Restoration Guide: Roof Asphalt Shingles

Editor's Note: This is article 8 of 13 in the Roofs Chapter of the Old House Web's Home Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.

8. Asphalt Shingles

The Basics

When it comes to shingles, it's an asphalt jungle out there.

Cheap and fairly durable, and with a barrage of new products paving the way, asphalt shingles now account for 80 to 85 percent of the residential roofing market, according to the Asphalt Roofing Manufacturing Association (ARMA).

Backing

Asphalt shingles, a common roofing for an old house, have been around since the late 1880s. Originally, they used cotton and wool for backing, and from the early 1940s to the late 1970s, the backing was composed of recycled waste paper and wood fiber.

Since the late 1970s fiberglass has been the dominant backing and accounts for about 82% of the residential market, with organic-backed shingles accounting for the rest. Fiberglass-backed shingles are lighter than organic, but the latter is more flexible and easier to install in cold weather. Fiberglass-backed shingles have a higher fire-resistance rating than organic, Class A versus Class C.

Design

For years the typical asphalt shingle design has been a sheet 36" long and 12" wide, with three tabs. Notches are cut out between each tab to give the illusion of individual shingles. In the mid-1990s, manufacturers began laminating extra layers onto the tabs to give the impression of shakes or slate tiles. These "architectural" shingles are colored to mimic weathered material and to give the impression of three-dimensional roofing instead of the flat appearance of traditional, single-ply asphalt shingles.

A Question of Quality

There now are so many types and styles of asphalt shingles, it is difficult to judge their relative qualities. There is no single standard for manufacturing that one can use to measure quality. In the past, shingle durability was related to weight. Nowadays, shingles are rated by warranty length, such as 20-, 25- or 30-year, but that is just a manufacturer's claim and doesn't mean much because the fine print of the warranties will differ widely on what is covered and to what extent. There is no accelerated-wear test to judge the relative merits of asphalt shingles.

In the 1990s, the Midwest Roofing Contractors Association ran shear strength tests on a number of types of shingles: almost all of the various types of shingles failed the test. The Asphalt Roofing Manufacturers Association (ARMA) has criticized that test, called ASTM D3462. Nonetheless, it has become the standard for shingle strength, and better asphalt shingles now are certified as meeting the D3462 standard. Many shingles sold by discount wholesale and retails stores will sell weaker products that have not been certified ASTM D3462.

Algae growth is a problem for asphalt roofs, especially in hot, humid climates, and some manufacturers have added compounds to their shingles to retard algae growth. While it is too early to determine the long-term success of these products, they appear to work at least in the short term.

Asphalt shingles are problematic in hurricane-prone regions, as most manufacturers don't warrant their product for wind beyond 80 miles an hour (though in reality they may hold up under stronger wind). To reinforce the roof, installers will secure shingles along edges with asphalt roof cement and increase nailing frequency.

Materials and Methods

1. Repairing Asphalt Shingles

Spot repair for asphalt shingles is relatively easy. Holes and cracks can be temporarily repaired with roofing cement, and curled shingles can be glued back snug to the roof. Badly damaged shingles that need to be replaced can be removed by prying them up slightly and hack sawing the nails to remove the shingle. You simply insert the new shingle, nail it and apply roofing cement over the nail heads.

If a significant number of shingles need to be replaced, spot repair likely is futile and you need an entire new roof--delay could lead to extensive water damage and a major home renovation for you.

2. New asphalt-shingle roof

An added benefit of asphalt-shingle roofing: you can potentially apply a new layer of shingles over an old one. You avoid the cost of removing and disposing of the old roof. However, be careful to assess the condition of the old roof. It will be a "foundation" for your new roof. Also, check for degradation in the sheathing and rafters.

You can only shingle over one existing layer, however. A third layer will add too much weight to the roof structure.

And if your underlayment or sheathing shows degradation or warping, or if the old shingles are so curled that the new layer would not lay down smoothly, you must remove the old shingles. Likewise, if the roof shows any sign of sagging, you should remove the roof and evaluate the structural problem.

One thing to keep in mind: until the late 1970s, some manufacturers used asbestos in shingles. In an old house, it is possible asbestos shingles still could be on a roof, under a second layer. The chance is small, but something to keep in mind, if you are ripping up two layers of asphalt shingles as part of a home renovation.

Shingles should be installed between 40 and 85 degrees. Colder than 40 degrees, and the shingles are brittle and hard to cut. Above 85 degrees and the surface is soft enough that it can be scuffed and disfigured.

Shingles have dabs of adhesive under the lower edge that seal to the layer underneath when they warm up. If it is too cold, that seal may not activate--in which case, it woulc require manual sealing.