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Roof 101

Explore an overview of the top 3 predominant residential roof covers in America: asphalt shingles, metal, and tile. Learn the basics of the materials, common installations, and test standards for each.

Roofing Roadmaps: Roof 101 is designed to provide a foundational understanding of each roof cover material in steep-slope roof applications.

Asphalt Shingles

What is Asphalt? What is an Asphalt Shingle?

What is Asphalt?

Asphalt is a petroleum-based product that can either come from natural deposits, such as the Athabasca oil sands in Canada, or can be a refined product. It is characterized by:

  • A complex blend of hydrocarbons
  • Having a sticky, black form
  • A high viscosity (meaning it resists flowing)
Tar is not the same substance as asphalt or bitumen. Tar is a byproduct of coal or wood distillation, not petroleum.

Asphalt is a thermoplastic material that responds to temperature: softens when heated and hardens when cooled. Asphalt is also viscoelastic, which means in certain temperature ranges it can behave like a viscous fluid or an elastic solid.

Asphalt and bitumen are often used interchangeably to refer to both natural and manufactured forms of the substance. Asphalt is almost exclusively an American term, and the substance is usually called bitumen outside the US.

Roofing asphalts are more brittle and harder than most pavement asphalts. To manufacture shingles, a fiberglass mat is saturated with asphalt. Then a limestone filler is used to strengthen the material, but it can also cause the asphalt to become brittle.

What is an Asphalt Shingle?

  • Granules: Coated rocks that protect the fiberglass from damaging UV rays and provide color and aesthetic appeal to the shingle.
  • Asphalt: An oxidized layer for durability and the main water-shedding ingredient in shingles. It also helps to hold the granules in place. 
  • Fiberglass: Center layer of the shingle, often referred to as the base or mat of a shingle, that helps meet the Class A fire rating. 
  • Sealant: A softer asphalt that activates under the heat of the sun to self-seal the shingles together following installation.

Because of the different materials used, conventional asphalt shingles are sometimes referred to as composition shingles. 

 

Impact-Resistant Shingles  

There are two methods to make an asphalt shingle impact resistant:  

  1. Adding a scrim back to reinforce the shingle against hail impacts. 
  2. Using a polymer-modified asphalt (PMA) to give the shingle greater flexibility to resist hail impacts. 

In the early 1980s, polymer-modified asphalt was introduced into asphalt shingle design, but wasn’t embraced. Now, polymer-modified asphalt shingles are becoming the more common impact-resistant shingle.

Types of Asphalt Shingles

3-Tab Shingles

3-tab shingles consist of three tabs separated by a cutout with the sealant strip on the top. These shingles are single layer.

Architectural shingles

Architectural shingles include a double ply overlay with the sealant typically located on the back of the shingle. These shingles are thicker and typically longer than 3-tab shingles.

Other names: dimensional shingles, laminate shingles, composition shingles

Designer shingles generally feature more layers of material for a thicker product and include larger tabs. These products often are designed to look like slate or wood shake.

Other names: premium shingles, luxury shingles

Installation Methods

When asphalt shingles are installed on a roof, underlayment is fastened to the roof deck first, and then the asphalt shingles are installed on top.

Building codes require the use of roofing nails to secure asphalt shingles and are often applied using a pneumatic nailing tool or nail gun for fast installation. Typically, shingles require a minimum of four nails per full-size shingle strip. The specific installation method may vary based on the brand and type of shingle, so the manufacturers’ specifications should be followed and are found on the product wrapper.

Installation Details: 

  • Starter Strip: The starter strip is the first asphalt shingle installed after the drip edge and underlayment. Starter strips are installed at the eaves and the rake edges of a roof and typically have a single strip or dashed line of sealant for the first course, or row, of shingles to adhere to the roof. This detail helps prevent water intrusion and protects against uplift from wind that can occur at the roof edges.
  • Installation Pattern & Alignment: After the first row of singles is applied over the starter strip, shingles in each row are horizontally offset from the previous layer to provide greater protection from the elements, hide seams, and create an appealing look. Each manufacturer prints installation instructions on the product wrapper specific to each product. There are two general installation patterns for asphalt shingles:
    • Pyramid pattern (traditional application) – Shingles are applied diagonally up the roof. For 3-tab shingles, the recommended offset is typically six inches (half the width of a tab). For architectural shingles, the offset varies from four to six inches. 
    • Racking pattern – Each row of shingles is shifted side-to-side (offset varies for shingle type) as they are applied in a column from the eaves up to the ridge. 

Shingles are layered vertically such that the tabs are in contact with the sealant strip on the shingle underneath it. This is a critical part of the installation process that is discussed in the Sealing Process

  • Hips & Ridges: Hip and ridge cap shingles are designed to bend more to cover the seams where two roof faces meet. These shingles are folded horizontally over roof ridges and fastened with two roofing nails on each side, above the sealant strip. Historically, hand-cutting 3-tab shingles to use as hip and ridge shingles was a common practice; however, with the predominance of architectural asphalt shingles in today’s market, hip and ridge cap shingles are widely used.

