How to prevent ice dams from damaging your roof

What is an ice dam?

An ice dam is exactly what it sounds like – a block of solid ice stopping water from flowing off your roof. Icicles forming around the edge of your roof are a sure sign that the condition of your roof is ripe for ice dams.

On most homes, if ice dams are forming, you can clearly see them – large chunks of ice forming around the edge of the roof where the temperature is the coolest. If you see ice dams forming, time is of the essence. It’s only a matter of time before meltwater pools up behind the ice dams, gets under the shingles, and into the house.

Ice dams are a common winter roofing problem for homeowners in cold weather climates like Chicago and if left untreated, ice dams can cause expensive damage to your roof, gutters, drywall and can even cause mold.

What causes ice dams?

First things first, ice damming is not a roof covering problem but an attic ventilation and insulation issue. It’s important to understand that shingle roof covering is a water shedding system, not water proving.

Here’s how it works:

When that heat warms up your roof, the snow on top of it starts melting and freezing. Ice starts to build up, especially along the unheated roof edge, and blocks roof surface drainage, which causes water to pool upwards, and possibly leak beneath the structure. The longer you leave it, the bigger the dam will grow.

In a perfect world, the temperature in the attic during the winter months should be the same as the outside. Realistically, this can only be achieved on unheated structures like detached garages. For any heated structure some loss of heat raising to the attic and the roof is unavoidable even with best air sealing and insulation. That’s where proper roof ventilation is absolutely necessary to solve the problem.

Image courtesy of the University of Minnesota. Image source:https://extension.umn.edu/protecting-home-rain-and-ice/dealing-and-preventing-ice-dams

Conditions are ripe for ice dams if the following three things happen:

1. There is a significant amount of snow on the roof.
2. The outside temperature is below 32 degrees.
3. The high part of the roof is above 32 degrees and the low part is below 32 degrees.

Top Three Prevention Tips

1. Keep the attic cold

To prevent ice dams from forming in the first place, you have to stop excess heat from getting out of the house through your attic.

Ask yourself this: how insulated is your attic space?

In most homes, heat loss by air leakage through the attic is the major cause of heat transfer to the roof. Insulation is often overlooked in this part of the house and there is little space for it.

Insulation

The best prevention for ice damming is to seal all attic air leaks and insulate. Proper insulation will keep warm air from escaping the lower levels of your home into the attic space.

In a lot of homes, this is easier said than done. Many attics, including those under low-sloped roofs, don’t have a lot of room for adequate insulation.

In this video, learn how to insulate an attic to prevent ice dams from ever coming back.

Ventilation

Ventilation is another important part of any roofing system.

Attic warming from poor ventilation can be made worse if there’s heat from lighting or a chimney coming from the floor below. A good ventilation system in the attic will help prevent temperature fluctuations, keeping the air in the attic cool and the roof deck cold.

This video explains the importance of proper ventilation to your roof.

2. Rake the roof after a heavy snow

Roofs, like the rest of homes, are designed to withstand heavy snow. Still, it’s a good idea to scrape snow from the roof after a heavy snowfall if you live in a single story home and can do so safely.

Use a long-handled aluminum roof rake – available at most home stores – while you stand closely on the ground.

In this video, see how it looks to safely remove snow from a rooftop.

3. Keep your gutters clear.

Around November, before winter comes, have your gutters cleaned and make sure the downspouts are working properly. If your gutters are clogged, melted snow can’t go anywhere and ice dams will form quickly after the first big snowfall of the season.