Heat tapes to stop ice dam back-ups & building leaks: This article describes using heat tapes to stop ice dam damage: prevent roof leaks or attic condensation, attic mold in buildings. It describes proper roof ventilation placement, amounts, and other details.

Adding heat tapes along roof edges can melt holes through existing ice dams to prevent water back-up and leaks into the building attic or walls, and heat tapes can prevent new ice dam leaks from occurring. While the proper and reliable repair for roof ice dam problems is the correct installation of ventilation and insulation and perhaps ice and water shield, heat tapes can provide emergency relief when ice dam problems are already present on a building.

Our page top photo shows roof edge heating tapes installed by an owner to attempt to melt channels through ice that may accumulate at the roof eaves in winter. This is an inexpensive band-aid that may be sufficient if ice dam formation on a roof is rare and/or it is difficult to install good under-roof venting. This roof has eaves and a ridge that could have been vented.

Ice Dam Leak Protection: Use of Heat Tapes and De-Icing Cables on Roof Eaves

[Click to enlarge any image]

Article Series Contents

• HEAT TAPES & CABLES for ROOF ICE DAMS
  • HOW DE-ICING CABLES WORK
  • WHERE to PUT DE-ICING CABLE LOCATION
  • SAFETY WARNINGS for ROOF & GUTTER DE-ICING CABLES
  • HEAT TAPES & DE-ICING CABLES on FLAT ROOFS - separate article

These recommendations for use of de icing cables and heat tapes on roofs (and other solutions to ice dams on building roofs) are based on many years of building inspections, on the observation of the locations of moisture, mold, ice dams, condensation stains, and other clues in buildings, and on the correlation of these clues with the roof venting conditions at those properties, and frequent literature review and professional discussion.

We have also measured changes in airflow, temperature, and moisture before and after installing roof venting.

Watch out: for slip and fall hazards if adding heat tapes to a roof in freezing weather. Working from a ladder at any time of the year is dangerous, but risks are multiplied in cold, freezing conditions.

Watch out: also where you are plugging in your heat tapes. Handling wiring in wet conditions risks electrocution. Outdoor outlets are generally GFCI-protected to reduce shock hazards but electrical receptacles high on a building or in building soffits may not contain that protection.

Watch out: improper heat tape installation can not just shock someone, it can cause a fire. "Illinois: Electrical Flaw Suspect in Fire" reported the New York Times in February 2009. The Times reported that experts were focusing on a possible electrical malfunction in a roof ice buildup protection system on the Holy Name Cathedral in Chicago on February 4th. The resulting fire resulted in a blaze that "tore holes in the roof".

In this article we discuss the addition of heat tapes at roof eaves to stop ice dam leak problems. Also see our separate article: Heat tapes, Heat, Insulation prevent Freeze-Up where we describe proper heating tape selection and safe use.

How to Roof De-Icer Cables Work?

Roof de-icing cables melt a channel (above left) through the ice build-up at roof edges or wherever ice is forming and heating cables have been placed. The melted channels permit water that backs up behind the ice (over the warmer roof sections) to run off of the roof rather than backing up under the shingles where it leaks into the building.

Our photograph (above left) shows the typical installation pattern of roof de-icing cables or heat tapes installed on roofs in the Northeastern U.S. The second photo (above right) shows the roof de-icing tapes melting a drip-channel through snow at the roof edge. No ice had formed on this roof, just snowfall, when we took the photo, but in other weather conditions the owner had seen ice build-up along this roof edge.

ROOF VENTING EXTERIOR INSPECTION provides additional photos of clues that indicate a history of ice dam leaks even when the building is being inspected in warm, snow and ice-free weather.

In the photos above the installation uses clips that attach the heating cable to the edges of individual shingle tabs. The installation looks a little sloppy as we can see that the roof de-icing cable has come loose from its shingle clip at the left side of our photo.

The cables might work better at avoiding ice damage to the roof and ice dam leaks to the building interior if they were carried all the way to the edge of the lowest shingle.

Where ice builds up in gutters or eaves troughs (photo at left), additional cabling may be needed in those systems as well.

Typically roof heating cables or de-icing heat tapes are installed along the lower roof eaves in a V-pattern or zig-zag pattern in the area where ice forms. As our page top photo illustrates, when the roof heating cables are operating they melt channels through the ice forming along the roof edge.

Guide to Placing Roof Heating Cables in Roof Trouble Spots

The three most-common places for ice dam formation on roofs are at the roof edges and eaves and in the roof gutter system and in roof valleys (photo at left).