Pyramid Pattern Installation

FORTIFIED: What’s different? FORTIFIED Roofs nail it down, seal it up, and lock it in. FORTIFIED requires ring shank nails – more of them and in a tighter pattern – to secure the roof deck to the roof structure, a sealed roof deck to keep water out even when the roof cover is damaged, and additional details at the drip edge to protect the edge of the roof. Find the specifics about FORTIFIED Roof at fortifiedhome.org.

Sealing Process

After an asphalt shingle roof is installed, it needs time to seal. The sealant is a temperature-activated, self-sealing adhesive applied during manufacturing. During installation, proper alignment of the sealant strip is critical so the bottom surface of the top shingle can adhere to the top surface of the shingle below.

Risks before sealing: Until shingles are fully sealed, wind and rain pose a risk to the roof. Wind can lift unsealed shingles, and water can seep underneath the shingle.

Optimal Conditions: Manufacturers recommend temperatures between 70°F and 80°F for sealing and warn that temperatures below 40°F may not allow shingles to seal properly. In the warmth of summer, manufacturers say a roof can seal in a little as one to two weeks, but under less-than-optimal conditions, it can take one to two months or more to fully seal.

Test Standards

The following standardized test methods are used to test and label products on the market today for wind and hail performance. These standards evaluate new products and do not account for the effects of weathering, temperature, aging, or similar factors. IBHS is continually researching ways to improve upon these test standards to accurately set expectations for real-world performance.

Standardized test methods are typically developed by trade associations, government agencies, or standard developing organizations. Standards may be updated periodically or on a specific cadence based on new research, new products, or new technology. These standards are often referenced by building codes in an effort to ensure products used in the built environment have a performance expectation. IBHS continually researches ways to improve upon these test standards to more accurately set expectations for real-world performance.

Wind Test Standards

The American Society of Civil Engineers maintains minimum design wind loads and hazard maps, known as ASCE 7, which governs the design and testing of most building components. These criteria are updated every 6 years (e.g., ASCE 7-16 updated in 2016, ASCE 7-22 updated in 2022).

There are two test standards used for wind ratings of asphalt shingles. The wind resistance of asphalt shingles is directly related to the ability of the sealed shingle to resist the force of the wind acting to lift it from the shingle below.

ASTM D3161 (Wind Resistance of Steep-Slope Roofing Products) – Developed in 1972 by the National Institute for Standards and Technology (NIST), ASTM International maintains this test method to measure a shingle’s ability to withstand fan-induced wind speeds.

Test Method: Panels of shingles are placed in front of a fan jet and experience continuous wind at a given speed for two hours. If the shingle sealant fails and the shingles lift, the product fails the test. If the shingles remain sealed, the product passes the test and receives a classification.

There are three classifications:

  • Class A: Tested to 60 mph
  • Class D: Tested to 90 mph
  • Class F: Tested to 110 mph

These wind speeds relate to the wind speed flowing up the roof – not wind loads.

ASTM D7158 (Wind Resistance of Sealed Asphalt Shingles) – Developed in 2005 from wind engineering research, this ASTM International test method assigns a classification to a shingle’s ability to resist uplift forces based on a two-part test.

Two-Part Test Method:

  1. A low-speed 35-mph smooth wind flow test is performed to measure the suction pressure acting to peel the shingles off the roof.
    • Instead of using the wind loads defined in ASCE 7 like other building components, this test is used to determine the wind loads acting on the shingles.
  2. After being sealed under defined conditions, a universal materials testing machine measures the sealant resistance of 10 small shingle samples to mechanical uplift.

The windspeed classification of the shingle is calculated based on the average sealant resistance of the 10 samples in conjunction with the measured pressure coefficients from the low-speed test.

The classifications from ASTM D7158 relate to wind speed zones on the hazard maps in ASCE 7 to show where geographically these products can be installed. The wind speeds corresponding to ASTM D7158 classes have changed over the life of the standard because of calculation changes in ASCE 7. While wind speeds are often listed with the classes, the wind speeds are not directly a result of the test standard.

These calculations result in one of three classifications:

  • Class D
  • Class G
  • Class H
ASTM D7158-05
2005 publication
ASTM D7158-16
2016 revision
Class D 90 mph 115 mph
Class G 120 mph 150 mph
Class H 150 mph 190 mph

Hail Test Standards

Impact-resistant labeled shingle products have passed one of two standardized tests, and are expected to perform better in hailstorms:

UL 2218 (Steel Ball Impact Test) – Created by Underwriters Laboratories (UL), this test method evaluates impact resistance and assigns a classification of Class 1–4 based on the product’s performance against varying sizes of steel balls dropped from a fixed height to replicate the kinetic energy of actual hailstones. After two impacts in the same location, the product passes if no crack is visible on the back of the shingle and therefore is considered impact resistant to that size classification.

