with brick structures and insulation. Expert Malcolm Taylor lists three:

– The heat may help…