If the covering is over seventeen years old, extended life for the shingles should not be anticipated. Even though the shingles might look all right (lying flat with no noticeable loss of granules or erosion), they are becoming brittle and vulnerable to wind damage. Also, these shingles will be more vulnerable to damage from someone walking on the roof when cleaning the gutters, installing a TV dish antenna, and so on. Often, these shingles will show signs of aging such as curling, cupping, cracking, and pitting. (See FIG. 2-5.) Such shingles are vulnerable to damage and will deteriorate rapidly. An exact estimate of the usable years or months remaining for the shingles is difficult. Some people do not replace an aging roof until there is a leakage problem. Others will replace it before any leakage occurs thus avoiding the cosmetic damage caused by leakage. The life span of an aging roof can be extended by patching and coating exposed cracks and eroded areas. However, even if you see no signs of leakage, the shingles on a roof that can take a second layer should be replaced before they become brittle, curl excessively, crack, and chip, as shown in FIG. 2-6. Because of the physical condition of these shingles, the surface of a second layer of shingles will be uneven, lumpy and aesthetically unattractive. In this case, for a nice even appearance the old shingles need to be stripped off the roof deck before the new shingles are installed. If more than approximately one-third of the roof shingles show signs of advanced aging, I recommend reroofing. At this point, attempts to extend the life of the shingles are usually not economically justifiable.
Wood shingles and shakes
In many parts of the country, wood shingles and wood shakes are used as a roof covering. The basic differences between the two are appearance and thickness. During the manufacturing process, shingles are sawed; shakes are split. Consequently, wood shingles have a relatively smooth surface, and shakes have a textured surface.
Because of the need for resistance to decay, most wood shingles and shakes (hereafter referred to as shingles) are made from cedar. They are also made from redwood and southern cypress. The shingles, although resistant to decay, are not immune to decay and will rot after prolonged exposure to moisture. (Rotproducing fungi are discussed in chapter 8.) The projected life expectancy for a wood-shingle roof is twenty-five to thirty years. As a wood-shingle roof ages, the shingles dry, crack, curl, and rot. As you walk around the house looking at the roof, be aware of aging shingles. Rotting shingles should be replaced. If you notice loose, damaged, or missing sections, repair is needed, even if you see no signs of water leakage. When approximately one-third of the shingles on a slope show signs of excessive aging (rotting, chipped, cracked, loose, missing, or curling), all the shingles on that slope should be replaced.
On the northern slope or on portions of the roof that are usually shaded, you might see moss growing in clusters between the joints of the shingles. It should be removed. The moss functions like a wick; the root system provides a direct path for water entry. In addition, as the moss cluster builds up, it might lift the shingles slightly, making them more vulnerable to water penetration, particularly during a driving rain.
Wood shingles are spaced between 1⁄8 and 1⁄4 inch apart to allow for swelling during damp weather. Because of this space and the irregularities of some of the shingles (due to thickness and texture), daylight might be visible through portions of the roof from the attic. If during your inspection of the attic you see daylight through a wood-shingle roof, don’t think that roof maintenance is necessary. If daylight is visible through the roof by means of an indirect path, maintenance is not required. On the other hand, if daylight is visible via a direct path, such as a crack, some maintenance is needed. Depending on the pitch of the roof, the shingles are two-, three-, or four-ply and are installed so that the joints between the shingles for the various plies do not line up. When daylight is visible via a direct path, cracks in the shingles line up with the joints. In this case, water can penetrate the roof, and maintenance is needed.
Asbestos-cement shingles, currently called mineral-fiber shingles, were manufactured by combining asbestos fibers with Portland cement under high pressure. Although the shingles are no longer manufactured, they can be found on many homes. The shingles possess properties that make them highly suitable for exterior use. They are immune to rot, unaffected by exposure to salt air, and fireproof. One drawback is that they are weak in their resistance to impact and thus are vulnerable to cracking and chipping.
As you walk around the exterior of the building during the roof inspection, look for cracked, loose, chipped, and missing shingles. Note on your worksheet the areas that will require maintenance. Although asbestos-cement shingles individually last many years, an asbestos-cement-shingle roof should not be considered maintenance-free, and periodic repairs should be anticipated. Occasionally, as with a wood-shingle roof, clusters of moss might be found on the northern slope or slopes shaded by trees. If you see this condition, note it on your worksheet. The moss is a potential problem and should be removed.