Crawlspace Best Practices
Crawlspace building practices have changed dramatically over the last 50 years.
Best practices for crawlspaces used to centre around keeping the crawlspace well ventilated to keep moisture at bay. These methods involved using gravel, road crush, or washed rock for drainage, installing vents around the exterior to allow airflow, and insulating the floor space between the living area and the crawl space.
Over time, it was discovered that simply ventilating a crawlspace poorly mitigates the moisture and mould. Eventually, those building practices turned 180 degrees to what they are today. There was also always a concern about pipes freezing. Pipes would have to be heat traced and insulated, but insulation could become damaged, and heat tracing could fail at the most inopportune times.
Now the best-known practice for crawl spaces is to create a conditioned space that is sealed and insulated to the home’s exterior and is heated. Think of it as the same way we treat any basement space now.
Crawlspaces should be heated to create a conditioned space under the flooring. It usually can be reasonably straightforward to install a heat duct or two into the crawlspace. Heating the area under the floor does several things. It keeps the floor warm, keeps moisture levels down, and prevents plumbing from freezing.
Remember that whenever you heat a space, you also need a return air path back to the furnace. It’s tough to blow air into an area without a place for air to escape! Try to install the heat source at one end of the crawlspace, and the cold air return at the opposite end.
Insulating the crawlspace walls keeps the space warm to protect pipes from freezing and keeps upper-level floors warm. Framing with batt insulation, foam board panelling such as EPS or XPS, or spray foam are all great ways to insulate the perimeter of a crawlspace. Make sure the insulation is at least an R-12.
Ensure any framing is not in contact with the ground unless it is Permanent Wood Foundation (PWF) material, rated for long-term ground contact.
The best kind of batt insulation to use is mineral wool (Roxul/Rockwool) insulation. Mineral insulation has a higher R-value per inch, is stiffer than fibreglass (making it easier to install), and is water- and fire-resistant.
Do not insulate under the floor. If there is insulation or a vapour barrier already there, remove it so the heat can warm the floor above!
Crawl spaces need to be adequately sealed to keep moisture out and humidity levels down. Doing this helps to prevent the formation of mould and mildew. Crawlspaces also need to be sealed to be energy efficient.
Typical best practices include sealing the floor with a minimum of 6-10 mil polyethylene sheeting (vapour barrier), sealing the foundation walls, and sealing joints with Tuck tape or acoustic sealant.
Try to have the access hatch to the crawlspace located inside of the building. If the crawlspace access hatch needs to be located at the exterior of the building, don’t forget to insulate and seal it. Make a way for the hatch to latch tightly and install some weatherstripping to make a tight seal around the perimeter.
If utilities such as a water heater or furnace are located in the crawlspace, it is best to install sealed units with powered vents that draw their combustion air through a dedicated vent directly into the appliance. These are also known as “high-efficiency.” A combustion air intake will also have to be installed if a low- or mid-efficiency furnace is installed. A combustion air intake is essentially an insulated open pipe to the exterior of the building that terminates next to the furnace. If you have this type of system, consider installing an automatic damper on the combustion air intake pipe. This type of damper opens automatically when the furnace calls for heat and closes when it turns off.
Taking steps to keep moisture out and heat in will help your crawlspace last longer, prevent mould, and increase comfort in the building. It will also increase energy savings. It may take a little crawling around, getting dirty, and a bit of cussing, but you’ll be thankful you did!