Technical Elements

During this time of year, NRCA receives many inquiries regarding winter-related issues. Following are some frequently asked questions.

Some of my customers want to remove snow and/or ice dams from their roofs themselves. What is NRCA's position on this issue?

NRCA generally does not recommend homeowners remove ice dams or shovel snow off their roofs because NRCA is concerned with homeowners' safety. Only experienced roofing professionals should perform work on roofs. Additionally, a homeowner may damage roof covering materials and gutters when shoveling and removing ice. Also, homeowners sometimes use "roof rakes"—customized rakes with extra long handles—to remove snow from roofs while standing on the ground. In many cases, a roof rake only will remove snow from a roof system's lowermost sections. The bottom edge of the remaining snow potentially can form a secondary ice dam. Ice-dam protection membranes typically are not installed more than 24 to 36 inches beyond the roof/wall intersection, so water leakage is likely to occur from a secondary ice dam.

What are some solutions to ice damming?

The best time to address ice damming is during a roof system's design and/or construction phase. However, to help homeowners minimize or prevent ice damming, consider the following:

• Proper attic design—Properly ventilating attic spaces and installing additional insulation on attic floors will help keep attic temperatures lower, which should reduce ice damming.
• Ice-dam protection membrane—NRCA recommends the installation of an ice-dam protection membrane on buildings located in areas where the average January temperature is 30 F or lower. An ice-dam protection membrane should be applied starting at the eaves and extend upslope a minimum of 24 inches from the inside face of an exterior wall. If a roof's slope is less than 4-in-12 (18 degrees), the membrane should extend 36 inches. Homeowners should not rely solely on ice-dam protection membranes to prevent water leakage. Attic ventilation, insulation and project-specific detailing for particular climatic conditions also should be considered.
• Gutters—Gutters typically are the first place ice dams form, so eliminating them at roof eaves can minimize the possibility of ice damming. If a gutter system is desired, gutters and downspouts should be thoroughly cleared of debris before winter.
• Electric heat cables—NRCA advises against installing electric heat cables because of the potential drawbacks. NRCA primarily is concerned with the safe operation of cables. Also, the heat from cables can damage roof covering materials. And some electric heat cable systems require exposed fasteners that penetrate roof coverings.

Is it OK to use de-icing salts to melt snow and ice on a roof system?

NRCA does not recommend the use of de-icing salts. De-icing salts are corrosive and may be detrimental to roof covering materials, gutters, downspouts and surrounding vegetation.

At what temperature does it become too cold to install asphalt shingles?

The roofing industry does not provide any specific guidelines regarding a definitive cut-off temperature for installing asphalt shingles, but there are some important issues to keep in mind.

Fiberglass and organic asphalt shingles become brittle at colder temperatures. The Asphalt Roofing Manufacturers Association (ARMA) says shingles become less flexible at temperatures lower than 40 F and more prone to cracking during installation. Cold shingles also may retain the shape of the surface on which they are stacked. Therefore, exercise care when handling and storing shingles in cold weather. Additionally, be careful nailing shingles in lower temperatures because nails may break through the shingles. ARMA recommends shingles be stored indoors before application.

Also, most asphalt shingles have self-sealing adhesive strips, which increase shingles' wind resistances. The adhesive is thermally activated by exposure to the sun or high temperatures, so winter conditions can impede proper adhesion of self-sealing strips. If there is concern, hand-tabbing—manually sealing shingles with asphalt flashing roof cement—is an alternative option.

Joan P. Crowe, AIA, is an NRCA director of technical services.

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