Asphalt Shingle Burn Out


Have you ever wondered why hip and ridge asphalt shingles burnout faster along the ridge of the roof than shingles made from the same material on the rest of the roof? The explanation is less obvious than you might think. The asphalt shingles at the roofs’ peak, its ridge line, are being actively destroyed, even during cold winter months, from heat and moisture build-up inside an un-ventilated or poorly vented attic.

As we all know, heat rises. In this case, to the highest point of the attic, right below the ridge line. And it is here that the heat attempts to escape particularly in today’s more tightly constructed homes. The attic in earlier architectural styles was draftier and less energy-efficient than now. Unlike summer’s hot sun, winter provides a different source of destructive heat. Heat from the homes interior rises into the attic, taking with it water vapor, the unnoticeable consequence of such everyday water-related activities as bathing, washing dishes or doing the laundry.

When an inadequately ventilated attic allows this warm, moist air to accumulate, deterioration of asphalt shingles and even of wooden roof structures is the inevitable result. If winters’ less obvious destructive effects are then added to pre-existing burned-out asphalt shingles along the ridge line, your customer can expect either a long, cold winter or higher heating bills than necessary.

Here’s why. After warm, moist air rises into the attic, it cools, releasing its moisture as condensation, which settles into attic insulation. It doesn’t take much moisture to impair the efficiency of attic insulation. In fact, with only a 1% moisture content, insulation loses 36% of its R-value. During winter decreased R-value means increased heat loss from the home. Because the function of attic insulation in winter months is to help keep the homes’ interior warm and comfortable, heat that escapes through insulation is gone forever. Attracted to the cooler roof sheathing and then to the even colder outside air, heat never re-enters the homes’ interior… a chilly prediction for the owners of unventilated or inadequately vented attics.

High heat, whether from outside or inside, will bake the oils right out of petroleum-based asphalt shingles, shortening the warranty period of products intended to last many years longer than they actually do. There’s no way to prevent exposure to the natural forces of sun, wind, rain or snow but you can vastly reduce premature aging of asphalt shingles by providing good attic ventilation on your customers roof, whether new construction or retrofit.

According to university studies, ventilation is most efficient at the ridgeline where heat normally collects. Old-fashioned turbine vents, for instance, are not only less efficient because of where they’re installed but suffer from homeowner dissatisfaction as well. Owners of turbine vented roofs often regard their whirlybirds as necessary evils, but also complain of the noise, leakage and stark unattractiveness associated with using them. Many people, though, including a number of roofing contractors, still don’t realize how much damage attic heat can inflict on an asphalt shingle roof, a fact that has not been lost on regulatory agencies and corporate executives. This is why the Uniform Building Code requires adequate attic ventilation and so do the warranties of every manufacturer of asphalt shingles. In other words, if you install an asphalt shingle roof without the question of attic ventilation being asked or answered you may as well throw out the manufacturer’s warranty along with the shingle wrappers.

In the long run, a cooler, drier attic helps preserve the life of asphalt shingle roofs but what about short term benefits? Of these, the most important is customer comfort. Not only is venting through the ridge the natural way to ventilate the attic, it is also the most cost-effective. Your customer’s home stays warmer during the winter so heaters and furnaces aren’t turned on as soon in the day or left on for as long, resulting in lower utility bills. But what about curb appeal. Sales figures confirm the popularity of texture and dimensionality among homeowners who select designer premium shingle roofs, a feature no less sought-after on the hips and ridges of the roof. But since none of the dimensional hip and ridge shingles also vent the attic space, they’re especially vulnerable to early burnout.

To satisfy the attic ventilation requirements set by the UBC, your customer’s roof should be installed in accordance with a ratio of one foot net free ventilation for every 150 feet of attic space. For example, a single story 2,500 square foot house with 130 feet of ridge would need 16 square feet of net free ventilation… the equivalent of 20 turbine vents or 128 feet of through-the-ridge venting.