Q.I have customers who want me to build a log home that will be used seasonally, for about two months of the summer and another two months in the winter. During the rest of the year they want to leave the house closed up and unheated. We’re at the edge of the Rocky Mountain Front Range in eastern British Columbia, and winter temperatures often fall to –20°F. I’ve discouraged the clients from installing a hydronic heating system because of the difficulty of draining it twice a year (draining the domestic water will be headache enough), but what other potential problems should I be thinking about? I’m concerned that the radical swings in temperature could damage interior finishes.

A.Don Fugler, a senior researcher with the Canada Mortgage and Housing Corp. in Ottawa, Ontario, responds: If you leave a house deserted in winter, the biggest risks are to finishes and furniture due to cold temperatures and extreme humidity (high or low). The safest, most convenient way to minimize problems is to provide a modicum of heating. Keep it to about 50°F (10°C). If you build an energy-efficient house with good solar gains, the heating costs for the unoccupied winter periods will be low, and you will avoid the inconvenience of draining plumbing and removing all water-based stored foods and supplies. A small amount of continuous ventilation is also useful for keeping the air fresh. (I agree that a hydronic heating system might be risky in this situation.)

If your customers are intent on leaving the house unheated, there are some precautions I would recommend. Ventilation is particularly important. Running an efficient set of fans (a ducted HRV, for example ) continuously at low speed will mix air and keep the house fresh. Also, you do not want solar gain in an unheated house, because temperature swings can cause condensation problems. If possible, minimize solar gain by using exterior shutters on at least the south and west windows. Before the owners reoccupy the house in winter, they should have someone bring it up to temperature slowly over a couple of days. I would not use the no-heat strategy during the first winter after construction, because there may still be significant moisture in the concrete, drywall, and lumber. A cold or freezing house with high internal moisture is a recipe for trouble.