Ice at the Eaves: Heat Cable, Roof Rake, Ice Belt or Air Sealing, Compared

Paul Fisette of the UMass building-science program names three ingredients of an ice dam: snow, warmth that melts it and cold that refreezes the meltwater. Heat lost from the house warms the upper part of the roof, while the overhang stays cold, so meltwater runs down and freezes at the edge. Deeper snow and colder weather raise the odds, since snow insulates the roof and holds the heat in. The article dates from 2011 and says some of its information may be outdated.

NOAA's 1991-2020 normals for the Newark airport station show a January average of 32.8 degrees Fahrenheit. That month counts 22.6 nights at or below freezing and 7.0 days when the daily high does not rise above freezing. February has 20.0 freezing nights and December 17.5. Yearly snowfall averages 31.5 inches, with 9.1 in January and 10.1 in February. Wikipedia's climate note for Colonia gives a January average of 33 degrees. A January near the freezing line, with snow, is the setup for thaw-and-refreeze cycles. The station is some miles from Colonia, and a given street can differ.

The National Weather Service's summary of the 22-24 January 2016 storm lists 19.0 inches at Woodbridge from a trained spotter, with 27.7 at Metuchen the county's highest. Colonia and Edison are not in that report. The review of 16-17 January 2022 is lighter, 1.0 inch at Hopelawn, though it came with a 66 mph gust. Deep snow is one of the three conditions UMass names, and the January 2016 totals show how deep it can get in the county.

UMass advises against heat cable, saying it creates an ice dam just above it, and not to waste time or money on it; heat tape also wastes energy and can damage shingles. Removing ice with tools or chainsaws, the article says, does more harm than good. Both jobs put someone on a ladder or at the roof edge, and NIOSH puts the U.S. toll from ladder falls above 100 a year. On a flat roof, the Asphalt Roofing Manufacturers Association lists membrane damage from ice movement among the effects of standing water.

Careful raking of snow off the lower roof helps, according to UMass, and NIOSH tells anyone working near utility lines to keep at least 10 feet away. Ice belts often fail when a secondary dam forms above them, and self-adhering membranes under the shingles act as a backup layer the author calls a band-aid. New Jersey's Bulletin 07-3 ties the code's ice-barrier requirement to an average January temperature of 25 degrees or colder, a description it matches to Sussex County. Colonia is outside it, though a roofer may add a membrane at the eaves anyway.

UMass names a cold roof as the ideal remedy, with the whole roof held at outdoor temperature. In the article's order, warm air is sealed out first, at wire and plumbing penetrations, light fixtures, attic hatches, chimneys and bath fans; then insulation goes in, roughly R-38 for northern homes, continuous over the exterior walls; then soffit-to-ridge ventilation with baffles and a 2-inch air channel above the insulation. The Department of Energy's brief likewise prefers baffled ridge vents. The article adds that after a dam, wet insulation, damp roof boards and moisture in the wall cavity can cause rot, mold and peeling paint even once the ice has melted. The EPA's mold page says to dry wet materials completely. The Census median house in Colonia dates to 1959, so what a hatch shows about insulation depth is worth noting.