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VENTILATION in BUILDINGS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK SEALING PROCEDURE
AIR POLLUTANTS, COMMON INDOOR
AIR SEALING STRATEGIES
ROOF ICE DAM LEAKS
BASEMENT CEILING VAPOR BARRIER
BASEMENT HEAT LOSS
BASEMENT LEAKS, INSPECT FOR
BLOWER DOORS & AIR INFILTRATION
BRICK WALL DRAINAGE WEEP HOLES
CATHEDRAL CEILING VENTILATION
CEILINGS, DROP or SUSPENDED PANEL
COMBUSTION AIR for TIGHT buildings
COOLING LOAD REDUCTION by ROOF VENTS
CONDENSATION on WINDOWS & SKYLIGHTS
DEW POINT CALCULATION for WALLS
FIREPLACES & HEARTHS
FLAT ROOF MOISTURE & CONDENSATION
GREEN BUILDING CONSTRUCTION
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT RECOVERY VENTILATORS
HOT ROOF DESIGNS: Un-Vented Roof Solutions
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSE DOCTOR, how-to be
HUMIDITY LEVEL TARGET
ROOF ICE DAM LEAKS
INDOOR AIR HAZARDS TABLE
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
INSULATION AIR & HEAT LEAKS
INSULATION INSPECTION & IMPROVEMENT
INSULATION R-Values & Properties
LOG HOME GUIDE
MOISTURE CONTROL in BUILDINGS
ODORS GASES SMELLS, DIAGNOSIS & CURE
ROOF VENTILATION SPECIFICATIONS
ROOF ICE DAM LEAKS
SHEATHING, FOIL FACED - VENTS
STAIN DIAGNOSIS on BUILDING INTERIORS
STUCCO WALL METHODS & INSTALLATION
SWEATING (CONDENSATION) on PIPES, TANKS
THERMAL MASS in buildings
THERMAL TRACKING Indicates Heat Loss
VAPOR BARRIERS & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
VENTILATION in BUILDINGS
WIND WASHING INSULATION At EAVES
WINDOWS & DOORS
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.
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
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.
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.
De Icer Cable & Heat Tape Safety Guide from the US CPSC
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.
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).
Also see Heat tapes, Heat, Insulation prevent Freeze-Up for advice about using de icing cables and heat tapes indoors on plumbing pipes and equipment.
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