Asphalt Shingle Roofs

Description

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Hurricane and High Wind Areas

During a hurricane, tornado, high winds, or hail storm, roof shingles can be damaged or blown off the roof, exposing the underlayment and the sheathing as the only protection against rainwater (Figure 1). Exposed sheathing will eventually succumb to water damage. Unsealed joints or holes in the roof sheathing due to storm damage can allow rainwater to enter the building, causing severe damage, including saturation of insulation and ceiling drywall, potentially leading to collapsed ceilings and extensive damage to interior finishes and household contents.

Figure 1. High winds pulled the asphalt shingles and sheathing panels off this coastal home, although storm shutters protected the windows (Source: Home Innovation Research Labs ).

 

Roof installation and roof replacements are prime opportunities to upgrade shingles and shingle attachments to meet new standards and building codes and to decide if selecting an above-code strategy for an added level of protection is the right choice for the project. A roof replacement is also an opportunity to enhance roof deck attachment, roof framing connections, roofing underlayment, and flashing, as needed.

The Insurance Institute for Business and Home Safety® (IBHS) offers guidance, best practices, and voluntary construction standards and programs for building in disaster-prone areas, including hurricane and high-wind zones. The IBHS FORTIFIED HOME&#; standards are designed to make homes more resilient and durable; guidance is available for new construction and existing homes in hurricane zones and high-wind zones. There are three levels of FORTIFIED Home: FORTIFIED Roof&#; focuses on the roof; FORTIFIED Silver focuses on roof overhangs, opening protection, gable ends, and attached structures; and FORTIFIED Gold focuses on tying all components of the structure together. The IBHS FORTIFIED Roof&#; program includes guidance on sealed roof decks, flashing, and shingle attachment. Note that even where roofing with enhanced wind resistance is not required by building code, roof resiliency can be improved by implementing IBHS recommendations.

Asphalt shingles properly selected and installed for high-wind applications are much less likely to be damaged or blown off the roof during a storm. Building codes require asphalt shingles to be rated for the local wind zone. Impact-resistant shingles are also available to help protect against damage by windborne debris and hail. Lighter-colored asphalt shingles tend to last longer as they absorb less heat than darker shingles and are less likely to be damaged by prolonged heat. ENERGY STAR certifies roofing products through its Cool Roof designation for reflectivity to reduce solar heat gain into the home.

Homes located in coastal high-wind areas, including hurricane-prone regions (defined in the IRC as areas along the Atlantic and Gulf coasts where wind velocity is >115 mph, and Hawaii, Puerto Rico, Guam, Virgin Islands, and American Samoa) generally require enhanced attachment that can withstand greater wind speeds than the rest of the country. Ask the local building department if your house is in a high-wind or hurricane-prone region or if local requirements exceed those of the national code. Also, see the wind map from the International Residential Code (IRC Figure R301.2(5)A), shown on the Climate tab.

Building codes require asphalt shingles, including hip and ridge shingles, to be tested and classified for wind resistance in accordance with ASTM D or D (see Table 1). Codes also specify the type and minimum size of fasteners (nails) and mandate that the number of fasteners is per manufacturer installation instructions but not less than four fasteners per strip shingle. Local jurisdictions may also require specific approval for roofing products (e.g., ridge vents tested and labeled to show resistance to water intrusion) or specific installation enhancements.

Table 1. Shingle Wind Testing Standard for Various Design Wind Speeds. (Source: IBHS Fortified Home ).

ASCE 7-05 Wind Speed (Vasd)

ASCE 7-10/7-16 Wind Speed (Vult)

Shingle Wind Testing Standard/Classification

100 MPH

129 MPH

ASTM D (Class F) or ASTM D
(Class G or H)1

110 MPH

142 MPH

120 MPH

155 MPH

130 MPH

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168 MPH

ASTM D (Class F) or ASTM D
(Class H)1

140 MPH

180 MPH

150 MPH

194 MPH

1. The standard calculations contained in ASTM D assume Exposure Category B or C and a building height of 60 ft or less. Additional calculations are required for conditions outside of these assumptions.

Generally, each shingle strip should be installed with six nails in high-wind areas, and the location of the fasteners on the shingle is also important for a durable installation (see Figure 2 and Figure 3). Use nails, properly driven, instead of staples. Apply dabs or continuous bands of asphalt roof cement beneath shingles along eaves, rakes, hips, and ridges to enhance shingle securement. (This may be required in some jurisdictions.)

Many shingle manufacturers rate their entire product line as Class H or F (per Table 1) for all shingle types, including strip (3-tab), dimensional (architectural/laminate), and premium (luxury) shingles.

