I have a cottage, with a basement, that we only visit for perhaps a couple of weekends each winter. We were advised to leave the heat on low all winter, to prevent any structural damage due to freezing and thawing. Is this necessary?
Well, it might be a good idea if your basement isn’t well-insulated. In winter, basements often get colder than the soil surrounding them. (This is because deep soil—more than about two metres—naturally maintains a temperature around 9˚C.) The chilly basement draws warmth out of the soil, the soil becomes cold, and the water in the soil freezes and expands, putting pressure on the basement. This pressure can cause the structure to bow inwards, or heave upwards. The results? Cracks in the foundation, or worse. The more moisture there is in your soil, the more likely this is to happen. As well, some types of soil—such as fine sand or silt—are more susceptible to freezing than others.
If your basement stays toasty, there is less chance of a warm-soil-to-cold-building heat transfer, and therefore, less chance of frost damage. So indeed, one option is to keep the heat on low (above 5˚C). Another is to cover the exterior of the basement with thermal insulation. That’s no small job, but it may be more efficient in the long run.