Ice dams and eavestrough: what London homeowners should know

What is an ice dam, exactly?

It needs two things: snow on the roof and warmth underneath it. Heat that gets into the attic warms the roof deck from below, and the snow sitting on that part of the roof melts, even on a day that stays below freezing outside.

The meltwater runs down the roof until it reaches the eave, the part of the roof that hangs out past your wall. There is no heated house under the eave, so it stays as cold as the air. The water freezes there. Do that for a few days and the ice builds into a ridge along the edge of the roof: the dam.

The dam is the problem, not the icicles. Once the ridge is there, the next lot of meltwater runs down, hits it and has nowhere to go. It pools behind the ice. Shingles are built to shed water running downhill, not to hold back standing water, so that pool can work its way up under the shingles and into the roof deck, the attic, and sometimes the ceiling or walls below.

A London winter is good at making them. Snow that sits on the roof for weeks, and days that swing around freezing, give the melt-and-refreeze cycle plenty of chances to run.

Why is your eavestrough usually the victim, not the cause?

Because the dam forms on the roof, above the eavestrough, for reasons that start inside the attic. Ice dams form on houses that have no eavestrough at all. Taking yours down would not stop the heat getting into the attic, and it would not stop the snow melting.

That is worth saying plainly, because eavestrough gets blamed for ice dams all the time, and the blame sells a lot of the wrong fixes. New eavestrough on a house that loses heat into the attic will ice up the same way the old one did.

The eavestrough can make things worse, though. A run that has lost its slope holds water in a low spot, and that water freezes in place. A downspout that is clogged or frozen leaves the whole run full. Either way, the eavestrough fills with ice and becomes a solid shelf at the edge of the roof, which gives the dam something to build on. So the honest version is this: the attic causes the dam, and eavestrough that does not drain can help it grow.

What does ice do to eavestrough, hangers and fascia?

This is where the eavestrough pays for a dam it did not cause. After a hard winter, look for these:

• The run pulls away from the house. Ice is heavy, and eavestrough packed with it puts that weight on the hangers that hold it up. The fasteners hold onto the fascia board, and under enough load they work loose or pull out, so the run sags or tips forward.
• Bent or split sections. Ice expands as it freezes. It can push the front edge of the eavestrough out of shape and open up the seams and corners of a sectional run, which then drip all the next spring.
• Downspouts that freeze solid. A downspout full of ice cannot drain anything, and the meltwater backs up into the eavestrough above it. Elbows and joints can split.
• Soaked fascia. Meltwater that backs up behind a dam, or spills behind a sagging run, runs down the back of the eavestrough onto the fascia. Wood that stays wet rots, and rotted fascia cannot hold a fastener. That is the start of a loop our guide on rotted fascia and soffit walks through.

A run that has sagged also tends to sag in the same spot every year, because water collects there, freezes, and adds weight where the hangers are already weakest. If yours is already dipping or pulling away, here is what causes eavestrough to sag and what fixes it.

What actually prevents ice dams?

Keeping the roof deck cold, so the snow on it does not melt from below. That is mostly an attic job, and we would rather tell you that than sell you eavestrough to fix it.

Attic insulation and air sealing. This is the root fix. Warm air leaking up from the house through gaps around light fixtures, the attic hatch, plumbing and wiring carries a lot of heat with it, and too little insulation lets more through. An insulation contractor or an energy auditor can tell you where your attic is losing heat. It is not our trade, and it is the part that matters most.

Attic ventilation. A ventilated attic draws cold outside air in low, through the soffit, and lets it out high, through vents at or near the ridge. That moving air keeps the underside of the roof close to the outside temperature. If the vents are missing, too few, or blocked, the attic runs warmer. The roof vents and the baffles that keep insulation clear of the soffit are a roofer’s or an insulator’s job.

Soffit that lets air in. The intake half of that airflow comes through the soffit under your roof overhang. Soffit can be vented or solid, and vented soffit only helps if the air path behind it is open. A stretch of solid panel, or insulation stuffed against the back of a vented one, starves the attic of air. If your soffit is due for replacement, it is the moment to check which parts of the overhang should be vented; our guide to vented vs solid soffit covers how to tell.

