INFORMATION SERIES: Asphalt Roofing Shingles

Asphalt shingles are the most commonly used type of roof covering for pitched roofs. The overlapping design of their installation directs water downward from one shingle to the next to the edge of the roof where usually the gutter system discharges the water to the downspouts. Asphalt shingles, also known as composition shingles-, are so widely used because of their moderate cost, light weight (compared to wood, slate or tile), their durability and ease of installation. In installations, the normal shingles are overlapped to produce a total roofing weight of about 240 pounds per roofing square. The shingles are surfaced on the top side with mineral granules to provide protection from the elements and an element of fire resistance. The shingles do allow moisture to escape from attic areas in vapor form.

Asphalt shingles are available as single shingles or in strips of several shingles and in a variety of colors and patterns. Regular asphalt shingles are designed to have an expected economic life span of 16-20 years. Roofs with southern exposure may experience a shorter life span. The newer, heavier weight shingles can be expected to increase the normal life span by 5 years. The shingles are normally installed over wood sheathing boards after an underlayment is affixed to the sheathing. The sheathing is nailed to the roof framing members. 

Roof drainage systems are needed to control the disposal of water from the roof. Unless the house is designed with large overhangs to dispose of the water, gutters should be installed to prevent damage to exterior walls and foundation as well as water penetration. The gutters, which may be spiked in place or hung along the eave of the roof, carry the water to the downspouts to ground level. Gutters and downspouts are particularly needed in areas of the country having a high annual rainfall and accompanying cold temperatures.

They will reduce erosion and protect steps and walkways from unwanted water (and ice). In the same fashion, they protect shrubs and other foundation plantings.

Gutters can also be made of wood and be built-in as part of the cornice and lined with metal. Such gutters are known as Yankee gutters. They usually rot and leak since they are seldom maintained. Downspouts, which are usually metal, must be large enough to remove water from the gutters satisfactorily. One downspout every 30 feet is desirable.
Downspouts should be piped away from the house. If underground lines are used, be certain to keep them unclogged and flowing. The major cause of gutter failure is clogging due to leaves. twigs and sediment. Regular cleaning of gutters,
especially in spring and fall, is essential. While cleaning, recheck for leaks. Coating of gutter interiors can prolong their lives.

The HouseMaster Technical Staff suggests that the following guidelines be considered if you are to obtain maximum life from your asphalt shingle roof:

1. Keep trees trimmed to prevent scuffing of the roof shingles by branches or damage from falling limbs.

2. Be careful not to puncture the roof covering installing guide wires and television antennas.

3. Promptly replace missing or damaged shingles. Do not walk on the roof. It is dangerous and can damage shingles. Use walk boards, ladders or other suitable protective devices.

4. Check valley areas annually. Look for torn, worn or lifted spots.

5. On the inside, check the underside of the roof for signs of leakage, especially around vent pipes and chimneys. Also watch for any signs of mold build-up or sheathing delamination.

6. Maintain good ventilation in the attic even in winter months. An automatic vent fan is recommended. Poor attic ventilation can cause severe damage to a roof.

7. In areas with heavy snowfall and subfreezing temperatures, be alert for ice dams which form over the gutters on the eaves. They will cause water damage to the interior ceilings and walls.

Eventually all roofs require replacement. If the roof is worn badly in the tabs or just suffering from overall old age, limit ed repairs won't help. When you do plan on reroofing, consider laying the new shingles over the old ones. Most roof framing is designed to withstand the weight of two layers of shingles. The old roofing will provide additional insulation and you can lay the new shingles without exposing the roof
sheathing to the elements. Plus you avoid the labor expense and mess of removing the old covering, which can amount to 40-50% of the cost of the new roof. 

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