Todd from Washington recently asked me this question about ice dams and metal roofing:
Q: We bought and moved into our house in January. The neighborhood is in a mountain setting and gets a lot of snow. We are new to the area and didn’t really know anything about ice dams. A few weeks after moving in, we had water coming inside the house from melting snow blocked by ice dams on the eaves. We need to get this resolved as we don’t want to be constantly worried about ice dams every winter. We’re thinking about replacing our asphalt shingle roof with metal… to keep the snow off the roof. I realize that there are no guaranties that ice dams will be prevented with any roofing material. The more I read the more confused I get from varying opinions. One opinion is that ice and snow building up in roof valleys could damage a metal roof… much like a glacier breaks up rocks. The metal could buckle from the pressure of the ice building up in the valleys with no other place for it to go. Is this true? Are there ways to prevent this?
Because he has a nice name, I responded quickly. (Not really — I always try to respond quickly.) Here is my response:
A: Thanks for your questions, Todd.
Ice dams occur primarily for two reasons –
Snow melting on the roof from heat inside the home then re-freezes on the overhangs.
Snow log-jams in valleys and other tight areas on the roof and can’t be shed from the roof.
Conditions with extreme cold temperatures and no sunlight can make these situations worse. For that reason, ice dams are often worst on the north side of a building.
Metal roofs can shed snow more quickly and that can be helpful. However, especially in cases of heavy snow and continued cold temperatures with no sunlight, ice dams can still occur on metal roofs.
I would see whether anything can be done to increase insulation on the ceilings in your home, and ventilation between the insulation and the roof deck.
Regardless if you install a metal roof, snow guards in areas uphill of valleys can help prevent the log jamming of snow that can lead to ice dams. On a metal roof, those same snow guards can also help prevent damage to the roof.
I hope this helps. Please contact me anytime.