After a long stretch of mild winters, we have now faced two winters in a row where conditions were rife for the formation of ice dams. If you are interested in causes and fixes, please read my article from last year, “What’s to be Done About Ice Dams”. The advice there is still sound. To summarize, get your attic cooled down by re-insulating, sealing heat by-passes and making sure your attic ventilation system is working. If these steps are impossible or don’t help, your only real solutions are to install some sort of heat coil system or remove snow from the roof as it falls.
What I want to address in this article is the apparently pervasive notion that if your sloped roof leaks because of an ice dam, there must be something wrong with the roof. Of course I’m not trying to say that every roof everywhere has been installed correctly (just the ones put on by ABC). I’m also not trying to say that some installation errors can’t contribute to ventilation problems and worsen the leaking caused by ice dams. The point I want to emphasize is even the best installed, most up to code roof that used the finest quality roofing products know to man will still leak if enough water gets backed up behind an ice dam.
Sloped roofs are designed to shed water and melting snow. They are not designed to act as a pool liner. Ponding water on a roof will find its way in eventually. No amount of flashing, water-resistant underlayments or caulk will help. Maybe someday someone will invent a roofing system that addresses this problem and when they do, we’ll be first in line to install it, but, so far, no one has come out with one. In fact, no manufacturer of roofing products anywhere will warrant their products against leaking caused by ice dams.
Perhaps the most often cited yet least understood product with regard to ice dam problems is the so-called “Ice and Water Shield”. This is the self-adhering, modified bituminous sheet that is used as a shingle underlayment which building code requires be installed along eavelines and in valleys in northern climates. The idea of the product is that if water does somehow get under the shingles, this waterproof membrane will keep it above the decking and out of the building envelope. It in no way prevents or lessens the formation of ice dams. As for its ability to prevent leaks, remember the product is installed under the shingles and the shingles are nailed through the roof deck, so even correctly installed Ice and Water Shield has hundreds of nail holes through it. While it may help keep water that backs up under the shingles from leaking into the house, it is not a fix-all or miracle product that some purport.
The second biggest ‘usual suspect’ is flashing. Just so we are on the same page, when I say flashing I am referring to the use of metal to protect an especially vulnerable part of the roof (e.g. roof/wall connections, valleys, skylights, chimneys). The thing about flashing is, like the rest of the roof, it is only designed to work with moving water, traveling in one direction, down the roof slope. The second the water becomes static or begins to move back up the slope through accumulation, the flashing stops functioning and can easily fail. This is any flashing, even brand new, high quality, correctly installed metal. Again, maybe some day there will be a better system and, when there is, we’ll buy it and install it, but until that time, we can only work with those products available to us.
I understand that when a roof experiences a leak the most common reaction is to blame the company that installed it. I would even say you should probably have them out to take a look at it, but understand that it’s entirely possible that your roof is fine and the leak is just an unavoidable consequence of an ice dam. Ice dams start with heat loss in the attic and are exacerbated by poor attic ventilation. If your roofer correctly installed an adequate amount of attic exhaust vents, there is really nothing more that can be done to ward off ice dams during a typical roof installation. That is why no reputable roofing company will warrant against ice dams. If your roof only leaks when there are ice dams upon it (and doesn’t leak when it rains), chances are there is nothing wrong with it. No matter how well installed, a roof may still leak if enough water gets backed up behind an ice dam on it.