How to Prevent Ice Dams on the Roof

Winter season brings us heavy snowstorms, low temperatures, and ice dams. Are you one of the many homeowners who have to worry about the unsightly ice dams and icicles hanging down from the eaves of the roof and causing damage to the roof, gutters, and your home this winter?

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Why Ice Dams are Dangerous

The major issue with ice dams on the roof, is that they trap the melting water running down from the top of the roof, and thereby cause it (the melted water) to rise up underneath the roofing shingles, and eventually seep through the boards and walls inside our homes.

ice-dam-formation

What causes Ice Dams?

The heat from inside the house rises up into the attic space where it continues to rise reaching the apex of the roof. The warm air warms up the top of the roof, which causes the snow accumulated on top of the roof to melt. The melted snow turns into water that starts running down the roof surface underneath the snow-pack. When the water reaches the colder edges at the bottom of the roof, it refreezes forming a wall of ice. This wall of ice is commonly referred to as an ice dam, because it traps the melting water like a dam.

Common Misconceptions:

Although, ice dams can sometimes reach the gutters, they do not form in the gutters, but rather they form at the eaves of the roof. If you can get your attic-space air temperature to stay at 30° F, or lower (during heavy snow fall accompanied by low temperatures), then you should be able to eliminate ice dams from happening in the first place.

Prevention:

First and foremost, your roof needs to have at least 2 feet of ice and water installed at the eaves and valleys of the roof. The ice and water should be installed underneath, and prior to the installation of roofing shingles (weather metal or asphalt) on your roof. The rest of the roof should be covered with a roofing felt also known as roofing underlayment. Finally, roofing shingles upon your roof need to be properly installed.

Solving the root cause:

One of the easiest long-term solutions to prevent ice dams is to minimize the impact of the warm air that contributes to ice dam formation on your roof. One effective way to stop the warm air from escaping into the attic is to use a proper insulation on the attic floor. You will find that most older homes do not have sufficient levels of attic insulation. To further complicate this problem, many homes with the insufficient attic insulation also have many air leaks and subsequent home-to-attic warm air drafts that literally drive the warm air inside the attic.

Step 1. Sealing air leaks leading into the attic space

Locating and properly insulating all the little pathways through which warm air rises up inside the attic is critical for an effective long-term solution to ice dam problem. You will want to properly identify and seal these holes. Use the weather stripping to properly insulate and seal all the little holes through which the warm air escapes into the attic.

Step 2. Insulating Your Attic Space

The next step is to bring up your level of the attic floor insulation to a level specified by Energy Star. You will find that for the majority of homes within the snow belt zone, the required level of attic insulation should be equivalent to R – 49 value. Once again, most older homes are not properly insulated, which means that you will have add additional attic floor insulation to your home’s attic. Before you can add additional insulation to your attic, you will have to find out the current level of insulation in your attic.

  • Grab a simple ruler, and measure the height of your attic floor insulation. Then, multiply the height in inches by 3.14. This will give you your attic floor’s current insulation R – value.
  • If the level of insulation in your attic is not sufficient, then head out to your local home improvement center and purchase additional levels of energy efficient attic floor insulation pads.

Step 3. Lay out additional attic floor insulation pads

Do not lay, nor push the attic floor insulation into the corner where attic floor and roof walls meet, because it will create a cold area at the edge of the roof, which could contribute to the ice dam formation. Further, you do not want to block the air in-flow through the soffit vents located at the edges of the roof.

Step 4. Ensuring sufficient ventilation of your attic space

Once your attic is properly sealed and insulated, it is time to ensure that your attic is also properly ventilated. First, check to see if your roof has the soffit vents installed. If that is the case, then you’re in great shape, because soffit vents are designed to drive cold air inside your attic. If not, then you need to have gable vents installed as an alternative to soffit vents. Sometimes you can get away with installing roof vents in lieu of gable vents. The rule of thumb is to have one square foot of gable ventilation, or roof ventilation, for every 150 square feet of the attic floor. If there are soffit vents, then there should also be a ridge vent installed on your roof.

If there is a gas furnace installed in your attic, then you will need to make sure that it is professionally insulated, and you will also want to have a power ventilation professionally installed in order to help cool off your attic.

