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Repairing & replacing asphalt shingle roofs

The Old House Web

This story is excerpted from The Rehab Guide: Roofs ,  one in a series of guidebooks produced by the U.S. Department of Housing and Urban Development (HUD) to keep the design and construction industry abreast of innovations and state-of-the-art materials and practices in home rehabilitation.

Parts of this story: Essential Knowledge  ~~ Repairing Existing Shingles ~~ Installing a New Roof ~~ Take it Further -- Suppliers & Other Reading

ESSENTIAL KNOWLEDGE

Asphalt shingles were introduced into the roofing market in the late-1800s as a by-product of making tar and asphalt-impregnated felts for flat roofs. Early shingles contained up to 33 percent cotton or wool fibers derived from rags, hence the term "rag felt."

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From the early 1940s to the late 1970s asphalt shingle mat was comprised of organic cellulose fibers derived from recycled waste paper and/ or wood fiber. Although organic mat is still available, the dominant base material since the late 1970s has been inorganic (fiberglass) mat. According to recent sales information from the Asphalt Roofing Manufacturing Association (ARMA), fiberglass mat shingles comprise approximately 82 percent of the residential asphalt shingle roofing market, and organic mat shingles (still popular in the Midwest and Northeast because they are more flexible and considered easier to install in cold weather) 18 percent.

ARMA estimates that asphalt shingles represent 80 to 85 percent of the total residential roofing market. The fiberglass mat typically used in the asphalt shingle industry is lighter than organic mat. Fiberglass mat doesn't necessarily perform better but does allow shingles to meet Class A fire resistance ratings, while organic mat only meets Class C.

Organic mat is presaturated with asphalt and then coated with a mineral-stabilized material (limestone, slate, flyash, or traprock). Inorganic (fiberglass) mat is coated with mineral-stabilized material but not presaturated. The mineral-stabilized coating fills the voids between individual mats while at the same time providing increased resistance to fire and weather.

The typical asphalt shingle has been for many years a 36 by 12-inch three-tab strip shingle. The cut-outs between the tabs create the illusion of individual shingles.

Within the last five or ten years, "Architectural" or laminated shingles that simulate wood and slate shingles or shakes have become increasingly popular for higher end housing. These shingles are made of two or even three layers laminated into a single unit. The multiple laminate reinforces the impression of individual shingles and the protective granules are toned to simulate weathered material. Dark colored granules are added to create the impression of shadows, thereby enhancing the three-dimensional, "high definition" effect.

Dark colored granules are also added to some three-tab shingles, such as Owens Corning's Prominence(r) series to simulate the appearance of premium shingles.

Other recent developments include the increasing use of larger-sized "metric" shingles, longer "multi-tabbed" shingles, and distinctly-styled, non-rectangular, diamond and hexagonal (scalloped) shingles.

The proliferation of different asphalt roofing shingle types and styles has made the selection of these materials difficult. In the recent past shingles were categorized by weight, such as 235, 240, 280 pounds, etc. The weight was generally related to service life. Currently shingles are classified by warranty duration, such as 20, 25, 30, or 40-year.

There is no direct relationship between base mat thickness, shingle weight, performance, and warranty. Furthermore, asphalt coatings, the type of fillers, mat thickness, and shingle weight vary from one manufacturer to another, making it difficult to estimate relative performance.

Most of the laminated shingles have been on the market for only the past five to ten years, and there is no long-term history of their performance (the Insurance Institute for Property Loss Prevention assumes that the effective life of an average asphalt shingle is 17 years). There is also no applicable American Society for Testing Materials (ASTM) accelerated wear test that is appropriate for asphalt shingles.

Manufacturer warranties are apt to differ in terms of what is warranted (material, labor, or both), against what defect, for what period (pro-rated or not), with what exclusions (rain, hail, and other variables), or whether the warranty is transferrable.

