Clean Gutters Are the Cheapest Ice Dam Insurance You Can Buy

We steam ice dams off roofs every January, and nine times out of ten the gutter under the dam is packed solid with last fall's leaves. Here is the connection, and the one weekend job that breaks it.

How a clogged gutter starts a dam

Snow on the roof melts from the heat escaping your attic. The meltwater runs down to the eave, where it is cold because there is no heated space below. If the gutter is clear, most of that water drains away before it freezes. If the gutter is full of leaves, the water pools, freezes solid, and becomes the foundation for the dam. The next round of meltwater hits that ice wall, backs up under the shingles, and ends up in your bedroom ceiling.

Timing matters

Clean gutters in late October and you will refill them with November leaves. In Greater Boston the right window is after the oaks finish dropping, usually mid-November, and before the first real snow. If you have a lot of trees, a second pass in early December is worth it.

While you are up there

• Run a hose down each downspout to confirm it drains. A clogged downspout is as bad as a clogged gutter.
• Check the gutter pitch. Standing water in a clean gutter means it has sagged and needs re-hanging.
• Look at the drip edge and the first course of shingles. Lifted or missing drip edge is where backed-up water gets in.
• Look for ice and water shield. Newer roofs have it along the eaves; older ones do not, and those are the roofs that leak when a dam forms.

Gutter guards: yes or no

They reduce cleaning but do not eliminate it, and some types make ice dams worse by holding a sheet of ice right at the roof edge. If you install them, pick a style that sits below the roofline, not above it, and still check them each fall.

Gutters are half the story

Clean gutters stop the water from pooling. They do not stop the melting. If you get a dam every year, the real fix is in the attic: air sealing, insulation to current code, and ventilation. That is a fall project too, and it lowers the heating bill while it is at it.