Ventilationand ice damsthe cure is below the roof.

Ice dams form when heat escaping from the house melts snow partway up the roof, the meltwater runs down to the cold overhang and refreezes there, and the ridge of ice that builds up backs water under the covering. Ice-and-water membrane at the eaves means that water cannot get into the house, which is why we install it — but the dam is still forming, still prising at the gutters and still loading the overhang. The actual cure is upstream of the roof entirely.

That means two things working together. Air sealing the ceiling plane — recessed lights, the attic hatch, top plates, every pipe and wire penetration — so warm air stops leaking into the attic in the first place. And balanced ventilation, with intake at the soffits and exhaust at the ridge in roughly equal area, so whatever heat does get up there is carried away before it can warm the deck. Exhaust without intake is the commonest fault we find: a ridge vent with blocked or insulated-over soffits simply pulls conditioned air out of the house.