But as we illustrate at HEAT TAPES & DE-ICING CABLES on FLAT ROOFS you may find surprising ice accumulation on flat roofs or around and below any spot on any roof where there is extra heat loss such as is caused by a void in building insulation or an air leak through ceilings into the roof cavity.

All of these are candidates for possible placement of a roof or gutter de-icing cable as a stopgap or easy method to halt leaks caused by ice build-up in these areas.

Some building roofs, by their shape and design, are just difficult to vent and are likely to have snow traps, ice build-up, and ice dam leaks into the interior unless special measures are taken.

Our photograph of heating cables on a roof slope (left) shows a combination of intersecting roof planes and a building sidewall that will naturally trap snow and perhaps lead to ice dam leaks on the building.

When we see a heating tape or de-icer cable on an older home in a location like this one we pose that the owner has already had reason to worry about snow and ice backup and leaks into the building at this location.

Installing the roof heater cables in this trouble spot is an easy, inexpensive, and quick step to take to avoid ongoing ice and leak problems here.

We'd have preferred that the architect avoid creating this problem intersection of roofs and walls. If the design demands creation of a snow and ice trap such as the one we show here, we'd have preferred that the builder install custom-built flashing or at a minimum, carefully fitted ice-and-water-shield membranes throughout the problem area, including running the membrane up the side-wall of the vertical building dormer against which these roofs spill.

Special products are available to move air up along roof valleys and hips, but they are so costly to retrofit to an existing roof that it makes sense to add them when re-roofing rather than while the roof shingles are still in good shape.

For using heat tapes & de-icing cables on flat and low slope roofs see the detailed installation example
at HEAT TAPES & DE-ICING CABLES on FLAT ROOFS

De Icer Cable & Heat Tape Safety Guide from the US CPSC

Most manufacturers of roof or gutter de-icing kits as well as pipe freeze protection kits (heating cables) recommend that the electrical connection for the heat tape be made at a GFCI (Ground Fault Circuit Isolation) electrical receptacle such as we show just above. At below left we illustrate the temperature sensor on an indoor heating cable intended for use on piping.

[Click to enlarge any image.]

This roof or gutter freeze preventing cable is typically used in lengths from 20 ft. to120 ft. and depending on the length of cable used, will draw between 0.83 amps (20 ft.) and 10.0 amps (120 ft). The installation manual will describe in detail how to estimate the number of linear feet of cable you need depending on the roof slope, width of overhang, total roof width gable-to gable, use of cables in gutters and downspouts and other features. Generally I don't want to buy a cable longer than is needed for the application, both for economy and for safety.

The U.S. CPSC has provided safety recommendations for homeowners using heat tapes to help prevent fires. While this advice was originally aimed at indoor use of heating tapes for freeze-proofing piping, this advice is helpful for outdoor de-icer cable use as well.

Some manufacturers of both roof de-icing cables and indoor heat tapes for plumbing produce electrical heat cables that can be crossed over or touch themselves without melting or burning or starting a fire. Be sure to read and follow the instructions on the de icer cable package.

• Replace heat tapes that are older than three years
• Use only heat tapes certified to meet recognized voluntary fire safety standards such as those provided by Underwriters Laboratories (UL), the Canadian Standards Association (CSA), and the Factory Mutual Research Corporation (FMRC).
• Plug the grounded (3-prong) plug into a grounded GFCI (ground-fault circuit interrupter) protected electrical outlet
• Don't cross the heat tape across itself unless the manufacturer says that's acceptable - crossed heat tapes can overheat and start a fire
• Put the heating tape on the surface of the pipe to be protected from freezing, not on top of pipe insulation, and do not cover the heating tape with insulation unless the manufacturer says that's acceptable. Use only non-combustible insulation on pipes where heating tapes are installed (like fiberglass insulation). Foam or vinyl pipe insulation may catch on fire from a faulty heat tape or faulty heat tape installation.
• Protect the sealed end-cap of the heat tape (see our photo above) from damage and water leaks which could cause a short circuit or fire.
• Use heating tape only for the application approved for that particular heating tape, such as for use on piping. Some heat tapes are designed for use in gutters or driveways while others are designed for use on piping or fuel piping.
• Be sure that the heat tape thermostat (if one is provided) is placed where the instructions say. For example some heat tape thermostats should be placed in contact with the pipe, others left hanging in air. (See our photo above)
• Replace any heat tape that is discolored (a sign of overheating), cracked, melted, or damaged in any way.