In response to widespread reports of product failure in the early 1990s, the Midwest Roofing Contractors Association (MRCA) ran shear strength tests on a number of shingle types (asphalt fiberglass, asphalt organic, asphalt laminated fiberglass, and asphalt laminated organic shingles) in accordance with Section 8.1.2 of ASTM D3462, "Standard Specification for Asphalt Shingles Made from Glass Felt and Surfaced with Mineral Granules." All but two of the 20-to 25-year warranted three-tab asphalt fiberglass shingles, and all of the 25-and 30-year warranted asphalt laminated fiberglass shingles failed to meet the test.

The ARMA maintains that tensile strength, tensile elongation, and shingle flexibility are better indicators of potential resistance to shingle splitting than tear strength, and is working through ASTM to improve the D3462 standard to more accurately reflect shingle performance. ARMA maintains that some shingles that don't meet D3462 perform adequately.

Most manufacturers currently produce shingles that meet ASTM D3462, and this standard is increasingly referenced by model code agencies. However, some manufacturers, responding to requests for inexpensive products, make "commodity" 20-and 30-year shingles that do not meet this standard. These shingles, of varying quality, are often sold through discount wholesale and retail outlets stores that supply very price sensitive markets.

Until the standards are revised, MRCA and some other industry representatives recommend purchasing organic or fiberglass shingles that are certified as meeting the tear-strength requirements of ASTM D3462. A recent development in asphalt shingles is algae-retardant surfacing. Manufacturers have in the past experimented with zinc granules to retard algae growth, but these sometimes resulted in white patches and uneven staining.

At least one manufacturer, 3M, that provides granules for roofing manufac-turers has developed ceramic-coated granules that release copper ions over a 10-year period to help reduce the darkening of roofs from algae in hot, humid climates. For the additional cost of $150 to $300 per house, 3M claims that roofs will not require as frequent cleaning, which can remove surface granules. It is too early to evaluate the long-term effectiveness of this material, but there are indications that in the short term it helps retard algae discoloration.

If installing asphalt roofs in hurricane-prone regions, it should be noted that manufacturers generally do not warrant their products for wind speeds greater than 80 mph. Asphalt shingles have frequently performed poorly in high winds, and can be a significant source (along with other roofing products) of wind-blown debris. Such performance, manufacturers point out, is frequently attributed to improper application, substrates, or fasteners (staples are not recommended).

The industry and some regional standards (such as the "Blue Sky" guidelines developed by the Town of Southern Shores, North Carolina) recommend doubling up on weight of shingle underlayments, using polymer-modified asphalt underlayment membranes (such as Ice & Water Shield TM or WinterGuard TM ) instead of, or in addition to, roofing felts, and increasing the nailing pattern from 4 to 6 per shingle and the nail size to 1-1 /4-inch #12 nails with 3 /8-inch head diameter.

Shingles at roof boundaries such as rakes, ridges, hips, and valleys should be secured with hand tabbing of an asphaltic roof cement. Existing shingles should be removed prior to reroofing and the existing sheathing inspected for deterioration. Some municipalities, such as Metro Dade County, Florida, have special requirements, such as allowing only shingles that pass 110 mph testing (but which are not typically warranted by manufacturers beyond 80 mph).

Partly in response to cold temperature and high-wind performance requirements, some manufacturers produce shingles derived from recent flat roof technology developments, with different base mat materials and configurations, as well as modified asphalt formulae.

Malarkey Roofing Co. (with distribution largely in the Northwest) offers a shingle that has a base mat of fiberglass and polyester and an SBS rubberized asphalt (modified with styrene-butadiene-styrene) that it claims increases shingle flexibility to resist tearing and cracking under normal as well as low temperatures. Malarkey makes a three-tab and laminated shingle that is warranted against material failure in up to 100 mph winds.

Another manufacturer, IKO, produces a plastic polymer-modified asphalt shingle (atactic polypropylene) with similar enhanced performance claims.

