Ice Dams: Why They Cause Leaks & How to Stop Them

Ice dams cause leaks when snow melts on warmer roof sections then refreezes at the colder eaves, trapping water that seeps under shingles and into attics or walls. In Longmont this cycle repeats during the snowy winters common across Boulder County, especially on homes with poor attic insulation.

Why Ice Dams Form on Longmont Roofs

Longmont's semi-arid climate brings warm summers followed by cold, snowy winters that create ideal conditions for ice dams. Heat escaping from attics melts snow on upper roof planes while the overhangs stay below freezing, causing meltwater to refreeze at the edge. Older housing stock in Downtown Longmont and Old Town often has thinner insulation and more air leaks, which worsens the temperature difference. Left Hand Creek and Roosevelt Park areas see similar patterns because many homes sit on north-facing slopes that hold snow longer. The result is a ridge of ice that acts like a dam, backing up water behind it for days or weeks until it finds a path under the shingles.

How Ice Dams Lead to Roof Leaks

Once the ice ridge forms, water has nowhere to go except sideways or upward under the shingles. In Longmont this commonly occurs at valleys, around chimneys, and near skylights where flashing is older or less effective. Water then reaches the roof deck, soaks insulation, and drips into ceilings or walls. Homes in Kensington and Sunset neighborhoods report repeated leaks in these spots after heavy snow because many roofs are 15–25 years old and the underlayment has aged. The process can continue even after the storm ends if daytime highs reach the 30s while nights drop below freezing, allowing repeated melt-refreeze cycles.

Practical Steps to Stop Ice Dams

Improving attic insulation and sealing air leaks at penetrations reduces heat loss that drives the melt-refreeze cycle. Homeowners should also keep gutters clear of debris so water can drain freely rather than pooling and freezing. Installing roof-edge heat cables provides a targeted melt path along the eaves where dams form most often. In neighborhoods like Sunset, CO, many residents add extra underlayment during re-roofing projects to create a wider ice barrier. Regular checks after storms help catch small ridges before they grow into larger problems that reach interior spaces.

When Professional Ice Dam Removal Helps

When dams reach several inches thick or leaks have already started, safe removal requires roof rakes or steam equipment rather than chopping that can damage shingles. Ice Dam Removal & Prevention crews working in Longmont focus on the lower roof edge without stepping on fragile ice. Pairing removal with an inspection catches any new entry points created by the water. For active leaks, Emergency Roof Leak Repair teams can apply temporary measures until permanent fixes are possible. Readers can also review the Longmont Seasonal Roof Maintenance Checklist (Spring/Fall) for year-round habits that limit ice dam formation.