When temperatures plummet and snow starts falling, many of us reach for the shovel or snowblower. Smart homeowners, though, remember to look up too — and check their roofs for ice. Ice dams are accumulations of ice on the edge of the roof — and they mean Big Trouble for you and your home, so be on the lookout.
What’s the big deal, you ask? Ice dams result in water seepage, which can rot roofs, destroy insulation, flood attics and ruin gutters. Moisture damage can extend far inside the home, damaging ceilings, paintwork and belongings. The dampness encourages mold, too, which can trigger nasty allergies.
You may have heard that gutters cause ice dams by providing a place for water to collect. Wrong! You may also have heard that installing heating cables along the gutter line is the best way to prevent ice dams. Wrong again! Yep, there’s a lot of misinformation out there. Let’s look at where ice dams really come from.
How Ice Dams are Born
In poorly insulated homes, warm air escapes through the ceiling and into the attic. If ventilation inside the attic is also inadequate, all that warm air has nowhere to go. Result: the roof’s temperature starts to creep up higher than the outdoors air temperature, causing accumulated snow on the roof to begin melting.
Water then trickles down the slope of the roof until it once again hits a cold patch, usually the gutter. There it refreezes, gradually forming a dam that prevents runoff. Additional melting snow, having nowhere to go, starts seeping inside the house — and that’s where the homeowner’s headaches begin.
A Cool Solution: Insulation and Ventilation
The only way to permanently eradicate ice dams is not to warm your roof up (with heating cables) but to cool it down with better insulation and attic ventilation. Until then, you’ll go right on experiencing ice dams in severe weather. Any other strategy will provide a temporary fix, at best.
In northern states, attic insulation should be at least 12 inches deep. Make sure it is installed correctly, without any gaps between sections, and in conjunction with a vapor barrier. While you’re at it, check that attic heating ducts are located as far as possible from the roof.
Also check around light fixtures, chimneys, bathroom fans and anywhere else heat might escape upwards. If you discover small holes, seal them up with caulk, spray foam or weather-stripping.
Next, evaluate your attic’s ventilation system. Are there adequate inlet and outlet vents? If not, look into installing a continuous soffit and ridge ventilation system. Here’s how it works: a vent is installed that runs the entire length of the roof at its apex.
We all know hot air rises, right? In this case, the hot air now has somewhere to go, naturally flowing up and out through this new attic vent.
Meanwhile, that draught of air upwards and outwards creates a vacuum, sucking cold outdoors air into the attic via soffit vents, further cooling down your trouble zone. The beauty part is there are no fans or wires or anything else to be maintained. Nature does all the work for you!
Help! There’s An Ice Dam on My Roof.
Your best strategy is to sit tight and wait for the ice to melt away. Later you should focus on preventing future dams by making the improvements described above.
Before you decide to manually chip away at an ice dam, know that it’s not recommended, and best left to a professional. For one thing, you could seriously injure yourself. (Never, ever climb up on an icy roof. If you must inspect the ice dam up close, use a ladder and beware of falling debris.) Second, forcibly dislodging chunks of ice could easily damage your roof and gutters, worsening your leakage problem.
If you really, really can’t stand just waiting it out, here’s an ice-melting tip courtesy of This Old House: Cut the legs off a pair of pantyhose, fill with calcium chloride ice melter and lie them down the slope of the roof so that each leg crosses a section of ice and the toes dangle over the edge of the gutter. This should melt small channels in the ice, allowing runoff to occur.
Icicles hanging along the eaves of your house may look beautiful, but they spell trouble. That’s because the same conditions that allow icicles to form—snow-covered roofs and freezing weather—also lead to ice dams: thick ridges of solid ice that build up along the eaves. Dams can tear off gutters, loosen shingles, and cause water to back up and pour into your house. When that happens, the results aren’t pretty: peeling paint, warped floors, stained and sagging ceilings. Not to mention soggy insulation in the attic, which loses R-value and becomes a magnet for mold and mildew.
Birth of an Ice Dam
1. Heat collects in the attic and warms the roof, except at the eaves.
2. Snow melts on the warm roof and then freezes on the cold eaves.
3. Ice accumulates along the eaves, forming a dam. Meltwater from the warm roof backs up behind it, flows under the shingles, and into the house.
Hacking away at ice dams with a hammer, chisel, or shovel is bad for your roofing—and dangerous for you. And throwing salt on them will do more to harm to your plantings than to the ice. Short of praying for warm weather, here are two stop-gap measures we recommend:
•Blow in cold air: Take a box fan into the attic and aim it at the underside of the roof where water is actively leaking in. This targeted dose of cold air will freeze the water in its tracks. “You’ll stop the leak in a matter of minutes,”says TOH general contractor Tom Silva.
•Rake it: Pull off snow with a long-handled aluminum roof rake (above) while you stand safely on the ground. A rake with wheels won’t harm the roofing.