Photo by State Farm, acquired via Flickr.com
Dealing with Roof Damage from Ice Damming
You've probably seen or heard of ice damming, but you may not know how it happens or how to fix it.
How Ice Damming Happens
It starts in the attic. In winter, almost all homes lose heat into the attic, making the attic warmer than the outside.
If there is snow on the roof, the underside of the snow will begin to melt because of the warmth. Water will then trickle down your roof underneath the snow.
Once the water reaches the overhang and the eaves trough, which are colder than the part of the roof above the attic, it re-freezes.
If the right conditions persist, the ice fills the eaves trough and begins to accumulate on the roof. At this point, the trickling water can no longer flow into the eaves trough. Instead, it backs up under the shingles and will start to penetrate the plywood sheathing of the roof.
The ice build-up and water penetration can damage your eaves troughs and roof, but even more damage can occur if the ice damming continues.
Once the water has penetrated the sheathing and entered the attic, it begins to flow down toward the ground.
Most times, the water drips down outside the outer wall, and no damage is done to the inside.
However, if conditions are right (like they were for many people this winter), the water will drip down inside the walls. This can cause water stains on inside walls and water leaking through the ceiling.
One-Time Ice Damming
For many homes, ice damming is a very rare occurrence.
It's not necessary to replace your entire roof just because of one episode of ice damming during a particularly bad winter. Instead, simply repair the inside damage.
The next time your shingles are due for their regular replacement, ask your roofer to lay a strip of ice shield under the shingles.
This is a flexible plastic membrane that is watertight and extends at least three feet up the slope of the roof. This membrane prevents water from penetrating your roof if ice damming happens again.
Recurring Ice Damming
When ice damming happens every winter, you will need to take additional action to fix the problem.
First, check your eaves troughs for blockage. Eaves troughs accumulate leaves and other debris, and must be cleaned regularly. Blocked eaves troughs make it much easier for ice damming to occur.
Second, pay a visit to your attic. Here, a combination of proper insulation and ventilation is necessary to prevent a temperature difference from building up between the attic and the outside.
Your attic should be insulated to R50. Proper ventilation is most important if your attic is underinsulated, but can sometimes still be a factor even if you have enough insulation.
(The Ontario building code calls for 1 square foot of ventilation per 300 square feet of attic floor, but this is a benchmark, and not necessarily the right amount for every house.)
If you correct these problems, you should no longer see ice damming in the winter.
Want to know more about maintaining and protecting your roof? Just ask me, I'll be happy to help.