Why do I get ice dams and icicles every winter?

What is actually happening up there

Snow lands on a roof and, if the roof is cold all the way across, it sits there and eventually slides or evaporates. Nothing happens.

A dam forms when the roof is not cold all the way across. Heat leaking out of the house warms the deck over the living space, and the snow lying on that part melts from underneath. The meltwater runs down the slope until it reaches the eave, which overhangs open air and is therefore genuinely cold, and there it freezes again. Do that for a few days and the refrozen ice builds a low wall along the edge.

After that the roof is holding water rather than shedding it. Water backs up the slope behind the dam, finds the laps between shingles, and goes under them — because shingles are lapped to shed water running downhill, and nothing about them is built to hold water sitting still. It appears inside as a stain on a ceiling, usually some distance from where it got in.

Why the gutters get blamed

The icicles hang off the gutter, so the gutter looks guilty. It is not.

A gutter full of ice is downstream of the problem, not upstream of it. Cleaning it, replacing it, enlarging it or adding guards changes what the edge looks like and changes nothing about the heat coming up through the ceiling. Plenty of houses have had new gutters fitted twice and still stain the same corner every February.

The same goes for standing in the driveway with a roof rake. Pulling the snow off the lower few feet takes the fuel away for a week, and it is a reasonable emergency move, and it is not a repair.

The gutter is where you see it. It is almost never where it starts.

The things that are usually wrong

Air leaks

Gaps where warm indoor air escapes straight into the attic: around the attic hatch, recessed lights, plumbing stacks, wiring holes, the chase around a chimney, the top plate of interior walls. Air carries far more heat than conduction through insulation does, which is why sealing usually beats adding.

Insulation that is thin or in the wrong place

Or compressed. Or laid neatly across the middle and stopping short at the edges, which is exactly where it matters most for this.

Blocked intake at the eave

Soffit vents stuffed with insulation are extremely common. Without intake at the bottom, a ridge vent at the top has nothing to pull through and the attic does not flush.

Fans venting into the attic

Bathroom and kitchen fans that stop inside the roof space instead of going outside. Warm, wet air, delivered directly to the coldest surface in the house.

Ductwork or a furnace in the attic

Uninsulated or leaking ducts heat the space they run through. On a cold night that is a heater pointed at the underside of your roof.

A finished space up there

Attic conversions and cathedral ceilings remove the buffer a vented attic used to provide, and they have to be detailed carefully to keep a cold roof cold.

Where the roof itself comes into it

There is a roofing answer, and it is a second line of defence rather than a cure.

Ice barrier is a self-adhering membrane laid over the deck at the eaves before the roof goes on. It seals around fasteners, so when water does back up behind a dam it meets a sealed surface instead of a lapped one. Rhode Island's code carries requirements for it at the eaves on new roofing, which is a fact about the state's code rather than about any particular job — what applies to yours is confirmed with the town.

It matters, and it should be there. It also does nothing to stop the ice forming. A house with a properly protected eave and an attic full of escaping heat will still grow a dam every winter; it will simply take longer to leak. If someone proposes a new roof as the fix for ice dams and has not been in your attic, that is worth a second opinion.

What it costs you to leave it

It is easy to treat as a seasonal annoyance, because for a while that is all it is.

What happens slowly is that the deck and the framing at the eave stay wet through the winter and dry out in the spring, year after year, which is the condition rot likes best. Insulation that gets wet loses most of its value and does not recover. Wet cavities grow mould where you will not see it until something is opened up. Gutters and fascia get torn off by the weight. And falling ice is a genuine hazard over a doorway or a path.

None of that is dramatic in any one winter, which is the problem with it.

The order to fix it in

1. Go up and look, on a cold day

   Ideally with snow on the roof. Frost on the underside of the sheathing, a warm patch, daylight through a soffit, a fan duct going nowhere — the attic tells you most of it in ten minutes.

2. Seal the leaks

   Air sealing first, because it is usually the cheapest step and the one with the largest effect. Adding insulation over an unsealed ceiling buries the problem rather than fixing it.

3. Insulate properly, and to the edge

   Including the attic hatch, which is frequently the worst single spot in the house.

4. Restore the airflow

   Clear intake at the eaves, baffles to keep insulation out of the path, and exhaust at the ridge that is actually connected to it.

5. Deal with the roof when it is next replaced

   Ice barrier at the eaves, edge detail, flashings. Doing it at replacement time is sensible; replacing a sound roof in order to get it is usually not.

What to ask whoever you call

Ask them to go into the attic before they quote anything, and be wary of anyone who will not. The evidence is up there and the diagnosis costs an hour.

Ask what they think is causing it, in plain words, and see whether the answer involves heat and air or only shingles. Ask what they would do in what order. Ask whether heated cables are being proposed as a fix or as a way to manage the symptom while the real work waits — both are legitimate answers, and only one of them is honest about what it is.

Then get it in writing before you sign, including what is not included. If more than one trade is involved — insulation, ventilation, roofing — ask who is holding the whole thing together and who you call when one of them does not turn up.