Unoccupied Basements and Crawl Spaces

Factors that are considered when determining if a crawl space is to included in the thermal envelope include climate, ground dampness, and the presence of ducts and pipes within the space.

The most important practical consideration affecting the decision to include or not include is the ease and cost of air sealing and insulating the floor versus air sealing and insulating the foundation walls. If there are many pipes and ducts that run under the floor, it is typically best to include the crawl space in the envelope. It is generally much easier to install perimeter insulation than floor insulation, unless the perimeter is not level and semi-smooth to work with.

Not currently approved for DOE grant money but on the rise is masonry block insulation. This process involves injecting 2-part foam into the masonry cores of block. It can be pushed up to 12 courses and expands to fill the empty core. An average 8" block can be brought from approximately an R2 to an R8. With at least 2 courses typically exposed above grade, this greatly keeps the temperatures out of the envelope.

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