Ice dams: why Maryland roofs leak in winter with nothing broken

What is actually happening

Heat escaping from the house warms the roof deck. Snow on the warm upper part of the roof melts, and the meltwater runs down. At the eaves, which overhang unheated space and stay cold, it refreezes. Do that repeatedly and a ridge of ice builds along the eave.

Water then backs up behind that ridge and sits. Shingles shed water running downhill; they are not designed to hold standing water, so it works its way under and into the house. Nothing is torn, nothing is missing, and the roof still leaks.

Why it is a Maryland problem specifically

It needs a freeze-thaw cycle rather than sustained deep cold, which is exactly what Baltimore winters deliver — dozens of cycles between December and March. Places that stay frozen all winter get fewer ice dams than places that thaw and refreeze repeatedly.

The mid-century housing stock across Pikesville, Towson and the county suburbs makes it worse: those attics were frequently built with modest insulation and minimal ventilation by modern standards, which is precisely the condition that warms a roof deck from below.

The fix is not on the roof surface

This is the part that costs people money. Sealant, heat cables and a new layer of shingles all treat the symptom. The cause is heat reaching the roof deck and air not moving under it.

So the real fixes are: air-sealing the ceiling plane so warm air stops leaking into the attic, adequate insulation, and ventilation that actually works — intake at the soffit as well as exhaust at the ridge. A ridge vent with blocked soffits does very little, and blocked soffits are extremely common where insulation has been pushed into the eaves.

What belongs on the roof

Ice-and-water shield at the eaves is the belt-and-braces part, and it is why we run it at eaves, valleys and every penetration rather than only where a code minimum requires it. It does not prevent an ice dam; it stops one turning into a ceiling.

Heat cables are a genuine last resort for a roof geometry that cannot be fixed any other way. They run on electricity every winter forever, which makes them an expensive way to avoid dealing with the attic.

What to do about one right now

Do not climb up and chip at it. People fall, and hacking at ice with a tool is a reliable way to damage shingles and flashing under the ice.

Clear snow from the lower few feet of roof with a roof rake from the ground if you can do it safely, contain any water inside, and photograph everything. Then deal with the attic before next winter rather than waiting for a repeat.