Ask A Builder
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 am going to dig up my foundation this summer so I can put on outside foam insulation.
Do I need to clean off my foundation in any way?
How far down should I dig? How long will the ground be frozen?
If the foundation has not been waterproofed or the product that is installed needs some touching up, then clean the area thoroughly. In the case of cement block or cast-in-place concrete, cleaning will probably involve hosing off the foundation, letting it dry, waterproofing it, then adding the insulation. For waterproofing, apply a peel-and-stick membrane or a waterproof foundation coating. Be sure to follow the application instructions carefully. These membranes work well for both new construction and retrofits, but the concrete must be clean first. If your foundation already has good waterproofing, then dig away the dirt, brush off the foundation and place the foam tight against the wall. In terms of how far down you should dig, remember that heat always goes to cold. Where you have a temperature difference inside to outside, you are going to have heat loss. The bigger the temperature difference, the more aggressively the heat will try to escape. The frostline in Fairbanks goes down roughly 4 feet on average.
Some winters, that frostline goes much deeper. Below the frostline, there is an average soil temperature of 32 to 40 degrees. A good practice is to apply rigid foam insulation that is approved for direct burial, all the way down to the footings.
Fairbanks building code requires three inches of thickness for foam below grade (below the soil).
Good resources for finding out when the ground has thawed would be the local excavation and septic companies. They work in locations throughout the area and may be able to help you predict the thawing time for your location. June is usually a good month in which to begin excavation, though if you are on the north side of a hill, in a heavily shaded area, or have wet soils, your ground may behave differently.
Q: Where can I go if I want more information on ground source heat pumps?
There is information on our website (www.cchrc.org) including heat pump resellers in Fairbanks. Also the Department of Energy has a website dedicated to energy efficiency and renewable energy (www.energysavers.
gov.) The site has general information about how heat pumps work and the considerations in installing a system. The Permafrost Technology Foundation website (www.permafrost.org) has several technical reports on the use of ground source heat pumps in permafrostladen soils. As ground source heat pumps grow in popularity, we are seeing more being built in the Fairbanks area. CCHRC is beginning research projects that will look at the effectiveness of ground source heat pumps in our region and should have some preliminary information on our website by next spring.
Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at firstname.lastname@example.org.You can also call the CCHRC at (907) 457-3454.