Insulating your foundation with ease


By CCHRC Staff

The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.

Q: I have a concrete foundation. I heard insulating your foundation can save heat. How can I do that?

Concrete is very conductive, and heat always goes to cold, so a foundation without insulation is basically a bottomless heat sink. If the foundation is un-insulated, there are definitely opportunities to save some heat.

Current code requires an R-value of 15, which is about 3 inches of blue foam.

Ideally, digging out the outside of the foundation and insulating the outside will keep the foundation warmer but doing this type of work on the outside of a home is not always practical. In such a situation, put foam on the interior of the home’s outside walls and tape the joints.

On a similar point, the rim joist area is prone to air leakage where the joists meet the outside wall.

Often, fiberglass insulation is put into joist bays, but that is not enough to stop air leakage. A better choice is to install sheets of foam fitted to each joist bay, then spray foam around the edges.

Another option is to hire a spray foam contractor to spray between the joists.

These techniques will help stop air flow and heat loss through that part of the foundation.

Q: Is there a way to limit the amount of offgassing in my home or ventilate it in some way?

For those who do not know the term, offgassing, or outgassing, is the release of gas from materials over time. Often these materials are plastics or other petroleum-based substances that release chemicals that can be hazardous to health.

For starters, try to use “green” materials that do not offgas hazardous substances like formaldehyde and other volatile organic compounds (VOCs). Low VOC and non-VOC paints, carpets, caulks and glues are available. Furniture and fabrics also offgas, so look for healthy alternatives such as solid wood furniture and other non­VOC products. In new construction, despite the best attempts to use entirely healthy products, there will probably be some type of VOC. Before moving in to a new home, ventilate the home as much as possible. One method is to turn the thermostat up very high, to promote outgassing, and run the ventilation system at high speed for a day or two. This tactic will help “bake out” and vent VOCs.

In older homes, particleboard countertops, shelving and cabinets can be coated with a non-VOC sealant to prevent further outgassing.

Also, use greener cleaning products and store chemicals outside rather than indoors. Try to purchase only as much as needed so unused chemicals do not sit around.

The best way to get rid of offgassed substances is to regularly make sure the home is properly ventilated by opening windows and using mechanical ventilation.

A well-ventilated home will exchange air more frequently, exhaust pollutants and bring in fresh air.

Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at can also call the CCHRC at (907) 457-3454.