Winter means snow, and where there’s snow, and where there are roofs, there are plenty of opportunities for maintenance problems. Winter and spring-thaw leaks are a major pain, and they can happen to shingle roofs that handle rain just fine. Here are some pointers on how and where problems start, and what to do about them.
Low-slope roofs are the leading culprits because they can build up a decent pile of snow, and when it starts to melt, it doesn’t take much to build up an ice dam along the eaves, where the roof deck is cold and the trickling flow refreezes. The dam causes meltwater to pool behind it. With nowhere else to go, the water finds its way down through shingle nails. You can tell if you have a dam forming (and if you have a melting issue) by the amount of icicles that forms along the drip edge or descends from the gutter.
To get melting happening in the first place, you need heat. Problem-causing heat comes from below, from inside the building, because of poor insulation in a cathedral ceiling or an attic space. But heat loss in and of itself isn’t necessarily the problem: it’s poor ventilation, which doesn’t allow the warm air beneath the roof deck to escape. “Ice dams on roofs are typically caused by either lack of insulation or lack of ventilation,” says Roger Frost, a leading home inspector in Barrie, Ontario, with plenty of experience with structures in winter. “Ideally the temperature inside the attic should be the same as the exterior temperature, but in reality this never happens.”
“Some home builders add things like skylights and fancy dormers, and they end up accidentally creating heat spots, places where air gets trapped,” says Mike Vettesse, owner of GBS Contracting Services, a Gravenhurst, Ontario-based roofer with an A+ Better Business Bureau rating. “As long as there is a slow, even flow of air in an attic space, it will be ok.” Roger Frost uses thermal imaging to show clients where problem areas are, and he stresses the importance of proper soffit vents or baffles. “These products ensure that adequate exterior air is directed into the attic. The Ontario Building Code requires at least 25% of attic ventilation is supplied via soffit vents.”
If you have a cathedral ceiling and a chronic problem with ice dams, the solution may be to build a roof on the roof. A contractor will use two-by-fours or two-by-sixes, set on edge on the existing roof, to create a new roof deck. The additional space can be properly ventilated, from the soffit to the roofline. Another strategy is to install the sort of heavy membrane used on flat roofs beneath the the shingles. With a problem roof, a typical membrane is not going to be able to withstand leakage caused by dams.
If you’re not using your cottage in the winter, the risk of leaking should be minimal, because you’re not heating the building to a comfortable level for occupancy. Similarly, screened porch roofs are at much lower risk of winter leaks because they are going to be equally cold, above and below the roof deck.
The surest (and pretty much only) low-tech way to avoid leaks with a roof plagued by heat loss and poor ventilation is to keep the snow off it, by shovelling, or at the least by using a roof rake to clear the roof several feet back from the eaves, where ice dams tend to form. Snow exacerbates the problem because it’s a good insulator, trapping heat below it on the roof deck, where melting happens.
Shovelling is not for the faint hearted and can lead to serious injury in a fall. If snow loading on a problematic roof is an issue, consider contracting a roofer or property maintenance company to do it for you. Make sure they carry liability insurance in case one of their own workers falls.
Heated cables are sometimes used to control or eliminate ice buildup along the roof edge and in channels and gutters. But if they’re not installed or used properly, they can cause more problems than they solve, by creating the melting that causes the problem in the first place. Some store-bought cable systems come with sensors that will automatically turn them on and off, depending on the temperature of meltwater in the gutter (if there is one). Vettesse advises that store-bought DIY cables might last you two to fives years, tops. He recommends a commercial cable system, professionally installed, made by Heat-Line Corp, in Algonquin Highlands, Ontario. Its sensors will only apply heat when necessary, and the system comes with a 25-year guarantee.