Dear Home Work: When we have heavy snows, our roof doesn't totally melt, and an ice dam forms in two areas. Now we are getting leaks through the ceiling. How do we fix this?
Ice dams are caused when heat from the house begins warming the bottom of the snow on the roof. The melting snow runs down the house, until it reaches an area that doesn't receive any heat - like a porch, over¬hang, or eaves. That snow remains frozen, and the melting snow gath¬ers, refreezes, and creates an ice dam.
The melt behind the ice dam backs up until the water finds a way through the shingles, tar paper, sheathing, insulation and drywall. It's not long before cold water begins dripping through the ceiling, and you have a major mess, with major potential damage.
Prevention, of course, is always the most successful way of avoiding ice dams. Good design in snow areas (no flat roofs, steeper angles), prevents the problem. You want the snow to run off the roof, not stay there. Metal roofs are virtually maintenance free from this type of problem.
If it's time to re-roof, and you choose shingles, have your roofer install a rubberized membrane ice and water shield before the shingles go down, on the effected areas. Use this rubberized membrane in all the valleys of the roof as well.
Short of re-roofing, there are sev¬eral options to consider. Make sure the attic (or rafter space if it's a cathedral ceiling) has enough insula¬tion for Big Bear. Ventilate the attic properly. (We've noticed many properties in Big Bear do not venti¬late the attic, but instead try to keep the warm attic, air tight. This may be a trade-off you need to consider). Insulation and ventilation will keep the heat away from the roof and pre¬vent the snow from melting - and in many cases alleviate the ice dam problem.
Another possibility is to install heat coils in a zig-zag pattern over the area above the eaves. This will heat the area and let the snow run off the roof. However, if the electricity goes out, or the coils are broken, the system won't work , but the ice dams still will.