The severe weather most of the country has experienced the past couple of months has demonstrated to many of us what bad things can happen to a house buried under heavy snow. Home inspectors recognize the obvious risk of collapsing roofs but most of us living in the comfy, cozy south are unfamiliar with ice dams. People who’ve lived in snow country are way more familiar with them. Ice dams can damage both the inside and outside of a house or commercial building.
Home inspectors know that ice dams are exactly what they sound like - icy barriers that stop water from flowing and force it to build up behind the dam. Unfortunately, ice dams just happen to form at the edge of the roof. Here’s what happens:
Snow accumulates on the roof of the building, creating another blanket of insulation that holds heat inside the attic. If your house has a warm air leak into the attic, say from a leaky heat duct or furnace flue, it can warm the underside of the roof, melt the snow and cause it’s water to run down to the overhang. There’s no warm air at the overhang so as soon as the water gets there it freezes, thickens into ice and forms into an ice dam that gets thicker and thicker as more water reaches it and freezes. With no place to go, the water gets deeper, eventually backing up under the flashing and lifting the shingles. From there the water can flow into the attic and make its way down into the house where it damages ceilings, walls and other parts of the house.
Preventing an ice dam isn’t rocket science. The smartest way is to have an energy audit that uses infrared cameras to show where heat and cold are accumulating in the house. If it shows a warm area in the attic (or someplace else) you go find out what is causing it and fix it. Most fixes will be inexpensive, usually around $25.00 for some tape or sealer. Keep in mind, though, that some costs can be higher. I know of one audit that showed about ten feet of exterior wall that hadn’t been insulated at all. Watch your footing when you’re in the attic. Home inspectors learned a long time ago to find beams and joists to walk on. If you miss one, your foot or the rest of you will wind up in the living room.
Another preventive measure is a bit more physical – go up on the roof and shovel off the snow. Be careful not to damage the shingles. If the snow isn’t packed down you may be able to clear it off with a push broom (that’s what I used to uncover my cars before I moved to the sultry south). You can also work from a ladder (secured at the eave so it won’t slip out from under you) to hammer or chisel channels in the dam. One caution – BE CAREFUL!!! The roof can be slippery and falling can be really bad for your health. News reports mention two Minnesotans who were killed when they fell from their roof while shoveling its snow cap.
Finally, the safest and most effective way to prevent ice dam damage is to hire a contractor to use low pressure steam to clear channels through the ice dam so the water can flow down instead of up.