Prevent Ice Dams from Forming on Your Roof

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. Now What?
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.

See also:
Fast Fixes for Ice Dams
How to Fix a Broken Gutter in a Storm