Manufacturers now offer shingles that are impact-rated in accordance with UL (Class 1 through 4, with 4 being the highest rating) and known as SBS polymer-modified asphalt shingles. The rubberizing aspects of the SBS polymers also improve granule adhesion, tear strength, nail pull resistance, and cold flexibility. IBHS testing has demonstrated that asphalt shingles fabricated using SBS polymer-modified asphalt consistently perform better than standard shingles. The IBHS Fortified Home Hail Supplement and Impact Resistance Test Protocol requires that asphalt shingles be ranked Good or Excellent for the roof to qualify for program certification. See the IBHS Fortified Home high Wind Standards  and the IBHS Fortified Home Hail Supplement.

Asphalt shingles should only be installed on roof slopes of 2 in 12 or greater. For roof slopes from 2 in 12 up to 4 in 12, a double underlayment application is required.

Figure 2. Locations of Fasteners for Asphalt Shingles in High-Wind Areas (Source: FEMA ).

 

Figure 3. Incorrect location of fasteners in an asphalt roof shingle (Source: FEMA ).

 

Wildfire Areas

For areas prone to wildfires, asphalt shingles are generally considered a fire-resistant roof covering. Roof coverings have fire classifications of Class A, Class B, or Class C or are unclassified. Class A has the highest resistance to fire, and unclassified have the least. Class A, B, and C roofing must be tested in accordance with UL 790 (Fire Tests of Roof Coverings) or ASTM E108 (Standard Test Methods for Fire Tests of Roof Coverings). Most asphalt shingle roofs have a Class A fire rating and do not require a noncombustible roof deck or fire-resistant underlayment; that is, the asphalt shingles provide a &#;stand-alone&#; Class A fire rating. Other Classes A roof materials include fiberglass reinforced asphalt shingles, fiber-cement shingles, galvanized metal underlaid with gypsum, slate, or tiles with bird stopping. Roofs are very susceptible to embers in a wind-driven fire. A simple roof form, such as a hip or straight gable, is best. Complicated roofs with intersecting planes and valleys form dead air pockets and areas where air currents eddy and can trap burning embers (Colorado State Forest Service ). 

How to Install Asphalt Shingles for New Construction:

1. Install the roof deck using fasteners nailed as required to meet current requirements for nail type, size, and spacing.
2.  Seal the seams in the roof sheathing using tape, roof membrane, or synthetic underlayment. If tape, then cover the decking with underlayment (See Roof Deck Sheathing and Sealing and the IBHS Fortified Hurricane Technical Summary, New Construction.
3. Properly flash all roof penetrations and at roof-wall intersections.
4. Install drip edge at eaves and rakes.
5. Select high-wind-rated shingles (see Compliance tab for more detail) and familiarize yourself with the manufacturer&#;s installation instructions. There are three major categories of asphalt shingles - strip shingles, dimensional shingles, and luxury shingles. They vary in aesthetic value, cost, durability (warranty), and installation technique, including laying and nailing patterns. Although all shingles may have some commonality for application, each type will have specific installation features. Different layouts are used for different types of shingles.
6. Install the starter strip at the eave and rake and secure it with nails (See Figures 4 and 5). Use a self-adhered starter strip or embed the strip in roofing cement for sealing (See the guide Roof Edge Protection).

• The starter strip is usually packaged as two pieces per shingle that need to be separated in the middle.
• The self-adhesive seal strip at the starter strip should face up and be positioned toward the eave edge (or toward the rake edge for starter strips at the rake). The adhesive seal strip bonds to the shingle above it, sealing them together and reducing the chance of wind damage and water infiltration.
• The starter strip should overhang ¼ to ¾ inches past the drip edge for drainage.
• The starter strip at the rake should overlap 3 inches with the starter strip at the eave.
• Starter strips should be nailed 2 to 3 inches up from the bottom of the eave.

1. Install the next course of asphalt shingles on top of the starter strip according to the manufacturer&#;s instructions. Follow the same direction as the starter strip for installing shingles. (If the starter strip was installed left to right, install the shingles from left to right.) Generally, six nails are required to attach one strip of shingle to the roof deck. (See the manufacturer&#;s instructions for the type and minimum nails required.)

• One of the common errors in shingle installation is improper nailing. High nails, low nails, overdriven nails, underdriven nails, angled nails, and inadequate nails are all examples of improper nailing. If pneumatic nailing guns are used, test and adjust the pressure until the nails are in line with the surface of the shingle and not underdriven or overdriven.

Figure 4. Roofing nails should be driven straight and flush, not overdriven, underdriven, or angled (Source: FEMA ).

 

8. If the edge of the roof lies on the roof-wall intersection, properly install the step or continuous flashing and integrate it with the underlayment and shingles. See the Step and Kickout Flashing guide for detailed flashing steps.
9. Install ridge cap shingle along the roof ridge. See Figure 5.
10. Integrate shingles with roof penetration flashings while installing the shingles. See Flashing of Penetrations in Existing Roofs for more detail.

Figure 5. Asphalt shingle installation at roof ridges, hips, eaves, and rakes (Source: FEMA ).

 

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