We’ve had a mild winter until today! We still have months to go before spring comes, and we’ll no doubt get a few more big snow storms before that happens. There is a certain beauty that comes when you look out and see the world is covered in white, and the way the sunlight glistens through the icicles that hang from trees and rooftops. Though a row of icicles on a house is picturesque, it is also a warning sign… the same conditions that allow icicles to form also make ice dams. As you maintain a comfortable interior temperature for you and your family heat slowly rises into the attic. This heat starts to melt the snow on the roof top, as the snow melt runs down the roof until it eventually reaches the eaves, and this is where ice dams form. The ice forms around the eaves of homes due to a temperature change, the heat that had melted the snow is lost once the roof goes beyond the exterior walls, this slight difference in temperature is all it takes to allow the water to refreeze into a sheet or dam of ice which will melt and refreeze as the days go by. As the snow continues to melt the dam grows in size; the water above backs up behind the ice dam and remains as a liquid. This water finds cracks and openings in the exterior roof covering and flows into your attic space. From the attic it could flow into the home- this may damage exterior walls, insulation and the ceiling finish. It can also lead to the growth of mold and mildew, which could have an adverse impact on you and your family’s health.
To help prevent ice dams the approach is simple, just keep the entire roof as close as possible to the same temperature at the eve. This can be done a variety of ways:
- Ventilation- A ridge vent and soffit vents under the eaves circulates cold air under the entire roof. Both ridge and soffit vents should have the same size openings and between them provide at least 1 square foot of opening for every 300 square feet of attic floor.
- Insulation– Make sure your attic floor is keeping the heat where it belongs, replace damaged insulation and be sure you are hitting the state requirements. Massachusetts requires a minimum R-38 in the ceiling now, but many homes have less insulation. Another newer method of insulation is to have spray foam installed on the roof plane. This is the most effective type of insulation I have found against ice dams. (Each state is different, so be sure to check your local codes)
- Cap, Caulk and Seal- recessed lights, attic hatches, and electrical cables and vent pipes all affect the heat that makes it into the attic space. Recessed lights should be insulated so they will not give off excess heat. Attic hatches/fans should be covered with weather-stripped caps. Lastly check areas where holes have been made for pipes and cables- insulate and seal these areas so that you cannot see light coming in.
- Exhaust to the outside- Make sure that the ducts from the kitchen, bathroom and laundry lead to the outside through the roof or walls. If it goes through the soffit or eave you should rework the exhaust system.
- Moisture barriers- If you are reroofing or installing a new roof put in a moisture barrier (more commonly called an ice and water shield) between the deck and roof covering. This an inexpensive option that will help keep water out of your home due to moisture from ice dams, as well as protecting the house from wind-driven rain if the roof cover blows off during a windstorm.
When the heavy snows come, remove the snow where possible. A roof rake can be used to pull snow down the slope of the roof to prevent an ice dam from growing or forming. Aggressive chipping or breaking the ice dams can cause damage to the roof or gutters. In an emergency situation to stop water from continuing to flow into the house structure, it may be necessary to make channels through the ice dam, so using warm water should be the first attempt. However, the channel becomes ineffective within days, so this is only a temporary solution.
The most important thing to know is that there is no guarantee against ice dams. The best practice is to use a combination of ice and water shield, proper insulation and ventilation- if they are all in good shape, you will have the best chance. If it is too late to have any of these things done, the roof rake is the best prevention. Happy Snow day!