How an ice dam forms
An ice dam is a ridge of ice along the lower edge of the roof. It forms when the upper part of the roof is warm enough to melt snow, but the overhang past the outside wall stays cold. Meltwater runs down, hits the cold edge and freezes.
Over days and weeks the ridge grows. Water pools behind it and can work its way under the shingles, through the roof deck and into ceilings and walls. Stained drywall in March is often the first sign.
Signs you have an ice dam problem, not just a few icicles:
- A thick, solid ridge of ice along the eave, often with icicles behind the gutter.
- Water stains or peeling paint on top-floor ceilings and exterior walls.
- Frost on roof nails or sheathing when you look into the attic on a cold day.
- Bare patches of roof between snow-covered areas, showing where heat escapes.
Edmonton is a perfect setting. We get long cold spells broken by chinooks and sunny days, and many homes have attics with patchy insulation and a lot of air leaks. A warm attic plus a freeze and thaw cycle is all it takes.
Electrical fixtures are a common leak
Insulation slows heat, but air leaks carry it straight into the attic. A surprising number of those leaks are around electrical work in the top-floor ceiling:
- Pot lights. Older recessed fixtures were often not rated for contact with insulation, so insulation was kept back from them. Many also have open housings that let warm air flow up.
- Bathroom exhaust fans. Fans that dump air into the attic, or ducts that have come apart, push warm, moist air right where you do not want it.
- Ceiling boxes and wire holes. Every light box and every hole drilled through the top plate for a cable is a small leak unless it was sealed.
- Attic hatch. Not electrical, but often the largest single leak in the ceiling.
Moisture rides along with that air. Warm indoor air carries water vapour, and when it hits the cold roof deck it frosts. That frost melts on a mild day and drips onto insulation and ceilings, which can look like a roof leak even when the shingles are fine.
On their own, each leak seems small. Together, in a bungalow with a dozen old pot lights, they can keep the roof deck warm enough to melt snow even when it is far below freezing outside.
Pot lights: what to look for
Recessed lights in an insulated ceiling need to be rated for it. Look for markings on the housing, visible from the attic or after removing the trim, that say the fixture is rated for insulation contact (IC) and airtight.
If your top-floor pot lights are older, an electrician can replace them with IC-rated airtight housings or slim LED wafer fixtures that mount in a sealed box. That usually lets you add insulation over them and cut the leak at the same time. An LED retrofit often pays back through lower lighting energy as well.
Never pile insulation over a recessed light that is not IC-rated. Older incandescent fixtures can overheat and start a fire. Have them replaced first.
Bathroom fans and ducts
A bath fan moves a lot of warm, wet air. If the duct ends in the attic, or has slipped off the fan or the roof hood, that moisture frosts onto the underside of the roof deck. On the next warm day it melts, drips and soaks insulation. It also adds heat that melts snow above.
The fix is an insulated duct, sealed at both ends and sloped so condensation drains out, ending at a proper exterior hood. If the fan is old and noisy, it is a good time to replace it with a quieter unit. A timer or humidity control helps it run long enough to clear the room.
While the electrician is in the attic, they can also seal around ceiling boxes and wire penetrations with fire-rated sealant where appropriate.
Where heat cable fits in
Fixing the leaks is the long-term answer. Roof and gutter heating cable is a useful backup on stubborn spots, such as north-facing eaves, valleys and areas over a heated room with little attic space.
The cable keeps a path open for meltwater to drain. It does not stop the melting. Our guide to roof and gutter de-icing cables covers layout and control.
An energy assessment with a blower door test shows where the attic leaks are. Bring that report to your electrician so electrical fixes target the worst leaks first.
Planning the work
Electrical attic work is usually done in fall or spring, when the attic is not dangerously hot and the roof is not loaded with snow. A typical scope might include:
- Survey top-floor pot lights, fans and ceiling boxes from below and in the attic.
- Replace non-rated pot lights with IC-rated airtight fixtures.
- Reconnect or replace bath fan ducts and add exterior hoods.
- Seal electrical penetrations, then coordinate with the insulation contractor.
- Add or upgrade roof and gutter cable where problem spots remain.
What drives cost: the number of fixtures, attic access and height, whether insulation must be moved and replaced, and how much ceiling repair is needed. Electrical changes need a permit from the City of Edmonton or your local permit authority.
Older homes may also turn up knob-and-tube wiring in the attic. It should not be buried in insulation. If you find it, have a home electrical inspection before any insulation goes in.
Common questions
How do I know if my pot lights are IC-rated?
Look at the label on the housing, which you can usually see after removing the trim ring or from the attic. If there is no label or you are unsure, an electrician can identify the fixture.
Will new LED bulbs in my old pot lights fix the leak?
No. A new bulb lowers heat from the lamp but does nothing about air leaking through the housing. The housing needs to be airtight or replaced.
Can I add insulation over old wiring in the attic?
Modern cable can usually be covered. Knob-and-tube wiring should not be buried in insulation. Have an electrician check first.
Is heat cable enough to stop ice dams?
It helps water drain, but the cause is heat loss into the attic. Sealing and insulating the attic gives the longest-lasting result.
Codes and permit rules change and every building is different. For work on your system, talk to a licensed electrician and your local permit authority.