Ice dams on a Clay, NY house: when the town's temperature swings hit the eave

The Clay section of the county hazard plan ties the town's ice exposure to irregular temperature swings. Swings across freezing give an ice dam many chances to form: meltwater runs down a warm roof, refreezes on the cold overhang and holds more water behind it. The Department of Energy describes that mechanism, and the code answers it with an ice barrier at the eave where ice has formed there before.

Northern Onondaga County records more freeze-thaw crossings than the airport does. The NOAA station at Brewerton, in the north of the county, shows about 109 against about 84 at Hancock airport. Treat that as background on the north county and not a count for your street.

What it means for you is simple: the eave of a Clay house sees a lot of cycling, so the barrier and the drip edge matter more than a quote that skips them suggests.

Look at the roof from the street on a cold morning after a thaw. Ice sitting only along the lowest edge, with bare shingles above it, is the classic picture. Note which sides of your house it appears on and whether the garage or porch roofs show it too. Those notes tell your roofer where to start.

Most homes in Clay are detached houses, and the median was built in 1978. Code asks for an ice barrier at the eaves where ice forms, but a roof laid decades ago may have been done to an older standard. Ask what is under the shingles at the lowest course and how far the roofer proposes to run a barrier.

The barrier is cemented double underlayment or a single self-adhering sheet, and it reaches at least 24 inches inside the wall line. Ask the roofer to put the distance they plan for your house in your estimate.

Ask too whether the drip edge will be new. The code asks for one on every shingle roof, and it is easy to leave off a cheaper job.

On roofs 8 in 12 or steeper the barrier also runs 36 inches up the slope, so a steep front gable may need more than a low ranch roof. Have the number written next to each part of the roof it applies to.

March has more freeze and thaw crossings than January in Syracuse, so a stain that appears in March and fades by May is consistent with the eave. Write down the dates you see it. Tell your roofer, because the pattern you saw is evidence.

You want two prices, one for rebuilding your eave and one for a full replacement. Boards at a wet or spongy edge belong in the eave price. If the roof above is sound, your edge may be all you need.

The Department of Energy traces the upstream cause to warm air reaching the deck, which is separate from the roofing. Ask the roofer whether they see signs of it, then decide.

If water drips in during a thaw, move what is under the stain and photograph the ceiling before anyone touches it. A roofer who sees the stain undisturbed can read it better.

Finally, ask for the roofer's read on the lowest rows of shingles as they come off. If the boards under them are dark and soft, the eave job grows to include them. That is the moment to find out how the roofer prices boards, so ask before the work starts. Tell us the room and the weeks you see the stain, and ask for the eave price first.