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REPAIR EXISTING ASPHALT SHINGLES

Isolated small holes or cracks in shingles can be temporarily repaired by troweling on plastic roofing cement. Curled shingles can often be cemented back in place. Individual shingles that are badly damaged can be replaced by slipping a pry bar under the damaged shingle, removing the nails, sliding the shingle out, replacing the shingle, and applying roofing cement to the new nail heads and the bottom edge of the new shingle, and the one above.

If a large number of shingles exhibit excessive drying out, curling, loss of protective granules, cracking, or other deterioration, or if there is evidence of significant leaks that are not due to faulty flashing, then a complete shingle replacement is likely to be required.

  • ADVANTAGES: Repairs are easy to make and are cost-effective over small areas.
  • DISADVANTAGES: If large areas need replacement, or if serious leaks develop, postponing replacement may cause damage to the building's structural elements or finishes.

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INSTALL NEW ASPHALT SHINGLES

A critical decision will be whether or not to remove the existing shingles or apply the new shingles over the existing layer.

According to ARMA, in many cases it is not necessary to tear off the old shingles if the roof has only one layer of shingles, is laying flat and the decking is in good condition. In this instance, the existing asphalt shingles can provide a secondary moisture barrier and the cost of removing and disposing of the old shingles will be eliminated.

The existing shingles will probably have to be removed, however, if an inspection of the roof sheathing/ substrate reveals significant rotting or warping of sheathing members, if there is more than one existing layer of asphalt shingles on the roof, if the roof structure shows signs of sagging along the ridge or truss lines, or if the condition of the existing shingles is so rough and distorted that new roof shingles would not lay flat.

If the roof does not look straight and feel solid, it should be inspected for structural adequacy by a professional engineer or architect. The advice of an experienced roofing consultant or contractor can assist in the determination of the appropriate installations. If there is any serious doubt, a complete removal will lead to the most satisfactory application, as it allows a complete assessment of the condition of the existing roof and will provide the base for a level and flat installation. In any case, adequate roof ventilation should be provided (see "Further Reading").

Ideally, asphalt shingles should be installed only when the temperature ranges between 40 F and 85F. At temperatures lower than 40F shingles become brittle, crack easily, and are hard to cut. At ground-level temperatures of 85 F and above, roof temperatures can be in the mid-100s and the granular material is easily disfigured and scuffed by handling and walking on the roof's surface.

In hot climates, roofers usually begin work at day-break and quit early. In colder climates during the winter, the seal tab adhesives may not set up initially, especially on light, reflective roofs.

Seal tabs may also not set up properly on very steep roofs with slopes over 21 on 12. These installations often require additional applications of roofing cement (see "Further Reading" for cold weather and high slope application recommendations).

Application procedures are critical: incorrect nailing above the seal tab line or over-driven nails can lead to product failure. Shingle manufacturers and ARMA recommend against directly applying asphalt shingles on insulation or radiant barrier decks (see Further Reading).

  • ADVANTAGES: Available in a wide range of types, colors, and patterns, asphalt shingles are by far the most popular residential roofing material. Under most conditions asphalt shingles perform satisfactorily. Laminated shingles can dramatically enhance the building's appearance, especially those with higher roof pitches. Can be applied over one layer of flat existing asphalt shingles, but reroofing directly over sheathing is best. Relatively economical material with low first costs, compared to other materials. Easily installed.
  • DISADVANTAGES: Confusing claims and warranties, and the proliferation of material types and specifica-tions, make it difficult to compare and evaluate different manufacturers' products. Competing products are not necessarily equal, and warranties, specifications, and testing data should be carefully examined and compared. Some asphalt shingle products may perform unsatisfactorily, especially in hot, arid climates where thermal shock conditions (high heat with rapid cooling from thunderstorms) occur. Roofs may darken or stain from excessive moisture or humid conditions. Being a product of nonrenewable fossil materials, asphalt shingles are not the best choice from a sustainability standpoint.

