The heat that wrecks the roof is not yours
Rhode Island has more of its housing in two- and three-family buildings than almost anywhere. That single fact explains a failure most owners here are told is a roofing problem, and it is not: the heat that ruins the roof belongs to someone who does not pay for it.
- 1 The ridge. One ridge over two households, and one of them pays to replace it.
- 2 The field. The part everyone looks at, and rarely the part that actually failed.
- 3 Valleys. Most of them were cut in later, when the house was divided into flats.
- 4 The chimney. Often two of them, and often neither one carries anything any more.
- 5 Penetrations. Two kitchens and two bathrooms mean twice the holes on the same roof.
- 6 The overhang. Where heat from a flat you do not control comes back down as ice.
What is actually happening up there
Snow sits on a cold roof and stays. It only becomes a problem when part of the roof is warm and part of it is not — and that is exactly what a heated top floor does. Warm air rises into the space under the deck, the snow above it melts, the water runs down the slope, and it reaches the overhang.
The overhang is not over heated space. It is over outside air, and it is cold. The water refreezes there, builds a dam, and the next melt backs up behind it and goes under the covering. That is the whole mechanism, and none of it starts with the shingle.
Why it is worse in this housing than in a single-family house
In a house you own and live in, you control the thermostat and you feel the draughts. In a building with tenants above you, or with an owner living below, the heat in the top flat is set by whoever lives there — often high, often with windows open in February, and always without any consequence they can see.
The people who pay for the roof are therefore not the people producing the heat that destroys it. Nobody in that arrangement is being unreasonable. It just means the building is warmer under the deck than a single-family house on the same street, and its eaves ice up while the neighbour’s do not.
What a real fix looks like
Three things, and only one of them is roofing. Air sealing between the top ceiling and the roof space, so heat stops arriving in the first place. Insulation that does not block the intake at the eave. And exhaust sized to match the intake, so what does get up there leaves.
On the roofing side, a membrane that runs well past the wall line at the eave. Not the minimum strip: past the point where the heated space ends, which on these houses is further up than the code minimum assumes.
A contractor who quotes only the covering on a building like this is quoting the symptom. Ask directly what the plan is for the heat, and listen for whether the answer involves the attic at all.