Is it true that opening a lightly insulated or un-insulated cottage and heating it for brief winter trips can be damaging, since moisture that develops when the building is warmed can be harmful as it freezes? Is damage likely to occur to drywall or insulation?
Typically, the first thing we do on a winter visit is crank up the heat or get a good blaze going in the woodstove to warm the place up. Then we set about enjoying ourselves – heading outside to play in the snow (and tramping some of it indoors). Cooking, showering, breathing in and out. In other words, loading up the air with moisture.
Then we turn off the heat and leave, and that’s when trouble can start. Cold air can’t hold as much moisture as warm air, so the moisture condenses, especially where it meets cold surfaces. It forms on places like single-pane windows, doors, and even the inside faces of exterior walls. That’s where damage is likely to show up first: water-stained window and door mouldings and mildewy drywall. If this scenario is repeated often enough, it could eventually cause structural damage, rotting out floor sills and the bases of wall studs. Damage to existing insulation is unlikely. In fact, if it’s practical, adding more insulation and a continuous vapour barrier should lessen the problem by moderating the abrupt temperature difference between inside and outside, and preventing moisture from entering the wall cavity.
But if you’re only visiting the cottage a couple of weekends per winter, there’s another way to clear out moisture. Once the heat’s off, and while you’re packing up to leave, open up all the doors and windows. In 20 minutes or so, the air inside should be as dry and cold as the air outside.
In any cottage that’s un-insulated or lightly insulated, cottagers should expect to periodically carry out minor repairs to interior finishes and drywall. Even the sun’s heat will create cycles of warming and cooling that will produce some condensation indoors. The only way to avoid damage completely is to insulate and seal so that you can keep the heat on at a low level year-round.