Ice Dams and Attic Mold in Syracuse: What the Thaw Leaves in the Ceiling

One ice dam, month by month

December. The first heavy bands come through and the pack sets up on the roof. Nothing is wrong yet. A roof carrying snow in Syracuse in December is a roof doing its job.

January. Cold weeks with a warm attic underneath. Anywhere the ceiling leaks heat (a recessed light, the attic hatch, a bath fan duct, the top of an interior wall) becomes a melt spot on the deck above it. Water runs, reaches the eave, freezes. Icicles along the gutter line are the outdoor symptom of an indoor problem.

February. The dam is thick and the pond behind it is permanent. This is the month water gets into the wall. Nobody sees any of it. Insulation at the top of the cavity soaks it up, the top plate stays wet and the inside of an exterior wall becomes a dark, damp, unventilated space held at room temperature.

March and April. The roof clears, the dam disappears and the wall dries from the outside in, very slowly, because a closed cavity has no airflow through it. Somewhere in here a brown ring appears on a bedroom ceiling near the exterior wall. Sometimes the paint simply blisters along the top of the wall itself. The water that caused it left weeks earlier.

Two winters of that in a row and the sheathing along that eave stops looking like wood that simply got damp once. It goes dark, it stays dark and the nail points start to rust from the inside out.

The Syracuse houses that get hit hardest

Story-and-a-half capes are the local specialty for this. Eastwood, Mattydale, North Syracuse and the earlier Liverpool tracts are full of them: an attic floor converted into bedrooms with knee walls down each side. Insulation gets laid across the knee wall floor and stops at the sloped ceiling, so the little triangular space behind the knee wall stays cold, sits open to the eave and lives directly behind the wall your bed is pushed against.

Deep eaves and boxed cornices hold ice well. Foursquares and the larger James Street houses have generous overhangs for exactly that reason. Anywhere a lower roof meets a wall (a porch roof, a rear addition, a dormer cheek) collects snow from above plus the meltwater coming down to it, then holds both against the siding.

Retrofit insulation without ventilation makes everything worse. A pre-war house that got blown-in insulation but never got soffit vents or a ridge vent runs a warmer deck than it should in the shoulder seasons. Bath fans that terminate in the attic instead of through the roof add a steady supply of indoor moisture at precisely the wrong place.

Vaulted ceilings in later additions belong on the list too. A family room built onto a Camillus ranch with a cathedral ceiling has a couple of inches between the drywall and the roof deck, packed with insulation, with no vent channel behind it. Once water finds that assembly there is nowhere for it to dry to. The same is true of any dormer somebody added to a cape to get a third bedroom out of the attic.

The winter habit that ends up in the basement instead

The companion mistake happens at ground level. The driveway gets shoveled, the plow comes through behind it and all of that snow gets piled against the house, because that is where the room is. A bank packed against a foundation wall melts from the warm side first. The water it releases runs straight down the wall to the footing, which is the last place you want a concentrated supply.

The same goes for roof snow. Whatever gets raked or slides off lands at the drip line, which sits directly over the foundation. Move it out. Six feet away from the wall is a different house than up against the block.

Window wells fill with slush and stop draining. A well with a plugged drain becomes a bucket sitting against a basement window for the rest of the winter. A downspout extension buried under the pack quietly dumps at the wall instead of past it, every thaw, all season.

None of this argues for pulling snow off a roof every week. It argues for finding out where heat is getting into the attic in the first place, because the dam is a symptom of a leaky ceiling plane rather than a snow problem. Houses with a well sealed, well vented attic carry the same snow load all winter and never grow one.

What to look at once the roof clears

Go into the attic on a cold morning with a flashlight, before the sun has warmed the deck. Look at the underside of the sheathing along the eaves for dark staining or a gray bloom. Look at the nail points for frost or rust. Look at the insulation for matted, flattened patches where something wet it. A musty smell at the knee wall door is worth taking seriously on its own.

Inside, check the top of the exterior walls in every room under the eaves. Rings, a soft spot, paint that lifted, a nail pop where wet drywall moved, a closet on a north wall that smells different from the room it opens into.

Do not repaint over a ring until you know the cavity behind it is dry. A meter reading taken through the finish costs a fraction of what it costs to open the same wall twice. If the reading is high, the wall gets opened once, deliberately, at a spot somebody chose on purpose.

Check the ceiling under any roof valley while you are looking. Where two planes meet the water concentrates and the ice builds thicker, so the room under a valley is the likeliest place in the house to find a stain. On an Eastwood cape with a front dormer, that is usually a corner of an upstairs bedroom or the top of a stairwell wall.