This time of year, when roofs are covered in snow, some people are practicing a decades long tradition of using a roof rake to remove even small amounts of snow. That’s a horrible idea. In most cases all you are doing is scraping off a protective layer of shingle granules.
There are exceptions to this rule.
1) If you have multiple layers of shingles on your roof.
2) There is a heavier than normal snow load on your roof AND a low slope roof where snow may not blow off of your roof as is normal in nearly all other roofs.
3) Your roof is not ventilated so ice collects at the gutters edge and damage ensues from ice damming. This is common in houses that do not have soffits to allow intake air for ventilation.
But most people don’t fall into those categories.
Most people are simply damaging their roof and causing additional work for themselves. And why?
Because they are misinformed.
I have replaced roofs with as many as 5 layers of shingles on them. Yes, it is illegal to put that many layers on a roof but some less than scrupulous contractors have offered to save customers money by skipping the tear offs. When you combine that large amount of weight with snow loads, you can have a collapse. But there is one distinct difference between now and 20 years ago.
There is another exception to the rule. Some houses, especially cape cod style houses, do not have soffits (the underside of an overhang). This means that it is virtually impossible to properly ventilate your roof. While there are some products that can allow intake air flow (fascia flow comes to mind), they are cumbersome to work with and require additional work on your fascia, gutters and in order to accommodate the additional depth of the product, an unsightly extension of your shingles on the bottom side. If you are having your roof installed in the near future, you can avoid this problem by including fascia-flow as part of your product.
Aside from the exceptions I have listed above, you want to avoid roof raking.
Most scrupulous contractors today will only agree to do a roof if they do a total tear off of the old shingles. This process removes what can be inches of asphalt, and its accompanying weight, from the structure of a home. If your roof has been properly replaced there is none of that unnecessary weight Structurally, buildings are made to bear the weight of snow.
So unless your home has the three key risk factors (noted above) that could lead to structural failure, give your shingles a break. Otherwise, you are reducing the life of your shingles.
Jim McGuigan is a ventilation certified, GAF Certified Roofing Contractor living in Brown Deer and serving Southeastern Wisconsin.