Guide: Repairing the cottage roof
Weather conditions can do a number on the cottage roof. Here's how to make it watertight
On a metal roof, you’re looking for corrosion — possibly on the panels themselves, but more likely where two different metals might touch: around fasteners and flashings, chimneys, valleys, dormers, plumbing stacks, guy wires, and vents. You might find panels loosened by ice and wind, but you’re more likely to see gaps at the flashings, etc., where “tarred-together” seams have separated.
With asphalt shingles, look for cupped tabs, torn shingles, curled edges, and surface wear as well as the usual suspects: flashing, chimneys, valleys, and so on. Surface wear shows up as bare patches, where the granular coating has come off. The first hint of such aging might be a sediment of little stones in the gutter several years after installation. These are supposed to cover the shingle completely, protecting it from the sun. Sliding ice and snow can wear it off, as can too much foot traffic. Once the aggregate is off, the asphalt begins to break down even more rapidly and, when that cracks, there’s little left but the base material. The most common base is an organic felt — or mat — of wood fibre and recycled paper. The base without its granules and asphalt may be little more than a pulp of old telephone books.
Oddly enough, water is the other natural aging factor for asphalt shingles. Water absorbed by a shingle, starts to break it down, especially during freeze-thaw cycles. Moss and algae on the roof accelerate aging, not directly but by trapping moisture against the shingles. Then there’s the weight factor. By some estimates, an old organic shingle can almost triple its weight with water retention – something to think about if you’re wondering whether your roof can hold another layer of shingles atop the old.
Cedar shakes and shingles suffer some of the same weathering effects as asphalt. Cedar is naturally rot resistant, but wet-dry cycles lead to checking. Water, caught in the cracks or under moss, expands when it freezes and accelerates the deterioration. The good news is that the aging effect of sunlight on cedar — turning it grey — doesn’t have the same destructive effect as it has on asphalt.
This article was originally published on November 4, 2003