Asphalt shingles are the most commonly used type of roof covering for pitched roofs on homes. The overlapping design of the installed shingles provides a double layer of protection as the water flows down the roof slope to the roof edge.
Asphalt shingles, also known as composition shingles, are so widely used because of their moderate cost, lightweight (compared to many other roofing products), durability, and ease of installation. Asphalt shingles are surfaced on the top side with mineral granules to provide protection from the elements and a level of fire resistance.
Asphalt shingles are available in a variety of colors, weights, and patterns. Regular weight asphalt shingles generally have an economic life span of 16-20 years; heavyweight shingles are sold as 30-40 year shingles. Roof surfaces with full southern exposure tend to experience a shorter life span.
The installation of an asphalt roof involves more than just the roofing itself. As illustrated, the shingles are normally installed over solid wood or composite sheathing, which is nailed to the roof framing. A water-resistant saturated felt underlayment is typically rolled out over the sheathing before the shingles are applied. In cold climates, a special rubberized membrane is installed along the eave to provide extra protection from ice dams and water backup. Eave or gable edge flashing is also commonly used in many areas.
Flashings are also required at all roof penetrations. Flashings are angled barriers designed to divert water where a roof plane changes (valley) or at the roof surfaces around a roof protrusion (vent pipe, chimney, etc.). Poorly applied flashings open and allow water to penetrate the roof surface. If valley flashings are too narrow, backed-up water can find its way under the roofing materials. Most reported roof leaks are in fact flashing leaks.
Many homes require a roof drainage system to control water run-off from the roof and prevent damage to exterior elements and water seepage into subgrade areas.
In most cases, metal or plastic gutters are hung along the eave of the roof and carry the water to downspouts, which discharge the water at ground level. Some gutters are made of wood or are built-in as part of the eave framing and lined with metal. Built-in or “Yankee” gutters are more often found on older homes and are prone to damage and eventual leakage as they age.
Downspouts, which are made of metal or vinyl, must be large enough to handle all the water collected by the gutters in a reasonable time period. At least one downspout is usually needed for each 25-30 feet of gutter length.
Gutters and downspouts also help reduce erosion along the foundation and protect steps and walkways from unwanted water (and ice) buildup. All downspouts must be piped away from the house foundation to prevent water accumulation and eventual seepage into the foundation. If underground lines are present, be certain to keep them unclogged and flowing.
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