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Handyman on call

Wintertime worries

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By Peter Hotton
Globe Staff / February 3, 2011

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My chat room was inundated by questions on ice dams, frozen gutters, snow or ice on the roof, and other plagues of winter. So today’s question is not a question at all, rather a treatise on the indignities foisted on innocent homeowners.

Ice damns

They are called ice dams. I prefer ice damns. It is appropriate, considering the damage done by ice dams on otherwise sound houses. For clarity sake, we will stick with “dam.’’ There is a single cause for ice dams and leaks there from: A warm roof. Not gutters or the lack thereof, not frozen gutters, not low-pitched roofs.

What happens is this: Snow builds up on the roof and tends to melt from the bottom up, but a cold snap freezes the water, making the dam. Then more snow melts above the dam but is stopped by the dam, and backs up under shingles, leaking into the attic and often into houses, usually close to an outer wall. Gutters? They simply freeze up and fill with ice, causing water to flow over them. In a house without gutters, water flowing over the roof edge will form icicles, often huge ones.

The cure: The roof must be made colder. To do that, install insulation or more insulation in the attic floor, and keep it out of the eaves and soffit vents. Ventilate the attic: Install a ridge vent along the entire length of the roof’s ridge. Install soffit vents on the soffit, which is the under part of the roof overhang. The best soffit vent is a continuous 2-inch-wide screened strip, going the full length of the soffit, on each side of the house. Those little round vents, even big ones, spaced along the soffit, are useless. With a cold roof, there will be less bottom melting and refreezing of the water; no ice dams.

Another way to insulate the attic is with a new technique of insulating the attic ceiling and all walls, but not the floor, with Icynene, an excellent foam insulation, and closing or removing all vents. It goes against traditional insulating methods, but it works. It is very expensive but is permanent, and will do the job. There is yet another fix, but it will not prevent ice dams, only leaks from them. And that is a covering of an ice and water shield, a rubbery membrane that prevents dammed water from getting under shingles and leaking into attic/house. This shield is installed under shingles, so it is best done when the house is reroofed. At first, roofers put in a 3-foot-high strip along the edge of the roof. They found that ice dams can occur above this 3-foot-high strip, so they recommended a 6-foot-high strip. Now they often recommend 12-foot-high strips, or the entire roof.

Icicles, small and humongous

When gutters fill with water and freeze, they cause the ice to build up and roll over the edge. In a house with a cold roof, icicles are less than a few inches long and are harmless. With a warm roof, more water cascades, forming humongous icicles, 4 to 5 feet long with tree-trunk diameters.

Those big ones are dangerous, and often are very hard to break off.

A cold roof will help. But nothing else can be done now except to fence off the area and have a professional cut them out. Because large icicles hang from gutters, they can pull down gutters with them, so cutting them out is important.

A fix for frozen gutters is to install heating cables in the gutters and downspouts to keep them working. Turn them on as the need arises. Turn them off as long as the gutters are collecting and draining water. Such heating cables are unlikely to warm a roof.

Removing snow from a roof or deck

In most cases, removing snow from a roof or deck is not necessary. New England homes and most in the snow belt and northern third of the country are sloped and can easily bear up against snow, ice, and water weight. The same goes for snow on decks. A flat roof, especially one with a parapet on all sides that tends to keep snow from going over the edge, is another story. Generally, the snow should be taken off such a roof.

Globe Handyman on Call also appears in the Sunday Real Estate section. He is available 1-6 p.m. Tuesdays to answer questions. Call 617-929-2930. Hotton (photton@globe.com) also chats online about house matters 2-3 p.m. Thursdays. Go to www.boston.com