Cottage Q&A
QUESTION
We recently added on to our seasonal cottage and decided to build our addition on a concrete block basement. The basement subcontractor told us we had to heat it to prevent damage from freezing. Is this true?
Phil Osfolk, Blackstone Lake, Ont.
ANSWER
Any time soil and concrete live beside one another there is the possibility of the foundation being damaged during a freeze. Soil deeper than about two metres naturally maintains a temperature of 9°C, or 48°F, even in winter. When basements are not properly insulated or heated, warmth from the soil can be transferred into the colder building. In the simplest of terms, this heat loss allows the water in the soil to freeze, thereby creating pressure that can bow your foundation inward or heave the entire structure upward. The process can cause cracks or greater damage.
Some soils are less susceptible to freezing or frost-heaving, but if you are building in earth containing fine sand or silt, you are especially at risk.
Ensuring your basement is above 5°C will reduce the likelihood of frost damage, not to mention help keep your basement materials drier, reducing the potential for unpleasant odour and mould. However, according to Kim Pressnail, an associate professor of civil engineering at the University of Toronto and an expert in frost-heaving soils and foundations, simply heating the basement may not be the most efficient solution. It may be cheaper in the long run to stem the heat transfer through the basement wall by covering the exterior of your block foundation with thermal insulation, such as Styrofoam.
Steve Brearton
Published in the June 2007 issue of Cottage Life.