Once you have attained an adequate level of insulation and ventilation in your attic, your roof should be in good shape for a major snowstorm and the onset of low temperatures. If you need a short term solution for dealing with ice dams that have already formed upon your roof, then consider the tools and alternatives outlined below:

Ice dam prevention products:

Heating cables

Heating cables can be installed at the eaves of your roof, and turned on during and after a snowstorm to help melt the snow at the edges of your roof, which should help you stop the ice dams. You will have to remember to turn your ice melting cables on and for it to work. You will also have to remember to turn them off before they burn out! Finally, you need to make sure that your heating cables are properly grounded during the installation.

Snow Rakes

You can use the snow rakes to push up and clean up the snow on your roof, which should help you stop the ice dams from forming.

Keep in mind that heating cables and snow rakes are just temporary measures, and at some point, you will probably want to have your attic space adequately insulated and ventilated as part of your long-term ice dam prevention and heat loss strategy.

Metal Roofing

Another option to consider is a metal roof. By installing a metal roof that has a special coating designed to shed snow and ice causing it to fall off the roof before it has a chance to form into an ice dam, you can completely eliminate ice dam formations on your roof in the first place! You will still want to have an adequate level of insulation installed in order to prevent a heat loss from your house. Keep in mind that a metal roof will not cause a loss of heat in the winter, but an improperly insulated attic space will.

Finally, installing an energy efficient metal roof, can help pay for itself over a long run, because a metal roof can last three times longer than an asphalt shingle roof, and it can also help you save about 30% on your cooling costs in the summer. Thus, a metal roof can eventually pay for itself through its longevity and superior energy efficiency.

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3 comments

  1. Currently, I have an asphalt shingle roof, and every winter I have to deal with some serious ice dam issues, where ice sticks to the shingles at the eves and If I try to remove it with a snow rake, it rips off small pieces of shingles as well as sand granules.

    I live in Manchester, New Hampshire and whenever I venture north, I always see sheet metal roofs in our neighboring states of Maine and Vermont. Now, granted there is a lot of snow fall in this part of northern New England, and I was wondering if this is the reason why I see all these metal roofs around here?

    Will a metal roof actually help to protect my home from all the snow and ice dams? Is it more effective than shingles for stopping ice dams? And finally, what is the best type of metal roof for northern region?

    1. Hello Michael,

      Glad to hear from a fellow New Englander!

      Since ice dams on a roof typically form whenever there is heat or warm air escaping from your home into the attic space thereby causing snow at the apex of the roof to melt, and refreeze at the eaves, as melted water reaches the colder edges of your roof. Thus, you will want to address the fundamental insulation and ventilation issues; improving your attic floor’s insulation, with eliminating any drafts where heat or warm air may be escaping from the house, and ensuring that there is sufficient ventilation of your attic space to vent out any warm air in order to keep your attic space cold.

      As far as the best choice of a metal roof, I would recommend any metal roof with a sleek surface designed to shed snow and ice. I would also recommend that you get a batten system to form the air pocket between a metal roof and your roof deck. Alternatively, you can install a metal roof over the layer of appropriate insulation. You will find that many standing seam and exposed fastener metal roofing systems are designed to work with a batten system.

      With metal shingles, you will need a solid surface such as plywood, therefore you will want to remove your existing roof, install battens to form the air pocket, and then install plywood sheets over battens provided that your roof structure can support the weight. Alternatively, you can install a metal shingles roof over the existing shingles (if there is only have one layer of shingles on your roof).

      As long as your attic space is properly insulated and ventilated, you should be in good shape with most any metal roof. Good Luck!

  2. I have a gas furnace in attic in new England. we had spray foam insulation put on rafters and vents to make a closed sealed attic space to help prevent ice damming. We had a new shingle roof installed 5 yrs ago with 3 feet of ice damming product. we had leaking into the house. I want to put exposed fastener metal roofing on top of shingles with ferring strips to prevent ice damming. My wife wants to remove old shingles and put ice damming product all the way up the roof and then re-shingle. this is only going to be on north side of roof. What do you think is the best option? the attic temp is a constant 70 degrees in winter.

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