Every January or February, Rochester gets its warm stretch — a few days above freezing, snow drips off the roof, then re-freezes overnight. Lake-effect loads the roof fast, and Monroe County's mid-winter thaw-refreeze cycle gives all that snow somewhere to go — until it hits the cold overhang and builds into a wall of ice.
The dam itself isn't the problem. It's what follows: water backing up under the shingles, past the underlayment, and eventually appearing as a ceiling stain or wet drywall. By the time you see it inside, infiltration has usually been going on for weeks.
What's actually causing the dam
Heat escapes through your ceiling into the attic. The attic warms up. That warmth transfers through the roof deck and melts the snow on the upper roof. Meltwater runs toward the eaves — but the eaves are cold, because they extend past the heated space below. The water re-freezes there and stacks up. Each thaw-refreeze cycle adds another layer.
Rochester homes get hit harder than most because of the housing stock. A large share of homes in Irondequoit, Brighton, Gates, and the city itself were built between 1920 and 1960 — colonials and capes with finished or partially finished upper floors. Those spaces are notoriously leaky: knee walls with open cavities, attic bypasses at light fixtures and partition top plates, plumbing chases running straight into the cold attic. Homes with knob-and-tube wiring often have bare joist bays — dense insulation around live K&T was a fire risk, so it was left out. The result is an attic that's substantially warmer than it should be, even in deep winter.
Why raking and heat cables are band-aids
Roof raking clears snow before it melts and refreezes. On a steep colonial after a 20-inch lake-effect event, that means you're out every few days, and aggressive technique risks damaging shingles. It doesn't touch the heat loss.
Heat cables keep the eave zone warm enough that meltwater doesn't re-freeze. They work when installed correctly, but they add to your electric bill every winter, require seasonal management, and if a run is too short or the cable fails, the dam comes back. You're heating the outside of your house to fix a problem caused by heating the inside too much.
Neither is wrong as a one-winter stopgap. Both are the wrong permanent answer.
The real fix: air sealing, insulation, ventilation
Air sealing first. This is the step most homeowners skip, and it matters most. Bulk air movement carries heat into the attic far more efficiently than conduction through ceiling drywall. Every electrical box, top plate gap, recessed light, and plumbing penetration is a bypass. Those need to be sealed with foam or caulk from the attic side before any insulation goes in.
In an older Rochester colonial with finished upper floors, air sealing often takes as long as the insulation itself. Knee wall cavities are especially bad — they connect directly to cold attic space, and if they're not blocked and sealed, you're heating open attic all winter.
Insulation. New York code targets R-49 in attic floors for new construction. Most older Rochester homes are sitting at R-11 or R-19 — original construction plus one blown-in upgrade. Getting close to R-49 with blown cellulose or fiberglass in the attic floor reduces the heat available to melt snow in the first place.
Ventilation. Soffit and ridge vents keep attic temperature close to outside air. But ventilation only works if airflow can actually move from soffit to ridge — which requires intact baffles. A common mistake is adding blown insulation that buries the baffles, or starting a job in a house where working baffles were never installed. Baffles need to be in place before the first bag goes in.
What it costs in 2026
Air sealing and insulation for a typical Rochester colonial — 1,400 to 1,800 square feet of attic floor — runs roughly $2,800 to $5,500, depending on how much air sealing is needed, attic accessibility, and whether baffles need work. Capes and homes with knee walls and awkward access run toward the high end. Larger homes or those untouched since original construction can run higher.
That range doesn't include water damage remediation or roof repairs if shingles or underlayment are already compromised.
RG&E and NYSEG offer rebates through the NYS Clean Heat program — typically $300–$800 depending on what's installed. A NYSERDA energy audit (often low or no cost for qualifying homes) will identify exactly where the heat is escaping before anyone picks up a caulk gun.
The mistake that makes it worse
Don't add insulation without air sealing first. Fluffy insulation slows conduction — it doesn't stop air movement. If bypasses are still open, adding R-value can shift where the dam forms rather than eliminate it. And blown insulation that buries soffit baffles removes the ventilation that keeps the roof cold. Both mistakes are easy to make when a job is quoted on insulation depth alone.
Where to start
Pull the attic hatch and look toward the eaves with a flashlight. Daylight around ceiling fixtures, thin insulation near the exterior walls, or open penetrations around pipes — any of those tell you something. A contractor who does attic work can walk that space with you in 20 minutes and tell you where the heat is going.
That's worth doing before next January.