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FURTHER READING
  • "Algae Discoloration of Roofs," ARMA Technical Bulletin #217-RR-89.
  • "Blue Sky Construction Guidelines," Town of Southern Shores, NC.
  • "Builder Tips: How to Minimize the Buckling of Asphalt Composition Shingles," APA, the Engineered Wood Association, Form No. K310F/ revised April 1994.
  • Certainteed Shingle Application Manual, Certainteed Corp., P. O. Box 860, Valley Forge, PA 19482, 3rd edition, 1997-98.
  • "Cold Weather Recommendations for Application of Asphalt Roofing Shingles," ARMA Technical Bulletin #225-RR-97.
  • "Direct Application of Asphalt Shingles Over Insulation or Insulated Decks," ARMA Technical Bulletin #211-RR-86.
  • Residential Asphalt Roofing Manual, Asphalt Roofing Manufacturers Association, 1997.
  • Residential Steep-Slope Roofing Materials Guide, National Roofing Contractors Association.
  • "Recommendations for Application of Asphalt Shingles on Steep Slopes and Mansard Construction," ARMA Technical Bulletin #213-RR-87.
  • "Reroofing: Tear-Off vs. Re-Cover," ARMA Technical Bulletin #223-RR-96. "Shingles and Siding: How to Know When You Need Them Costs, Product Tests," Consumer Reports, August 1997, P. O. Box 2015, Yonkers, NY 10703.
  • The Steep Roofing Manual, National Roofing Contractors Association.
  • "Ventilation and Moisture Control for Residential Roofing," ARMA Technical Bulletin #209-RR-86.

PRODUCT INFORMATION

ASPHALT SHINGLES

  • Atlas Roofing Corp., 1775 The Exchange, #160, Atlanta, GA 30339; 770-993-4479.
  • Bird Inc., 1077 Pleasant Street, Norwood, MA 02062; 800-BIRD-INC. BPCO, P. O. Box 3177, Wayne, NJ 07474-3177.
  • Celotex Corp., P. O. Box 31602, Tampa, FL 33631; 800-CELOTEX (phone); 813-873-4080 (fax); www.celotex.com
  • ELK, 14643 Dallas Parkway, Suite 1000, Dallas, TX 75240; 972-851-0400; www.elcor.com
  • GAF Materials Corp., 1361 Alps Road, Wayne, NJ 07470; 800-766-3411; www.gaf.com
  • Georgia-Pacific Corp., 4300 Wildwood Parkway, Suite 300, Atlanta, GA 303TK; 800-839-2588; www.gp.com
  • Globe Building Materials, Inc., 2230 Indianapolis Boulevard, Whiting, IN 46394; 219-473-4500.
  • GS Roofing Products Co., 5525 MacArthur Boulevard, Suite 900, Irving, TX 75038; 972-580-5600; www.gsroof.com
  • Herbert Malarkey Roofing Co., P. O. Box 17217, Portland, OR 97217; 800-545-1191 (phone); 503-283-5405 (fax); www.malarkey-rsg.com
  • IKO Manufacturing, Inc., 120 Hay Road, Wilmington, DE 19809; 302-764-3100.
  • Owens Corning, One Owens Corning Parkway, Toledo, OH 43659; 800-438-7465 (phone); 419-248-7354 (fax); www.owenscorning.com
  • PABCO Roofing Manufacturers, 1718 Thorne Rd., Takoma, WA 98421; 206-272-0374.

ICE AND WATER BARRIERS

  • Ice & Water ShieldTM, W. R. Grace & Co. Construction Products, 62 Whitemore Avenue, Cambridge, MA 02140; 800-472-2391.
  • WinterguardTM, Certainteed Corp., Roofing Products Group, P. O. Box 860, Valley Forge, PA 19482.

ALGAE MITIGATION

  • 3M Algae Block TM , System, 3M Industrial Mineral Products Division, 3M Center 225-2N-07, P. O. Box 33225, St. Paul, MN 55133-3225; 800-447-2914.

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