By virtue of being involved with roofing industry, I am often asked how to stop ice dams from forming on the roof. So, rather than answering individual questions, I decided to write this helpful guide for homeowners who are looking for simple ways to prevent ice dams.

Before we begin, let’s define an ice dam, and examine how an ice dam forms. An ice dam, is literally a wall of ice that forms on the outside edges / eaves of a sloped roof, and in the gutter. The wall of ice prevents the water formed by means of melting snow to properly run down, which causes it to run down the walls of the building damaging ceilings, wetting insulation and causing rotting and damage to walls and paint.

What cause an ice dam, and how does an ice dam form? The mechanism of an ice dam formation is best explained by poor insulation, and ventilation of the building’s attic. When the attic is poorly insulated, the warm air from inside the building escapes through the attic and rises up to the pick of the roof, where it warms up the roofing surface, which melts the snow seating on the roof. The snow begins to melt and melted water runs down the roof slope, underneath the blanket of snow. When it reaches the eave of the roof, it begins to refreeze again forming a wall of ice, which turns into an ice dam.

As you can see in the picture above, the upper portion of the roof is exposed as the snow has melted, and water ran down, and turned into an ice dam, that looks rather extreme! The reason, for the exposed roof shingle, is that warm water that was rising up in the attic, reached the highest point in the attic where it transferred the warmth to asphalt shingle, which in terms has melted the snow on top of the roof. When the melted water reached the edge of the roof, which was not as warm as the top, the water refroze forming icicles  and ice dams on the roof. As you can see, the mechanism of ice dam formation is not external, but rather internal, and has to do with inadequate insulation in the attic.

How to prevent ice dams? Clearly an adequate insulation is the key in preventing ice dams from forming in the first place. As long as, we can find a way to keep the warm air inside the house, and stop it from leaking into the attic, we can stop the ice dams from happening. Thus, we have to find a way to properly and fully insulate our attic.

Attic Insulation

For most roofs located in areas with snowfall a minimum of R – 49 insulation value will be required. If your home is 30 years or older, than chances are that it is not properly insulated, and you will improve the energy efficiency and functioning of your home by upgrading your insulation to R -49 value. So if you have an older home, you will first want to find out how much insulation you already have. An easy way to measure your attic floor insulation is by measuring its thickness, which you can measure with a simple ruler, and then multiply the thickness in inches by 3.14. This will give you the approximate R-value. Thus, if you have six inches of Fiberglass blanket insulation, you will get; 6 x 3.14 = 18.84. which means that you need to get an additional 10 inches of attic floor insulation for your home to meet the Department of Energy Requirements.

Refer to to Energy Star’s recommended levels of insulation table to determine the proper R – value for your geographic zone.

A word of caution:

If your home is a victim of ice dam formation, and you consider adding additional insulation to your attic, stop right here, and check for air leaks and drafts in the attic, ceilings and in between the walls before you add more insulation. Properly sealing the leaks in your attic, will play a major role in helping you prevent the ice dams. Take time to identify and locate air leaks in your attic and seal them with caulk, spray foam, or weather stripping. This will make your attic more energy efficient, and you should not add more attic insulation until you have completed this step first.

Attic Ventilation

Once your attic is properly sealed and insulated, it is time to examine attic ventilation. Ideally, you will have sufficient soffit vents, which will allow for air circulation aimed to remove warm air from the attic and bring the cold air from outside. Remember, as long as we can keep our attics, cool, we can prevent warm air from rising up and warming up asphalt shingle, which melts the ice and causes water to run down the slope underneath the snow pack. A home energy contractor can advise on appropriateness of your attic ventilation and recommend adding additional ventilation measures to your home.

When buying insulation materials, be sure to choose energy star rated products, which by the way, qualify for energy efficient improvements and can earn you governmental tax credits. Also, consider insulating walls, and and windows in your home, which will further increase energy efficiency of your home. Doing so, will help keep your home cooler in the summer, warmer in the winter, and prevent the ice dam build up.

As one of the best methods to deal with ice dams problem here in the snow country is to use standing seam metal roofs. This will be especially useful if other methods cannot be used for various reasons or are ineffective. Standing seam roof will let the snow simply slide off the roof, and ice dams won’t be able to form. Even if ice dams do form, for example if there is a snow retention system in place, the single-piece standing seam panels will not be vulnerable to the water back-ups as is the case with asphalt shingles.

Check out how standing seam metal roof is installed:

Please share your successful attempts in preventing ice dams, and ask more questions if you have them.