Eavestrough that drains. This is the part we do. A run set to the right slope, with downspouts that are clear and in the right places, does not hold standing water to freeze. It will not stop an ice dam caused by the attic, but it stops the eavestrough from adding to it, and it means the spring melt goes where it should. Where that water lands matters as well: see where your downspouts should drain.

On the roof itself, roofers lay a waterproof membrane under the shingles along the eave, often called eave protection or ice and water shield, so that water pooling behind a dam has a second barrier. Whether yours has it is a question for a roofer.

What should you not do about an ice dam?

A lot of ice dam damage is done by trying to get rid of the ice in a hurry. Avoid these:

• Chipping the ice off with a hammer, axe or shovel. The ice is bonded to the shingles and the eavestrough, and the tool goes through both long before the ice gives.
• Pulling icicles down off the eavestrough. A big icicle is frozen to the run. Yanking it puts the whole weight on the hangers and can tear the eavestrough off the fascia.
• Open flame or a heat gun on the roof. It can scorch shingles and is a fire risk at the roof edge.
• Climbing a ladder onto ice. Ladder feet slip on frozen ground and the roof edge is the worst place to stand on ice. No eavestrough is worth a fall.
• Buying a gutter guard to fix it. Ice can build up in a guard, right at the roof edge, and a guard does nothing about the heat that makes the dam. Our guide on whether leaf guards are worth it goes into why we are not fans.

What is safe: clearing the lower few feet of snow off the roof from the ground with a roof rake, gently, so you are not dragging it hard across the shingles, and staying well clear of power lines. Less snow at the edge means less to melt. If water is already coming inside, call a roofer rather than going up yourself.

Heat cables laid along the eave are sold for this. They can keep a channel open for meltwater, but they treat the ice, not the heat loss causing it, and they need power and care to install safely. Ask whoever installs them how they attach without damaging the shingles or the eavestrough.

When should you call someone, and who?

It depends on where the damage is, so it helps to know whose trade each part is.

Water inside the house. Stains on the ceiling or upper walls, or drips in the attic, mean water is getting under the shingles. That is a roofer first, and then an insulator to deal with the heat loss behind it.

Eavestrough bent, sagging, leaking or pulling away after the thaw. That is us. We look at the whole run, find whether it is a hanger, a section, the slope or the board behind it, and tell you whether it is an eavestrough repair or a replacement.

If the damage is a few sections on otherwise sound eavestrough, a repair is usually the right spend; our guide on whether to repair or replace your eavestrough shows how to tell.

Fascia that is stained, soft or crumbling. Also us. The board usually cannot be replaced with the eavestrough still in place, so the eavestrough comes down, the fascia is replaced, and the run goes back up or is replaced. See how we handle soffit and fascia repair.

The same ice dam, every winter, in the same spot. That is the attic telling you where it loses heat. Fixing the eavestrough will fix the damage, but the dam will come back until the attic is sorted.

If your eavestrough took a beating last winter, ask us to take a look. The inspection and the quote are free, and if the cause is in the attic or the roof, we will say so.

Common questions

Will new eavestrough stop ice dams?

No. New eavestrough that drains properly stops the run from adding to the ice and fixes the damage last winter did, but the dam itself comes from heat in the attic. Replace the eavestrough without dealing with that, and the new run ices up the same way.

Are icicles on my eavestrough a sign of an ice dam?

Not always. A few icicles are normal. A thick ridge of ice along the roof edge with icicles hanging off it, or icicles that build in the same stretch every year, point to heat loss above, or to a run that is holding water in a sag.

Can ice damage seamless eavestrough?

Yes. Ice puts weight on any eavestrough, seamless or sectional, and enough of it can pull a run away from the fascia or bend the front edge. Seamless has no joints along the run, so there are fewer seams for ice to open up. Here is how seamless compares with sectional.

Do you serve my area?

We work in London and the surrounding area, including Ingersoll, St. Thomas, Strathroy-Caradoc, Stratford and Aylmer. If you are nearby but not on that list, call and ask.