Watch out: buy the correct kind of heating tape or cable for your application and don't mix up an indoor-use heating cable with an outdoor use unit. The braided cable type indoor heating cable intended for use where pipe freeze protection is needed can be crossed over or touch itself, and is intended to be installed on piping followed by the addition of insulation around the heat-tape-protected piping.

Outdoor heating cables like the kind used to protect against ice build-up in gutters or at the roof edge are weatherproof to permit safe outdoor usage.

Shown at left in the photo below is a roof heating cable intended for outdoor use. While the braided metal heat tape or cable at the right in the photo below is really appealing and can be made to any length needed, this is not the right stuff. The braided metal cable heat tape and its connectors are intended for use only indoors in a dry location and are designed to prevent pipes from freezing.

See HEAT TAPES to AVOID FROZEN PIPES for advice about using de icing cables and heat tapes indoors on plumbing pipes and equipment.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2018-10-18 by (mod) - easy way to test roof heater (de-icer) lines

If you connect heating cables to power they should feel hot or at least quite warm, but

WATCH OUT: your test could be fooled: many roof heating cables used to avoid ice dams include a thermoatatic control that turns the cable on and off. If it's not cold enough, the heater cable won't turn on - it won't get hot .

Some folks have experimented by leaving the cable assembly in the freezer for a time.

There are also continuity and resistance tests that can be made by a VOM or DMM.

On 2018-10-18 by C.J.

Is there an easy way to test roof heater (de-icer) lines before reinstalling in the fall? I laid them out inside (< 60 degrees) and plugged them in but can't feel a difference, can't see a difference using a candy thermometer and can't tell if they melt a groove in an ice cube or if that is just the weight of the heat line. >

On 2018-03-16 by (mod) - when to plug in the tape and when it’s ok to unplug?

Nancy

You can unplug the heat tape when you do not expect further snow cover on the roof.

The tape is plugged into an electrical receptacle that's as close as possible to the point of use, and that's outdoors, and thus is a GFCI protected outlet.

On 2018-03-14 7 by Nancy

I want to avoid ice dams and a high electric bill. Can you tell me when to plug in the tape and when it’s ok to unplug?

On 2017-02-07 by Marg

How long should heat tape be left on?

On 2017-01-30 by (mod) - small soft aluminum heat tape clips don't stay in place very well long term

Bill,

I agree that the small soft aluminum heat tape clips don't stay in place very well long term. I've also seen stainless-steel wire clips and I've seen makeshift clips added to keep the cables in place.

RayChem makes a more durable clip , the RayChem H913 designed to hold heating cables in place. I've seen what looks like the identical product sold as the SRK13 SR/SRP Cable Roof Clips 25 Pack (under $30. U.S.) from King Electric. These clips have a broad perforated base that can be bonded to the surface or between shingles.

On 2017-01-30 by Bill

Are there permanent anchors for zig-zag heat tape installation on an asphalt shingle roof? The small shingle-edge clips are not always dependable, and it's a chore to reinstall them every fall. The constant re-installation tends to wear the edges of the shingles.

On 2016-11-30 by Donna

I had heat cable installed on my garage roof to prevent ice dam in the gutter. It is very noisy. Sounds like a motor spinning. Is this normal?

On 2016-07-13 by (mod) - use of heating tapes near or on vinyl siding or trim

Good question. I don't know, David, and I suspect that the key ruling advice from manufactuers varies depending on the specific heating cable design and purpose.

But watch out: a typical installation instruction page such as from EasyHeat (www.easyheat.com) roof de-icer cables specifically states:

Never install on a flat roof. Never install on combustible materials. Not suitable for use on metal roofs: ...

Vinyl siding is combustible.

You can contact

Easy Heat, 2 Connecticut South Drive 99 Union Street East Granby CT 06026 USA

or

Easy Heat, Elmira ON N3B 3L7 Tel 800/537-4732 Tel 519/669-2444

Or as your heater cable manufacturer may be someone else, check with the manufacturer.

On 2016-07-13 b by David

Is it safe to have the roof heater cables touching vinyl siding?

(Jan 9, 2015) Dee said:
Who do I call to xheck the wires on my roof

Reply:

A roofer who has experience with hooking up ice dam prevnting heating tapes or cables, an electrician, a handyman, a building contractor:

Watch out: accessing a roof edge from a ladder is always risky, especially in winter.

...

Continue reading at ROOF ICE DAM DIAGNOSIS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

DRIVEWAY & WALK DE-ICING SYSTEMS

HEAT TAPES & DE-ICING CABLES on FLAT ROOFS for a successful use of heating tapes to stop an ice dam leak during cold winter weather.

ICE DAM LEAK EMERGENCY REPAIRS

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