Winter

The roof that leaks in January and is dry in July

A leak that only appears in winter, usually along an outside wall, usually within a few feet of the eave, is almost never a hole in the roof. It is water sitting behind ice and going where water goes when it cannot run downhill.

The mechanism, in four steps

1. Heat gets into the attic

   Through recessed lights, the attic hatch, plumbing penetrations, gaps at the top plates, and thin or displaced insulation. In an older house here it is usually all of them at once.

2. Snow on the warm part of the roof melts

   Not from the sun — from underneath. The deck over the heated attic is above freezing while the air is not.

3. The meltwater refreezes over the eave

   The overhang has no heated space beneath it, so it stays at outdoor temperature. Water reaching it freezes, and the ice builds into a ridge along the eave.

4. Water ponds behind the dam and goes backward

   Standing water works its way under the shingle courses, because shingles are laid to shed running water and nothing else. From there it is onto the deck, into the soffit, down the wall, or onto a ceiling.

The icicles everybody photographs are a symptom, not the problem. The problem is the flat ridge of ice behind them and the pond behind that.

Why this metro gets them

Ice dams need a specific combination: snow on the roof, an attic warmer than it should be, and temperatures that cross freezing rather than staying below it. The Ohio Valley delivers the third one relentlessly — winters here are a long series of thaws and refreezes rather than a single deep freeze — and the housing stock supplies the second. Pre-war houses in Hyde Park, Norwood, Clifton, Columbia-Tusculum, Covington and Newport were built with shallow eaves, minimal insulation, no soffit intake and, frequently, finished space up in the roof. Post-war ranches have deeper overhangs and better attics but often have their insulation stuffed into the eave, which blocks the intake exactly where it matters most.

Box gutters and ice are the same problem

On the historic stock the eave is not a hung gutter, it is a wooden trough built into the cornice and lined with metal or membrane. Everything about an ice dam is worse there. The trough is a container, so meltwater that would run off a hung gutter stays put and freezes. Ice expands into every seam and lifts the lining away from the wood. And because the trough sits on top of the wall, a failure drains into the cornice framing and down inside the building rather than onto the ground.

That is why a box gutter that was dry in November leaks in March, and why the box gutter page treats ice as a structural schedule rather than an inconvenience. If you have box gutters, the winter checklist is: outlets clear before the first freeze, and look at the ceiling below the cornice after every thaw.

What actually fixes it

1. Air sealing the attic floor. The single most effective measure, because it removes the heat that starts the whole sequence. Recessed lights, the hatch, plumbing stacks, bath fans and the top plates.
2. Insulation to depth, evenly. Thin patches over an outside wall are where dams start.
3. Intake ventilation at the eaves, with baffles. Cold air along the underside of the deck keeps the roof at outdoor temperature. See attic ventilation.
4. Exhaust matched to the intake. A ridge vent with a properly cut slot.
5. Ice and water shield at the eaves, which is the layer that keeps ponded water off the deck when a dam forms anyway. It is a defense, not a prevention — see what is ice and water shield.
6. Keep the gutters and outlets clear. A blocked trough freezes first and holds the most weight.

What does not fix it

Heat cable

A zigzag of cable at the eave melts a channel through the ice so water has somewhere to go. It is a management measure for a specific problem eave, it costs electricity every winter, and it does nothing about the heat loss causing the dam. Useful occasionally; not a solution.

Bigger gutters

A gutter does not cause an ice dam and a larger one will not stop it. What a gutter full of ice does is add weight to a fascia that may not be up to it.

Gutter guards

No effect on ice dam formation. A guard covered in ice is a guard covered in ice.

A new roof, on its own

New shingles over the same warm attic will grow the same dams. What a replacement does offer is the one moment when ice and water shield can be installed properly at the eaves, and the ventilation corrected while the roof is open.

Raking the snow off, every time

Removing snow from the lower few feet of roof genuinely helps in the moment and is worth doing from the ground with a roof rake. As a strategy it means being home, awake and able-bodied for every snowfall.

If it is happening right now

• Contain the water inside and move anything that matters. Photograph everything before you clean up.
• Relieve a bulging ceiling from below with a small hole and a bucket. A bulge that lets go takes the whole panel down.
• Switch the circuit off if water is anywhere near a light fitting or an electrical box.
• Clear snow from the lower roof if you can do it safely from the ground. Nobody should be on a snow-covered roof.
• Do not go after the ice with tools. Steam removal by somebody equipped for it is the only method that does not damage the roof.
• Book the diagnosis for spring, when the attic can be inspected and the real work — sealing, insulation, ventilation — can be done properly.