OTTUMWA — That snow may look light and fluffy, but a few hundred square feet of it sitting on your roof can weigh a ton — or more.
"On average, 6 inches of snow will add 10,000 pounds to your roof load, and this year we are seeing 12 inches to 16 inches," said Anthony Christner, president of Christner Contracting in Ottumwa.
Add some sleet or rain that can soak that foot of snow on a roof, and it's easy to pass the 10-ton mark.
"Newer homes that have engineered trusses instead of traditional rafters ... are designed to handle much of these loads," Christner said. "But in town, we have a lot of older homes built from rafters before there [were] any codes or regulations to follow. Even without the added snow loads, we see a lot of sagging."
This winter, that hasn't been the worst problem.
By the direction they are installed, roofing shingles are meant to shed water, explained Mike O'Hara at O'Hara Hardware. So water coming from above is not typically a problem because rain runs down over the shingles and off the roof. But water coming from below is a different matter.
O'Hara said the problem is when the edge of the roof is blocked; that's when you have the equivalent of a dam around your roof. Water can't run off the roof, so it gets backed up. That forces the water under your shingles, and that water drips into your home or business.
Christner concurred and explained how that happens:
"The number one call we are getting this season is ice damming, and it is up about 50 percent from last year's calls. Ice damming is caused from the heat of the sun and the loss of the heat through the attic melting the snow on our roofs, and in the evening when the sun goes down and temps drop back down the melted snow freezes in gutters and roof edges ... when the snow freezes it expands around and under any shingle that it comes in contact with and forces its way between the sealant on the shingles and allows moisture to penetrate."