These days, new homes with woodstoves rarely get a new brick chimney. Instead, most builders specify a stainless-steel chimney, which is less expensive and faster to install than a brick chimney.
Typically, a woodstove requires a UL-listed double-wall or triple-wall chimney called a Class A chimney pipe. Manufacturers of this type of chimney sell lots of accessories, including roof penetration kits and roof flashing kits to allow for a weathertight installation through a roof. What does such an installation look like? Here are examples of typical installations:
What the metal chimney manufacturers don’t tell you is that chimneys installed this way may not long last long in a snowy climate.
Beware of roof glaciers
Deep snow on a steep roof acts like a glacier. Affected by gravity, such a glacier moves downhill, either gradually or suddenly, depending on the roof slope and outdoor temperature. When the glacier encounters a metal chimney, it can push the chimney out of plumb or tear the chimney off the roof.
This problem is more common in snowy climates than mild climates; more common on steep roofs than shallow-pitched roofs; and more common on metal roofs than asphalt shingle roofs.
What are the possible solutions? One solution is to install a snow guard uphill of the chimney. (For more information on this approach, see “Snow Guards for Vent Pipes.”)
A curb for your metal chimney
Another possible solution was recently suggested by GBA reader Malcolm Taylor, a builder in British Columbia. After architect Bob Swinburne noted in a GBA comment, “I always worry about snow taking out the chimney,” Malcom wrote, “Taking cues from Ted Benson’s…
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