Insulating Your Crawl Space

There are a variety of sizes and types of crawl spaces. Usually the walls are less than 5 feet high, and made of concrete or wood. Typically, crawl spaces have dirt floors. 

A crawl space can be insulated in either of two ways:

• The walls of the crawl space can be insulated either on the inside or outside, creating a heated area.

• The ceiling of the crawl space can be insulated to keep heat from transferring from the heated space above to the crawl space.

Before you decide how to insulate your crawl space, determine what your plans are for this space and whether these plans will require you to have a heated area or an unheated area.
 

Heated Crawl space

Insulate the walls of the crawl space if it will be used to store a furnace, a hot water tank, water pipes or any item subject to damage in an unheated or damp environment.

First, measure and cut small pieces of insulation and fit them snugly into the header joist. Insulate the interior walls with a rigid insulation, or frame the wall and use either a fiberglass batt or a poly-wrapped insulation. Install no less than R-12 insulation. Use a moisture barrier on the cold side of the insulation and a vapour barrier on the warm side, in the manner same as for a full basement wall.

If there is no moisture barrier on the crawl space floor; add one. The exposed dirt floor is a major source of moisture. Use a 6 mil polyethylene sheet overlapped at the seams and held down with boards, bricks or a layer of crushed stone.

Crawl spaces should be ventilated. The vents should be closed and sealed during the winter and opened during the summer.
  

Unheated Crawl spaces

Insulating the ceiling of the crawl space is only recommended when combined with wall insulation.

First, a vapour barrier must be installed on the warm  (top) side of the insulation unless the floor above is covered with an impermeable material such as linoleum or plywood.  Use polyethylene cut to fit the spaces between the joists or wrap the sheets around the joists and into the spaces.

Install 6 inches of fiberglass batt insulation (R-20) between the floor joists, supported with wire mesh or string stapled to the bottom of the joist.
 

Wrap Up For Savings Program

To obtain more information on insulating your crawl spaces, click here to view Natural Resource Canada's publication “Keeping The Heat In” online or to order a printed copy.