QUESTION: You wrote about roof leaks caused by snow and ice freezing and thawing. I had this problem last winter and was hoping you’d write about how to correct it.ANSWER: Why do roofs leak after heavy snowstorms? Because of ice dams — buildups of ice or snow near eaves or gutters.When heat escaping through the roof melts snow and ice, the resulting water runs to colder, lower areas or eaves, and then refreezes. When the water backs up behind an ice dam, it can find its way under shingles, behind fascias and cornices and eventually inside your house.How do you prevent ice dams?Lower the heat in your house, so less of it escapes and melts the snow/ice on the roof. If you have a flat roof, do the opposite: Raise the heat in the house so more of it escapes, reducing the chance of snowy buildup that could collapse the roof.No one but a professional should climb on a snowy roof. So, how can homeowners clear downspouts?Clear snow around your downspouts from the ground, so that the melting water flows away from your house. Make sure the nearest storm drain on your street is clear.Dislodge ice in the downspouts by hitting them with a hand, then remove the ice from the spout. If the ice can’t be forced, carefully pour boiling water on it.If your roof has a tendency to develop these dams, you might need professional advice on how to prevent them.One way is by installing underlayment on the roof — obviously under the shingles. W.R. Grace, DuPont, and a number of other manufacturers make this product.