What 30 Years of Wilmette Roofing Has Taught Us About Ice Dams: Why They Form, How to Prevent Them and When the Roof Itself Is the Real Problem
30 years of Wilmette roofing has taught us a lot about ice dams. Here's what causes them, how to prevent them, and when the roof itself is the real problem.
Wilmette's specific ice dam pattern
Ice dams are a Chicagoland-wide issue, but Wilmette gets hit harder than most North Shore communities for two specific reasons: lake-effect snow events deliver meaningfully more snow accumulation than 5-10 miles inland, and the mature housing stock in Kenilworth Gardens, Indian Hill, CAGE, East Wilmette, and Hibbard Woods includes a high concentration of original-construction homes from the 1920s-1950s with attic insulation and ventilation systems that don't meet current standards. The result: most Wilmette neighborhoods have a meaningfully higher rate of ice dam formation per winter than the suburbs to the west, and the older homes in particular form dams every year that has more than 12 inches of cumulative snow. Over 30 years of working Wilmette roofs, we've developed a clear picture of why this happens and what to do about it.
Why ice dams form (the actual mechanism)
Ice dams form when attic heat escapes upward through the roof deck, warming the underside of the snow accumulation on the roof. The snow at the warmer central roof area melts; the meltwater runs down toward the colder eaves; at the eaves — which sit over an unheated overhang and stay at ambient outdoor temperature — the meltwater refreezes. This forms a wall of ice along the eave line. Continued melting upslope produces more meltwater, which pools behind the ice dam and gradually backs up under the shingle courses. Asphalt shingles are designed to shed water flowing downhill, not to hold back water pooling behind them. The pooled water finds its way through fastener penetrations and under shingle laps, into the decking, through any gaps in the ice-and-water shield (or where ice-and-water shield was never installed in the first place), and ultimately into the attic and ceiling. The damage is invariably interior, and the leak typically appears 4-8 weeks after the ice dam first formed.
What you can do without touching the roof
Attic insulation: most Wilmette homes built before 1980 have R-19 to R-30 of attic insulation. Current Illinois code is R-49 for attic insulation. Adding insulation to meet current code reduces heat loss through the ceiling and is the single highest-impact intervention. Air sealing: gaps around recessed lights, attic hatches, plumbing penetrations, and bathroom exhaust fan housings let warm humid air directly into the attic, bypassing the insulation entirely. Sealing these gaps with closed-cell foam and gasket kits is high-impact and relatively low-cost. Soffit ventilation: many older Wilmette homes have soffit vents that have been blocked by blown-in insulation over the decades. Restoring soffit-to-ridge airflow allows the attic to stay closer to outdoor temperature, which reduces the temperature differential that drives ice dam formation. These three interventions — insulation, air sealing, ventilation — solve ice dam problems on roughly 60% of Wilmette homes we've worked on without any roof-side work.
When the roof itself is the problem
On the other 40% of Wilmette homes, even with optimized attic insulation and ventilation, ice dams still form because of roof-specific issues. The most common: missing or inadequate ice-and-water shield at the eaves. Modern Illinois code requires ice-and-water shield to extend from the eave edge to at least 24 inches inside the heated wall line. Many older Wilmette homes have a 6-inch ice-and-water strip at the eave or none at all. Without adequate ice-and-water shield, even a small ice dam produces a leak. The fix is roof replacement (or strip-back-and-replace) with proper ice-and-water coverage — typically 36 inches up from the eave, which provides a meaningful margin. The second common roof-side issue: low-slope roof sections (porches, additions, dormers with shallow pitch) that don't shed water well even without ice damming. These often need a different system — either a continuous membrane (modified bitumen or TPO) or a transition to a steeper pitch in a major remodel — to fully solve the leak problem.
The hand-shoveling-the-roof debate
Every January we get calls from Wilmette homeowners asking whether they should physically remove snow from their roof to prevent ice dams. The short answer: yes, but carefully, and only with the right tool. A telescoping roof rake used from the ground to clear snow from the lower 3-6 feet of the roof above the eave line reduces ice dam formation effectively. Walking on the roof in winter to shovel snow off is dangerous (icy surfaces, hidden roof damage, fall risk) and frequently damages shingles. Hiring snow-removal contractors who walk the roof with shovels is acceptable in extreme cases but expensive and not without risk. The roof-rake-from-ground approach is the right answer for most Wilmette homes. Even better: solve the underlying insulation and ventilation problem so snow doesn't melt asymmetrically in the first place.
When ice dam damage means roof replacement
We see meaningful interior water damage from ice dams on roughly 5-10% of Wilmette homes we assess in any given spring. When the damage has been recurring for multiple winters, the cumulative damage to the decking, framing, and interior finishes typically warrants full roof replacement with proper ice-and-water shield rather than ongoing repair. The conversation we have with these homeowners: 'You can spend $4,000-$8,000 a year fixing ice dam damage, or you can spend $30,000-$60,000 once on a properly-specified replacement that includes adequate ice-and-water shield, improved attic ventilation, and Class IV impact-resistant shingles for the inevitable hail event coming sometime in the next 25 years.' Most homeowners conclude the replacement is the right call. Roof replacement, attic insulation, and attic ventilation are all core services.
Get a Wilmette-specific ice dam assessment
Every Wilmette home is different. The right intervention — insulation, air sealing, ventilation, roof replacement, or some combination — depends on the specific home's construction, insulation history, ventilation system, and roof condition. We've worked Wilmette ice dam problems for 30 years and can give you a straight read on which intervention is right for your specific home. Call (708) 847-5418 or use our contact form for a free Wilmette ice dam assessment.