Crawl space

Published on July 26th, 2012 | by Henri

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Insulating a crawl space

Q.    We will be replacing the insulation in the crawl space of our secondary home which is located 20 feet from a lagoon. We’ve had major renovations and an addition done to the home so the original insulation has been abused by the contractors and left hanging. What type of insulation (encapsulated or not) would you recommend for this type of environment?

A.    It is usually better to insulate the walls of a crawl space than to insulate between the floor joists above it. This is also easier to do and it makes the space part of the heated and air-conditioned envelope. However, it is essential that the crawl space floor be covered with 6-mil plastic at minimum (if you can find heavier plastic in agricultural stores, by all means use it). The plastic needs to cover the entire crawl space floor and be made tight around the perimeter by weighting it down with bricks or pressure treated wood, or by burying it in a band of soil. If there is any risk of leakage into the crawl space, the plastic should be brought up the foundation walls to a point above the grade and taped to the walls. This will prevent water from getting on top of the plastic where it could only evaporate into the crawl space and cause problems.

Where the plastic sheets are joined, be sure to overlap the joints at least two feet and tape them with duct tape.

To protect the crawl space from leakage, be sure the grade around the foundation slopes away from the house to allow for positive drainage from the roof, snow melting and rain.

For insulation, use rigid extruded polystyrene and adhere the panels to the foundation walls with a compatible adhesive such as StyroBond or polyurethane caulking.

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