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Roof Heat Cable and Insulation - A Solid Defense Against Ice Dams

Updated: May 23, 2023

With the kids back in school and summer in the rearview, it's time to start thinking about how well your roof is prepared for the arrival of Old Man Winter. You may say, "Hey, I have heat trace cable installed, so I'm all set." And while you're several steps ahead of the game by already having a heat source placed along the edge of your housetop, you're not quite done.

Heat trace cable works to create channels in the ice that naturally forms along the colder roof eaves, which helps prevent the formation of ice dams. Ice dams are pernicious little mountains of ice that develop when the snow on top of the warmer parts of your roof begins to melt. The melted snow then runs down the roof to the edge, where it comes in contact with the much colder eaves and ices up. This icy buildup blocks additional snowmelt from draining off your roof, damaging shingles, soffits, and gutters, and making your housetop vulnerable to costly leaks.

This temperature variation happens when your attic is not insulated well or if it's improperly ventilated. Sometimes both. Heat rises, so as warm air escapes into the attic from your living areas below, the surface temperature of the roof deck naturally increases. The areas not touched by the warm air, typically the eaves and the soffit, stay icy cold.

Installing or adding new insulation to your attic will help keep your entire attic nice and cool and prevent the snow at the top of your roof from melting and refreezing at the edge. Meanwhile, this takes some of the burdens off of your self-regulating heating cable, so it can work more efficiently to prevent the snow and ice from building up along the roof edges and in your gutters after big storms.

It's a win-win.

If you decide to tackle insulating your attic on your own, our experts with ice dam prevention products have some suggestions:

Look Up Your R-Value Climate Zone

Thermal resistance, or R-value, measures the type of insulation's resistance to conductive heat flow. Warmer climates have lower R-values, while cooler climates typically have higher R-values. The higher the R-value, the more effective the insulation will be at reducing heat flow.

According to the Energy Star website, a person in Maine would need R49 to R60 material for uninsulated attic walls. In Florida, however, the attic walls would only use R30 to R49 insulation. The insulation for the attic floor also carries a significantly lower R-value requirement, starting at 13 for the warmest climate zone and topping out between 25 to 30 for the coldest climate zone.

Choose the Best Material for Your Project

There are several types of insulation available, the most popular being blanket or batt, rigid foam boards, and polyurethane spray foam. Each differs from the other in terms of effectiveness and ease of installation.

Blankets or batting is usually the first type of insulation that comes to mind, and it is by far the most common. And, surprisingly, it's not just made out of fiberglass. Fiberglass batting has the lowest R-rating, meaning that you will probably need a couple of layers for maximum efficiency. With facing material, fiberglass is water-resistant, but if moisture gets into the insulation itself, it will become soggy and likely develop mold and mildew growth or rot.

On the plus side, fiberglass is often pre-cut to fit standard-sized ceiling joists and rafters, and it is easy to customize. It's also non-combustible, which makes it a good fire stop. Be sure to wear protective clothing, eyewear, and a mask, as the tiny fiberglass particles can be hazardous to your skin, eyes, and lungs.

Mineral wool batting is a stone-based mineral fiber that contains basalt rock and recycled steel slag. Mineral batting contains more than 70 percent recycled material, making it more eco-friendly than fiberglass and more energy efficient. It's also highly resistant to moisture and fire. The main drawback of mineral batting is that it is 20 percent to 50 percent more expensive than fiberglass, heavier, and somewhat more difficult to work with.

Denim batting is another eco-friendly option that won't require you to wear a hazmat suit, but it's also on the more expensive side, and it requires a separate vapor barrier to ward off moisture. The R-values for mineral and denim batting are 3.3 per inch and 3.5 per inch, respectively, while fiberglass' R-value comes in considerably lower at 2.7 per inch.

Dense, closed-cell foam boards are inexpensive and easy to install because they can be cut to fit tightly between wall studs, ceiling joists, or pretty much anywhere in your attic. They usually come in three main types: Polyurethane, Polystyrene, polyisocyanurate materials, and even some natural options like wood, straw, and cork. The boards' R-values range from 3.8 per inch to 6.5 per inch, depending on what materials it contains. Unfortunately, the sun is a natural enemy to foam boards, and they can deteriorate over time if exposed to UV rays.

Polyurethane spray foam is considered the most effective form of insulation. It seals gaps and cracks against heat flow, lasts the longest, and doesn't deteriorate when exposed to moisture or sunlight. It's also highly energy-efficient, with its closed-cell version carrying one of the highest R-value ratings of 7.1 per inch. The foam is applied as a liquid and quickly hardens into a solid state, sealing everything. The big negative? Spray foam is the priciest insulation and the type most likely to require the help of a professional contractor, as the fumes are toxic and the vapors flammable. Not really DIY-friendly unless you have experience using it.

For more tips on how to ward off ice and snow damage this winter, stay tuned to our blog at

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