Renovating Your Basement Part 2

Preparing the Space

Foundation walls

To prevent heat loss to the surrounding earth, most jurisdictions require exterior basement walls to be insulated for most of their height. Although builders usually place the insulation on the inside face of the foundation wall and cover it with gypsum board, it would be better to place water-resistant insulation on the exterior face where it can keep the foundation warm. If the wall is warm, the dew point, the point at which air vapour condenses as water, occurs on the exterior of the foundation wall where condensation will do no harm.
When insulating the foundation on the inside, you should expect some moisture to condense on the inside face of the foundation wall. Place a moisture barrier, such as vapour-permeable building paper, on the interior face of the foundation from exterior grade to the bottom of the wall to prevent this moisture from wetting the insulation. The top of the wall and the space between the joists should be insulated, because it is here that most of the basement heat loss occurs. Cover the warm face of the insulation with a polyethylene vapour retarder and seal with caulking where the polyethylene meets the floor, walls and ceiling, and at all laps to prevent moisture from getting into the wall. Consult the building code for your jurisdiction for your basement insulation requirements.

Floors

Dampness and cold can enter a basement floor from the ground beneath it. Building codes require an occupied basement in a new house to have a moisture barrier, such as polyethylene, beneath the slab. If you have an older house with no moisture barrier below the floor, consider placing polyethylene over the existing floor before installing the finished flooring. If space and headroom permit, you might also install water-resistant insulation, such as extruded polystyrene, beneath the finished flooring to obtain a warmer floor.

Putting the Systems in Place

Canadian houses contain mechanical and plumbing systems that contribute to our comfort and health. The National Building Code of Canada (NBCC) sets minimum standards for water and waste piping in kitchens and bathrooms and for heat and ventilation in habitable rooms. All new NBCC “Part IX” residential dwellings and small buildings that are supplied with electrical power require mechanical ventilation, to ensure a continuous and adequate fresh air supply. The ventilation capacity required of exhaust appliances for kitchens and bathrooms is set out in Section 9.32.3 of the NBCC.

Air circulation

Excessive humidity and insufficient air movement contribute to two common problems in basements: mold growth and stale air.
Once you have repaired sources of water entry, you may put in heating and air circulation to make the space comfortable. Electric baseboards supply heat, but provide no circulation. If your house has a forced-air heating system, the furnace can provide heat and air circulation to the basement. Most furnaces provide circulation by pushing heated air out of registers and pulling cooler air into return-air grilles. The supply registers should be close to the floor in all rooms to allow the room air to mix effectively and should be near cold surfaces, such as windows.
Return-air grilles should also be located near the floor in all rooms, except the furnace room, to remove the layer of cooler air that tends to collect there and ensure proper air circulation.
Providing your basement with a heating and ventilation system that equals the one in the rest of the house should improve air quality and comfort during the heating season. But what about the period when the furnace is off and there is no air movement?
Photo by: John Burrows
Figure 5 Heating plenum disguised as a lighting fixture

Mechanical ventilation

It is advisable to run the furnace fan year round, or use a furnace cycling device to circulate the air throughout the house. Because fan operation consumes energy, consider replacing a conventional furnace with one equipped with an electronically commutated motor (ECM). This will enable you to select the fan speed to suit your airflow needs and conserve energy. Opening windows usually increases humidity during the warm season, because this is the period when the outside air contains the greatest concentration of moisture. Dehumidifiers and air conditioners are more effective at drying and cooling indoor air during the non-heating months.
A heat recovery ventilator (HRV) is a valuable addition to a ventilation system, because it can exhaust stale air to the outside and replace it with fresh exterior air. The fresh air recovers heat from the exhaust air, then mixes with the house air and is heated and circulated by the furnace.
The stale air in most of our houses is exhausted by the kitchen and bathroom fans, and replaced by fresh air leaking in through cracks and openings. This results in drafts, heat loss and uncertain air quality. A properly designed and installed HRV system can correct these problems in the basement and throughout the house.
It is common for occupants to not use, or to disable noisy bathroom and kitchen fans. This leads to higher relative humidity and increased concentrations of volatile organic compounds (VOCs) in the air. Rather than compromise your air circulation, consider replacing a noisy fan with a quieter model. For more information, see the About Your House fact sheet The Importance of Bathroom and Kitchen Fans.
In some jurisdictions, the fan can be connected to the light switch so that it operates when the room is in use. More information on VOCs can be obtained from Health Canada.