Asphalt Roofing 101

Home Inspector with HouseMaster Home Inspections
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, light weight (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. The major cause of the failure of roof drainage systems is blockage due to leaves, twigs and sediment buildup. Regular cleaning of gutters, especially in spring and fall, is essential. Coating of gutter interiors and sealing of seams may be needed in some cases to prolong their useful life and prevent leakage.

To obtain maximum life from your asphalt shingle roof:

  • Keep trees trimmed to prevent damage to the roof surface from branches or falling limbs.
  • Check the roof surface annually for obvious damage, lifted or worn shingles. Pay particular attention to valley areas and flashings.
  • Have missing or damaged shingles promptly replaced.
  • Periodically check the underside of the roof for signs of leakage or damage, especially around vent pipes and chimneys. Also look for any signs of mildew or mold, which may be associated with roof leakage or ventilation problems.
  • Maintain good ventilation in the attic even in winter months. Poor attic ventilation can cause damage to a roof structure. Additional vents or an automatic vent fan may be required.
  • In areas with heavy snowfall and subfreezing temperatures, be alert for ice dams which form along the eaves. Ice dams can cause water damage to the interior ceilings and walls.

If isolated portions of a roof show some wear, or if storm damage occurs, repairs can normally be accomplished without much difficulty. But regardless of the type of materials used, eventually all roofing will require replacement. If it is badly worn or just suffering from overall old age, limited repairs won't practically extend its service life. When reroofing, it may be possible to lay the new shingles over the old one, which can avoid the labor expense and mess of removing the old covering. Most roof framing is designed to withstand the weight of two layers of shingles. However, actual roofing conditions, roof framing conditions, and local practices and regulations will have a bearing on the method of reroofing.

Remember, these tips are only general guidelines. Since each situation is different, contact a professional if you have questions about a specific issue. More home safety and maintenance information is available online at

This information is provided for general guidance purposes only. Neither DBR Franchising, LLC nor the local HouseMaster® franchise warrants its accuracy and assumes no liability related to its use. Contact the local franchise office and/or qualified specialists for advice pertinent to your specific house or circumstances. © Copyright 2008 DBR. Each HouseMaster franchise is an independently owned and operated business. HouseMaster is a registered trademark of DBR Franchising, LLC.

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Comments (1)

Paul Peck
Peck Drywall and Painting serving Brevard County, Florida - Melbourne, FL
Licensed Drywall and Painting Contractor

Hey Steve. Grat information. Thank you for this post.


Jun 27, 2010 03:20 AM