Roof and gutter de-icing cables: what they can and cannot do

The job of a de-icing cable

Every Edmonton winter brings the same scene: icicles hanging from gutters, downspouts packed solid and a ridge of ice along the eaves. When a chinook or a sunny afternoon melts snow on the roof, the water runs down to a cold edge, refreezes and has nowhere to go.

Roof and gutter de-icing cable is heating cable laid along the roof edge, in the gutters and down the downspouts. Its job is narrow: keep a channel open so meltwater can drain off the roof instead of backing up under the shingles.

Commercial buildings use the same idea on a larger scale: roof drains, scuppers and internal leaders that freeze and back water up onto a flat roof. Those systems are usually designed with the building's drainage plan and hard-wired to a controller.

It does not melt all the snow on the roof, and it does not stop the heat loss that causes most ice dams in the first place. Knowing that up front avoids disappointment and wasted power.

How a system is laid out

A typical residential layout has three parts:

• Roof edge: cable in a zigzag or triangle pattern above the eave, reaching up past the line of the exterior wall where the roof turns from warm to cold.
• Gutters: a run of cable along the bottom of each gutter so water in it stays liquid.
• Downspouts: cable dropped down inside each downspout to the outlet, so the drain path stays open all the way to the ground.

The cable is held with clips made for the roofing material, never nails or screws through the cable. On metal roofs and in valleys, the layout changes. The manufacturer's installation guide sets spacing and how high the triangles need to go.

The bottom of the downspout matters. If it empties onto a frozen splash pad or into a buried drain that is full of ice, water will back up anyway. Sometimes the fix is to end the downspout above grade or trace part of the drain line.

What it cannot fix

Ice dams start because heat escapes from the house into the attic and warms the roof deck. Snow melts on the warm part of the roof and refreezes at the cold overhang. Cable at the edge keeps a path open, but the melting keeps happening.

If you have heavy ice every year, look at the attic first: air leaks from pot lights and bath fans, thin insulation and poor ventilation. Our guide on ice dams and attic electrical explains how electrical fixtures can be part of the problem.

Control: the difference between useful and wasteful

A lot of roof cable in Edmonton is plugged in each November and left on until April. That wastes power and wears out the cable. Better control options include:

A combined snow and temperature controller only runs the cable when it is cold enough to freeze and there is moisture to melt. For most homes it is the best balance of protection and running cost. A simple air thermostat is a step up from a manual switch.

Where you mount the sensor matters. A snow sensor belongs where it sees real precipitation, clear of overhangs and dryer vents. A gutter-mounted moisture sensor reacts to meltwater in the gutter itself. Some homes use both. A poorly placed sensor is the most common reason a good controller seems not to work.

What drives running cost is cable length, cable output, how many hours it runs, and how well the attic is sealed. Control is the one you can change easily.

Electrical requirements

Roof and gutter cable must be listed for that use, and the circuit needs ground-fault protection under the Canadian Electrical Code. Plug-in kits are made for small areas. Larger or permanent systems are hard-wired on a dedicated circuit with a weatherproof junction box and a controller.

• A dedicated circuit sized for the cable's start-up current in cold weather.
• Ground-fault equipment protection, built into the breaker or the controller.
• Weatherproof connections at the roof, with drip loops and no taped splices.
• A permit for hard-wired work, from the City of Edmonton or your local permit authority.

Older roof cable was often plugged into whatever outdoor outlet was handy, sometimes through an extension cord running up the wall. If that describes your setup, it is worth having it looked at. A cord left outdoors for years, under snow load, is not a safe permanent feed.

Fall checklist for homeowners

Before the first big snowfall, from the ground or a safe ladder position in dry weather:

1. Clear leaves and debris from gutters and downspouts so the cable is not buried.
2. Look for clips that have come loose or cable sagging off the roof edge.
3. Check for cracked or crushed sections where snow slid off or a ladder rested.
4. Press TEST on the GFCI or ground-fault breaker and reset it.
5. Switch on the controller or thermostat and confirm the indicator light works.

If anything looks damaged, or the protection trips, leave it off and book a check. Our roof and gutter de-icing team can inspect, repair or replace cable, and add a better controller to an existing system.

Common questions