Extend the ice and water shield at least three feet above the interior wall line where ice dams are likely to form.

For cold climates the practical thumb rule is to carry the ice barrier a full three feet above the exterior wall line or at least two feet beyond the eave when roof geometry or detailing prevents the full three feet extension. Start by identifying the interior wall line from the attic ceiling or framing plates and mark that line on the roof so the membrane covers the area above it. Overlap each sheet by the manufacturer recommended amount and seal laps with roofing cement where wind or driving snow are concerns. Always run the membrane up and over valley flashings and around dormers and penetrations to create a continuous waterproof plane on critical sections. Combine this membrane extension with improved attic insulation and balanced ventilation to keep the roof sheathing cold and minimize meltwater production on the roof surface. When using metal drip edges or specialty flashings, fasten through the membrane only where permitted and seal fastener penetrations to keep the barrier continuous.

The three common mistakes are stopping the membrane at the eave which leaves the area above the wall vulnerable, relying solely on membrane without improving attic insulation and ventilation, and failing to extend the barrier through valleys and around penetrations which creates leak paths. If the membrane is stopped at the eave extend it up to the marked interior wall line to cover the likely ice dam zone. If attic heat is still causing melt pair the extended barrier with added insulation and a ventilation strategy to reduce heat transfer to the roof deck. If valleys and penetrations are left exposed remove loose shingles, integrate the membrane under valley flashings and detail around pipes and vents so the membrane ties into the flashing.

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