Archived Articles

Winter 2011

Why do I have a roof leak? In the middle of winter?!

What is happening with my roof? It hasn’t happened before until this year!

We have had many calls on this situation, this year in particular. Homeowners are experiencing roof leaks. Some have just installed a new roof and are frustrated. It is always unsettling when we have a steady drip in our house that we can’t seem to explain or stop.

Truth is, it is in fact a roof leak, but not due to a deficient roof. The phenomenon of ice damming is primarily to blame. Everyone has heard or read to some extent about ice damming and have rarely ever experienced it with their homes. This year is different due to different circumstances, one being the amount of snow we had within a short period of time at our first snowfall.

Eave protection against ice dams

First off, sloped roofing is not meant to be entirely waterproof. It is a system that is meant to shed water, not to act like a “swimming pool liner”.

This year’s difference is the amount of snow we had at once when fall turned to winter within two days. We all had roughly 12 to 14 inches of snow on our roofs within days. Snow is, in fact, a decent insulation. It has an R Value of approximately R-1 per inch. So think of your roof as having a layer of R12 insulation on the exterior. The snow directly in contact with the roof is within prime condition to melt with any heat loss from the heated living space. Poor insulation and poor ventilation of attic spaces allow for warm air from the house to linger in your attic space and help the roof sheathing (plywood of plank surface holding your shingles) stay warm causing the snow above to melt and trickle down underneath the thick layer of snow on your roof. Also, in areas where the attic insulation is in direct contact with the roof sheathing (like at the eave area), heat conduction is present warming the sheathing to a certain extent. Once that trickle of water hits the cold eave beyond the exterior wall of the heated living space, it re-freezes due to the fact that the eave is not over a heated area. Continue this process, and eventually an ice wall is formed along with icicles at your gutters. Continue the melting snow issue hitting the ice wall at the eave and we have pooling water, still under that R-12 to R-14 layer of “snow insulation”. This water will have no where to go but past the roofing material. Remember that a roof is never completely waterproof. A 3 to 4 foot layer of waterproofing membrane at the eave of new roof installations is required now because of this phenomenon. Proper installation of this membrane is still crucial so it can function as intended. Still, if the water pooling goes beyond that membrane, seepage is still probable.

The pooling water is in most cases just over the top of your exterior walls. In some cases you might find that windows and doors are leaking from the top horizontal trim. This is due to water travelling through the exterior wall and finally getting through at the trim. In worse cases, the water can travel down an exterior wall cavity and only re-appear at a lower floor wall or ceiling.

What is the solution?

Your roof is probably not the issue. Easiest 1st step is to clear the snow off your roof. Keep you roof cold.

Another way to keep your roof cold is to provide proper insulation and ventilation in all attic spaces. Remember that 1 ½ and 2 ½ storey homes have, in most cases, many attic areas above and behind knee walls. They should all have proper insulation and ventilation to ensure the attic is kept as cold as possible summer and winter.

PROPER AIR SEALING IS CRUCIAL. This is often taken for granted or ignored. Warm humid air can easily go through any porous insulation material, such as fibreglass insulation, if it has no vapour barrier and/or caulking. It also finds its way into attics through attic protrusions such as plumbing stacks, chimney chases, electrical light boxes/pot lights and wire penetrations, etc. As soon as warm humid air from our homes enters a cold attic, it turns into frost, condensation and helps the melting process of the snow adjacent to the roof material

Preventing ice dams with ventilation

With proper insulation, ventilation and air sealing of your attic spaces, ice damming could be dramatically reduced. This could reduce the effect of ice damming causing interior leakage. So if you are experiencing this in your home, your best bet is to call an insulation contractor before a roofing contractor. Ensure that your insulation contractor thinks outside the box and considers air sealing and ventilation and not just insulation levels.