Ice damming is the #1 winter call we get in Evanston. The fix is rarely a new roof — it's almost always an attic.
The microclimate that makes Evanston special — and ice-prone
Evanston's east-of-Ridge neighborhoods sit in a peculiar lake-effect pocket. From mid-December through mid-March, snow that falls on lakeside Wilmette or south-of-Howard Chicago will often melt off within 48 hours of a sunny day. The same snow on a Lakeshore Historic District Queen Anne can sit on the north-facing slopes for weeks, refreezing every night, slowly building the ice ridge that pries shingles loose and pushes meltwater up under the field.
The reason is partly the city's tree canopy (one of the densest urban forests in northern Illinois) and partly the lake-moderated nighttime temperatures that keep the roof surface in a freeze-thaw cycle longer than the inland suburbs. By February, those repeated cycles have turned every poorly ventilated attic in Evanston into an ice-dam laboratory.
What an ice dam actually is
Heat escaping from the living space below warms the roof deck. Snow on that warmed deck melts. The meltwater runs down the slope until it reaches the cold overhang past the exterior wall, where it refreezes. As the ice builds, it traps subsequent meltwater behind it. That standing water then works its way *up* the roof — under the shingles, under the underlayment if it's old, and eventually through the deck and into the attic, the soffit, and the wall cavities.
Most homeowners try to solve this with roof rakes, electric heat cables, or — most expensively — a new roof. None of those is the real fix.
The real fix is the attic, not the roof
The actual ice dam fix is keeping the roof deck cold so the snow does not melt in the first place. That requires three things working together:
- Adequate intake ventilation at the soffit. Most pre-1960 Evanston homes have nowhere near enough soffit intake. The 1:300 ratio (1 sq ft of net free vent area per 300 sq ft of attic floor) is a minimum; we install closer to 1:150 in tree-shaded north-facing exposures.
- Balanced exhaust at the ridge. Old gable vents and roof-mounted box vents are nowhere near as effective as a continuous ridge vent. A balanced system pulls outside air through the soffit and out the ridge, washing the underside of the deck with cold air all winter.
- R-49 to R-60 of attic insulation, properly air-sealed at the ceiling plane. Ventilation alone cannot overcome a leaky ceiling. The recessed lights, attic hatch, plumbing chases, and top plates of every interior wall must be air-sealed before the insulation goes back down.
When all three pieces are in place, ice dams stop forming on 80 to 90% of Evanston homes — without any roofing work.
When the roof itself does need attention
The remaining 10–20% of cases — homes with cathedral ceilings, structural insulated panel additions, or finished attic spaces with no usable cavity — need the roofing-side defense: extending ice-and-water shield membrane six feet up the slope from every eave (the City of Evanston minimum is three feet; we double it) and re-doing the valleys and sidewall flashings to handle backed-up water.
The "heat cable" myth
Electric heat cables visible on the eaves of many Evanston homes are a band-aid, not a solution. They cost $40–$80 per month in electricity to run, they fail every 3–7 years, and they only melt a narrow channel through the dam without addressing the underlying cause. We will install them when a homeowner insists, but we always recommend the attic fix first.
What an attic ventilation upgrade costs
A typical Evanston single-family home upgrade — new continuous soffit venting, ridge vent, air sealing, and R-60 blown cellulose — runs $4,800 to $7,500. That is significantly less than a new roof, lasts 30+ years, lowers summer cooling costs 8–15%, and qualifies for the Inflation Reduction Act 25C tax credit (up to $1,200 for insulation, with additional credits for air sealing).
If you've fought ice dams two winters in a row, that is the conversation to have — before you spend $20k on a new roof that will dam up just like the old one.