Insulating and venting a concrete crawl space - November 26th 2001



How should we insulate and vent a concrete crawl space? It is completely closed in and has a skim coat on the floor.

The most important area of the crawl space is the concrete wall. Apply a minimum 1 1/2 inch RIGID FOAM INSULATION to the concrete walls using a foam stick adhesive.

Ventilation should be provided at a rate of 1 square foot for every 300 square feet of crawl space. Vents should be installed in the joist box opening (area between joists) in the ribbon band to the outside. These vents can be aluminum or plastic with a slide closing device. Vents should be kept open in the warm months and closed in the cold months.

An uninsulated crawl space causes cold floors and higher heating bills. To insulate the underside of the subfloor I recommend using a reflective foil product such as REFLECTIX or KRONA. Before applying check to see if there are any water pipes or heating ducts hanging below the joists. These should be insulated with foil duct wrap and/or pipe wrap designed for this purpose.

Starting at the end face staple the foil product to the joists all the way across. Overlap tabs and seal with foil tape to create a vapour barrier. You do not need to wrap water pipes or heat ducts if they are between the floor joists. The reflective insulation reflects cold back to the crawl space and heat back into the cavity of the home.