Up on the roof

On the roof, it’s peaceful as can be . . .

James Taylor never experienced ice dams. Through the years I’ve become an expert on these frustrating winter constructions. For the uninitiated, ice dams occur when the snow on your roof melts from the bottom due to the space beneath your roof being warmer than the outside air. The water that results from the melted snow rolls down the shingles until it hits the part of the roof that extends over the soffet. (The soffet is the overhang that juts out from the exterior wall of your house). Because the soffet is extended over the outside air, it’s cold. When the melted snow hits that part of the roof it freezes, with some cascading over the edge to form ever lengthening icicles. The frozen ridge of ice at the edge of the roof creates a literal dam, blocking the path off the roof for the rest of the melting snow. This causes the dam to get higher and wider. Pretty soon, the melted snow starts backing up over the warm part of the roof where it works its way beneath the shingles and into your house. It often starts as a drip, drip, drip from a ceiling light fixture or a big wet spot on you ceiling. It’s very annoying.

The immediate action for water coming in, once buckets are in place, is to open up a gap in the ice so the water can drain off. If the roof is above the first floor, it’s best to hire someone to do this for you. There usually they’ll take a hammer and hack away at the ice until it chips off. Another approach is to dump chemical snow melt along the edge of the roof and let it do its work. You can fill up a tube sock with the stuff and leave it laying across the ice where it will melt a channel through it.

Removing the snow from your roof will solve the problem, at least until the next snow storm. With no snow to melt, there will be no water backup. I’ve used “snow rakes” before – they’re the long-handled contraptions with a blade at the end, designed to allow you to stand on the ground and pull snow off. I’ve found that removing only a few feet of snow from the edge only pushes the ice dam further up the roof, so in my experience, it’s all or nothing.

There are several long term solutions. Heated wires that you place in a zigzag pattern along the edge of the roof and plug into an outside outlet as needed have worked pretty well for me. They’re easy to install and keep channels through the ice open for water to drain. If you’re replacing your roof, consider installing ice/water shield, a rubberized coating that usually is placed on three feet along the edge, over the entire roof. The experts will say ensure your attic is well insulated and well ventilated so that it’s temperature will remain the same as the outside air and stop melting the roof snow from below. I think if you had a warm roof to begin with, you’ll always have a warm roof.

It’s frustrating. The only real solution is spring. Until then, we can always listen to JT.


3 Responses to Up on the roof

  1. kad barma says:

    The extension of the roof beyond the exterior wall is generally referred to as the “eave”. The soffit is technically just the underside of the eave. Many newer roofs employ a soffit vent that allows cold air to travel up inside the eave, so that the snow on the shingles doesn’t melt to water and start the damming process. (A good modification for the spring if you’re ambitious).

    Calcium chloride in panty hose or a tube sock is a good way to attack an existing dam. Often, the rough surface of the shingles means that trying to knock off the ice frozen upon it with a hammer or other tools will also damage and knock off pieces of the shingles with it. Of course, when the water is pouring through the roof, this is often also the lesser of two evils.

    “Dam proof” roof strategies include metal roofs at a high pitch (those pointy houses in VT aren’t by accident) though soffit venting (with an accompanying ridge vent at the top to complete the pathway for the cold outside air underneath the roof) can do a lot on a lesser-pitched and shingle-clad surface. One other useful design/build/repair technique is to take a roll or two of Grace Ice and Water Shield and cover the first 3 feet (6 feet is better) of the roof beneath the shingles, so that even if dams occur and the water backs up, it backs up onto a waterproof barrier and doesn’t make its way into the house.

    Other techniques include constant raking (you can buy roof rakes with lightweight handles long enough to reach even second-floor roofs from the ground) or the installation of an electric warming wire that can melt the dam before it starts to form.

    Mostly, I’d recommend downtown mill building condo living, but, hey, that’s just me!

  2. Paul@01852 says:

    According to the Globe Handyman the rubberized ice/snow shield is now installed under the shingles over the ENTIRE roof! According to him the original rule was 3′ but then the ice dams just started 3′ higher up so they went to 6′! Same problem!! So now the rule is a minimum of 12 ‘ which on most roofs is the entire thing!

  3. DickH says:

    Thanks for clarifying the roof nomenclature. I had ice and water shield installed over the entire portion of one small section of the roof – it has a shallow slope and is tough to insulate. So far it’s worked fine, but some water was infiltrating along the edge I think through the soffit vent which would seem to defy gravity. I stuck some heated wires up there last weekend. It seems to be working.