Ice Dams Explained (Why They Keep Coming Back)
Ice dams form when melting snow refreezes near roof edges, creating a barrier that traps water behind it. While often treated as a surface problem, ice dams are caused by internal heat and airflow conditions.
This page explains how ice dams form, why they recur, and why many common remedies fail to prevent them.
How Ice Dams Form
Snow melts on warmer upper roof surfaces. Meltwater flows downward until it reaches colder eaves, where it refreezes and forms an ice barrier.
The Role of Heat Loss
Heat escaping from living space warms roof surfaces. This heat loss is driven by insulation gaps, air leakage, and thermal bridging.
Why Gutters, Rakes, and Edges Freeze First
Roof edges extend beyond insulated wall assemblies. These areas remain colder, allowing refreezing even when upper roof areas are above freezing.
Why Surface Fixes Don’t Work
- Heat cables address symptoms, not causes
- Ice removal does not stop heat loss
- Edge membranes cannot prevent refreezing
Ice Dams and Water Intrusion
Water trapped behind ice dams can back up under roofing materials, leading to leaks, staining, and insulation damage.
| Condition | Impact |
|---|---|
| Uneven roof temperature | Melting and refreezing cycles |
| Blocked drainage | Water backup |
| Extended freeze periods | Persistent ice buildup |
Why Ice Dams Keep Returning
Ice dams recur when underlying heat and airflow conditions remain unchanged. Removing ice does not correct the imbalance.
Preventing Ice Dams Long-Term
Long-term prevention requires managing heat flow, air leakage, and drainage simultaneously. Focusing on one factor alone is rarely effective.