What the cables do
The cable is laid in a zigzag along the bottom of the slope, then in the gutter and the downspout. When it heats up, it melts the snow and ice touching it.
The result is a series of grooves in the ice. Water running down the roof follows these grooves, reaches the gutter and leaves through the downspout. The ice between the grooves stays put, and that is normal.
The cable does not replace roof de-icing when an ice dam has already formed and water is getting in.
Their limits
- They treat the symptom. Ice at the roof edge generally comes from heat escaping from the house through the attic. The cable changes nothing about that heat loss. The cause and its remedies, insulation and ventilation, are covered elsewhere on the site.
- They use electricity, all winter long if nobody turns them off.
- They can move the problem. Ice sometimes forms again just above the cables, or lower down where there are none.
- They are held by clips fastened to the roof. Badly installed clips damage shingles or get torn off by sliding snow.
- They age. A cable that no longer heats often goes unnoticed until the ice comes back.
When they make sense
Cables mostly help where the cause is hard to correct. That is often the case with a cathedral ceiling, where there is no attic to insulate further, or a shaded roof valley where ice keeps returning anyway.
Before having cables installed, have the insulation and ventilation checked first. A roof that stays cold over its whole surface generally does not need cables.
Who does what
The electrical connection is an electrician's job, not a roofer's. The electrician decides on the circuit, the outdoor outlet and the protection needed.
Installation on the roof is work at height. It is not a do-it-yourself job on a ladder, and even less so in winter.
When we de-ice a roof that already has cables, we work around them with steam, without hitting or pulling on them. If a cable looks cut, loose or buried in ice, we point it out so you can have it checked by an electrician.
Questions to ask before installation
- Has the cause of the ice been looked for on the attic side?
- Is the cable designed for roofs and for the roofing in place, according to its manufacturer?
- How is it fastened, and what happens to the clips during a future roof replacement?
- How does the cable turn on and off, by hand or with an automatic control?
- How do you check that it still heats, before each winter?
Frequently asked questions
Do heat cables prevent ice dams?
No, heat cables limit the effects of ice dams without preventing them. They keep a path open for water and reduce the risk of it backing up under the roofing. Ice keeps forming as long as the roof loses heat.
Should heat cables stay on all winter?
Not necessarily. Follow the instructions of the manufacturer and the electrician who connected them. A cable is generally useful when there is snow on the roof and water can freeze. It does nothing on a clear roof.
My cables are stuck in ice. What should I do?
Do not pull on them and do not break the ice around them. A stretched or nicked cable can stop heating or become dangerous. Have the ice cleared with steam, then have the cable checked by an electrician.