Should I Insulate My Crawl Space?

Chuck asks,

My house has a crawl space. The walls are insulated; there is a vapor barrier on the dirt floor as well as the concrete foundation walls. We are on a well and the pressure tank is located in the crawl space along with plumbing supply and drains.

We have wood and ceramic floors, which do get cool – especially in the winter. The temperature in the crawl space during the winter months can go as low as 34 to 36 degrees. I would like to insulate the floor, but my concern is that if I insulate it I will lose the heat that does radiate from the living area to the crawl space, and then my plumbing might freeze.

My heat source for the house is a gas fired Monitor heater. The home is located in Alaska so winter is long and the temperatures in our area can go as low as -35 degrees for 2 to 3 weeks or more at a time.

Our Answer

Fifteen to twenty percent of heat loss in homes occurs through floors, so a few changes will make a big difference in your comfort – and your energy costs.

I recommend insulating your crawl space floor with fiberglass batts as thick as the floor joints are deep. So if you have 8-inch joints, use 8 inches of insulation. The insulation should be unfaced – no foil face, no paper face. It can be supported in place by insulation hangers, which are essentially wires inserted between floor joists. They flex like springs, and are sharp on the ends so they can pinch into the joists and hold up the insulation.

As for the plumbing, you should insulate it using fiberglass tubes. They’re pre-made and are designed for the specific size of pipe (for 1-inch pipes, use 1-inch tubes, etc.). Make sure to use insulating tape to seal the edges and corners, and the result will be a far warmer floor this winter.