By Eric Mazden
Gone is the season of comfortable fall strolls and pumpkin spice lattes, and in is the season of blizzards, icy roads, and of course, ice damming. You may be familiar with this term if you are a home owner living in a colder climate such as Canada or the northern United States, or you may be one of the lucky ones who have never experienced it at all. This blog is intended to inform home owners of the potential for ice damming and the negative affects it can have on your roof. I will also discuss some ways to prevent ice damming from occurring in the first place, and methods you can use to prevent further damage from your roof system if you have already experienced ice damming.
Ice dams form when the heat escaping your home warms the roof sheathing and underside of the snow layer. As the snow melts this water trickles down the slope of the roof and freezes on the cold roof surface over the eaves, creating a “dam” of ice. This dam of ice allows water to pool over the warm roof surface, which will eventually lead to degradation of your shingles and a leaky roof. Now I’m sure you are wondering why this heat is escaping in the first place, but there are a combination of factors to blame.
A good air-vapour barrier is the best defence against air leakage. All homes should be equipped with a continuous air-vapour barrier on the warm side of the insulation. This will prevent warm-moist air from escaping into the wall or roof assembly, and keeping the air-vapour barrier warm will prevent any air already in the cavity from condensing on its cold surface, resulting in damaged insulation, etc.
Needless to say, the less insulation you have, the more heat loss you will experience. A well-insulated house will not only aid in retaining the heat, it will also help to retain cool air in the warm part of the year. Insulating a roof properly while achieving the required amount of ventilation can be tricky, especially in sloped (cathedral) ceilings. In this case, spray foam insulation is often used as a way to insulate the underside of the roof sheathing, which eliminates any air space that would require ventilation. Spray foam also has the characteristics of an air-vapour barrier, which means that you will not require one at the ceiling level. This is a great solution for cathedral ceilings because you don’t have to worry about trying to keep loose insulation or batts from sliding down the slope of the ceiling over time, resulting in poorly insulated areas.
Any gap that is left between the top of the insulation layer and the underside of the roof sheathing must be properly ventilated. Ventilation is important to ensure that any warm-moist air that does escape into the attic space, has somewhere to go, and is replaced with cool-dry air. In a house with a typical sloped roof and flat ceiling roof vents, gable end vents and soffit vents are relatively easy to install and together will typically provide enough ventilation. Problem areas typically occur close to the eaves where it can be challenging to install the proper level of insulation, while still allowing an air space to the soffit vent. Often times your roof truss supplier can design a higher heel height into your truss to allow for more insulation closer to the eaves without impeding on the vent space.
While these are the three main factors that can lead to ice dams forming, there are some other methods to help prevent them from causing damage to your roof. Eave protection is a roof underlayment that limits the damage caused by the pooling of water caused by ice damming. This is typically a self-adhering, waterproof product that is installed from the edge of the eave up passed the plain of the exterior wall. If you have experienced the negative effects of ice damming, this product can be installed the next time your roof finish needs replacing.
In summary, ice dams have proven to be a frustrating, but realistic part of living in colder climates. It is crucial to get an understanding of the science behind why and how they occur in order to come up with ways to prevent them or limit the damage they can cause. Take the time to inspect your roof this winter to see if there is evidence of ice damming, and use some of this knowledge to help save your roof!