Insulating Your Basement

Generally homeowners don’t think of their basement as a prime source of heat loss, yet basements can account for 20 to 30 per cent of a homes’ total heat loss.

Insulating your basement is one of the most important things you can do to improve the comfort of your home and get value for your energy dollar. Before you insulate your basement you need to ask yourself a number of questions.

• Is there any dampness or water leaks?
• If I don’t plan to heat the basement, do I need to insulate it?
• Should I insulate inside or outside the basement and what type of insulating material will I use?
• Should I insulate the basement floor?
• What rebates or financing programs are available for basement insulation?

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

Before adding insulation to the basement walls or the crawl space foundation, and prior to refinishing a basement room, it is essential that you repair any leaks and solve any problems with dampness. Wait until it is thoroughly dry before you install the insulation, to be sure all problems have been eliminated.

Whether you heat your basement or not you should insulate the basement walls. As shown in the diagram, heat loss from the heated area to the basement flows to the outside. This movement of heat reduces the comfort of the heated area, creates an uncomfortably cold floor and increases heating costs.

If the basement walls are insulated, the heat loss to the basement from the heated area is retained in the basement and the temperature in the area will increase.

If you require a significantly lower temperature in the basement, but you want to eliminate heat loss from the main floor, it is recommended that you insulate the basement ceiling. However, insulating the ceiling over the basement will create a cold space. Therefore any exposed pipes, hot water tank or heat recovery ventilation system must be insulated.

If the basement area is to be heated to the same temperature as the rest of the house, there is no need to insulate the ceiling of the basement. The main objective of insulating the basement is to bring this area within the heated living areas of the building and the basement ceiling should therefore be no different from the ceiling between other floors of the house, if the basement is adequately insulated.

If you insulate the ceiling, be sure not to cover the insulation with plastic, tyvek, or any material that does not let water moisture pass through it. Using this type of material to cover the insulation will cause condensation and water build up on the warm side of the material.

It is often easier and cheaper to insulate the inside of your basement rather than the outside walls. However, if your basement has a history of damp or dripping walls you should insulate on the outside.
 

Insulating basement walls on the inside involves the following:

1) A moisture barrier (polyethylene 6-ml) is installed on the cold side of your insulation and serves to protect the insulation from water and moisture coming in from the outside wall. The moisture barrier covers the concrete wall up to the ground level only. The moisture barrier also extends under and beyond the floor plate and attaches to the vapour barrier when it is installed.

2) Frame the wall and install batt insulation between the studs next to the moisture barrier. The moisture barrier protects the insulation from moisture that may come in from the outside.

3) A vapour barrier is installed on the warm side of the insulation and is continuously sealed. It serves to keep moisture in your home from penetrating into the wall cavity. The moisture barrier is sealed to the vapour barrier at the floor plate.

4) Wall covering such as gyproc, wallboard etc. is used to finish the wall.

If part of your basement is a cold cellar or an unheated garage, apply the insulation to the cold wall that separates the heated basement from the unheated space. Treat this as an external basement wall.
 

Insulating basement walls on the outside involves the following:

1. Digging the Trench-The excavation should be down to the footings. Never dig below the bottom of the footings. Since this is a big job, the width of the trench should give you room to work in.

2. Preparing the Surface and Site- First clean the surface of the foundation with a wire brush and scraper. Inspect the foundation for major holes, cracks or damages. Repair where necessary.

3. Applying the Insulation-Three major types of insulation are used on the exterior of basement walls: rigid glass-fibre boards, polystyrene or polyurethane boards. Measure and cut the insulation to the desired height (generally from the top of the footings to the flashing). Start at one corner (overlapping at the corners) and keep the insulation sheets as tight to the walls possible. The insulation is held in place at the top by the flashing and by corrosion-resistant fasteners and washers are used to secure the protective finish.

4. Flashing- Flashing helps keep the insulation in place, prevents water from getting behind the insulation, and provides a clean, neat junction.

5. Exterior Protection- A covering is needed to protect the insulation from sunlight and damage by people and animals. It is applied from the top of the insulation to a point about 300mm (12 in.) below ground level. Some possibilities include: expanded metal lath with cement parging, polymer-modified pargings, pressure-treated plywood, fibreglass panels and vinyl or aluminum siding.

6. Backfilling- The drain tiles should be covered with150mm (6in) of clean gravel and preferably a strip of filter fabric. Backfill in stages, removing large objects, and compacting or tamping the ground. When the hole is finally filled make sure the ground slopes away from the house.

The earth below the basement floor is equivalent to six to eight inches of fibreglass insulation. Insulating the basement floor will increase the comfort in the area. However, you will not see any significant energy savings. If you plan to insulate your basement floor, the greatest gains will occur by adding insulation three feet in from the foundation where the most heat loss occurs.
 

Newfoundland Power offers rebates and financing for basement insulation upgrades in electrically heated homes. Click here for details.