Classifications:
Class 1 – 1.25 in.
Class 2 – 1.50 in.
Class 3 – 1.75 in.
Class 4 – 2.00 in.

 

FM 4473 (Ice Ball Impact Test) – FM Approvals developed this test method using pure ice balls for tile roofs in place of dropping a steel ball on the hard tiles, but this test method can also be used for asphalt shingles. Pure frozen water ice balls are shot or propelled at the shingle to achieve the appropriate kinetic energy for hailstones. After two impacts in the same location, the product passes if no crack is visible on the back of the shingle and therefore is considered impact resistant to that size classification.

Classifications:
Class 1 – 1.25 in.
Class 2 – 1.50 in.
Class 3 – 1.75 in.
Class 4 – 2.00 in.

IBHS Impact Resistance Test

IBHS uses lab manufactured hailstones with a density, strength, hardness, mass, kinetic energy, and terminal velocity that mimics natural hail. This test standard goes beyond a pass/fail test to evaluate the range of physical damage modes to the asphalt shingles.

When the hail impacts the test sample, one of three impact modes occurs:

  • Soft Impact: the hail leaves a slushy residue on the surface of the shingle.
  • Hard Shatter Impact: the hail breaks into many fragments.
  • Hard Bounce Impact: the hail remains whole, does not shatter, and does not leave a slushy residue on the test sample assembly.

The damage on the shingle panel is then evaluated for three defined damage modes:

  • Dents/Ridges (Deformation): alterations of the shape of the shingle
  • Granule Loss: loss of one or more granules
  • Tear/Crack/Rupture (Breach): evidence of damage caused by a tear, rupture, or crack

After the damage is assessed, the product receives a Performance Evaluation Rating that is determined from all impacts in the full test sample.

FORTIFIED: What’s different? Shingles rated Good or Excellent in the IBHS Hail Impact Ratings qualify for the FORTIFIED High Wind & Hail Supplement

Interested in the details? Full test standards are available through:

Metal Roofs

Types of Metal Roofs

Metal panel systems are growing in popularity within the residential roofing industry, and while there are a variety of aesthetics and styles of metal panels, the two most common panel types are exposed fastener and concealed fastener. These panels are usually 24 in. to 36 in. wide and long enough to span from the roof eave to the ridge.

  1. Exposed fasteners include 5-V, Rib, and Tile Profile panels. The sides of these panels overlap, so they are considered lapped panels.
  2. Concealed fasteners include Standing Seam and Snap Lock.

Discontinuous metal roof systems—sometimes referred to as metal tiles—include embossed metal shingles and horizontal metal panels like stone-coated metal that overlap like shingles and resemble tile or wood shake profiles. These systems are classified by their horizontal installation pattern and, depending on the style, can offer a high-end designer look.

Metal Materials

Steel is the most common metal roofing material because of its high strength, low weight, and long-term durability. Steel roofing is generally treated with a metallic coating (galvanized or galvalume) on both sides to help prevent corrosion. Additionally, these panels have numerous color options and paint type durability.

  • Tin still exists on some roofs but is not commonly installed today. Tin typically refers to a galvanized steel that may be coated with tin. Aluminum roofing is both lighter than steel and offers increased corrosion resistance which is an important consideration for roofs in marine and coastal environments.

Aluminum roofing varies in thickness which is measured by the gauge of the material; a thicker material has a lower gauge number (e.g., 26 ga. is thicker than 28 ga.).

Known as Natural Metal, both copper and zinc have an aesthetic appeal and offer high corrosion resistance. Natural metal roofing develops a protective layer, or patina.

Installation Variations

When installing a metal roof, the roof deck material (also known as substrate), the metal roof cover material, the mean roof height, the roof pitch, and the geographic location of the roof must be accounted for in installation because these variables determine fastener patterns.

Different code editions allow metal to be installed over different roof slopes or pitches.

  • The minimum slope for exposed fastener or lapped panels can vary. If a sealant is being applied to the overlapping edges (referred to as a lap sealant), the minimum slope is 25% or a 3:12 pitch. If lap sealant is being applied, a minimum 4% slope or 0.5:12 pitch is required.
  • The minimum slope for standing-seam or snap-lock roof systems is a 2% slope or 0.25:12 pitch.

Manufacturers may also have minimum slope requirements listed in their installation instructions. Metal roofs can be installed direct-to-deck or using a grid of wooden battens over the roof deck. Wooden battens allow for air circulation and ventilation for the roof cover.

Test Standards

Standardized test methods are typically developed by trade associations, government agencies, or standard developing organizations. Standards may be updated periodically or on a specific cadence based on new research, new products, or new technology. These standards are often referenced by building codes to ensure products used in the built environment have a performance expectation. IBHS continually researches ways to improve upon these test standards to more accurately set expectations for real-world performance.

Metal roofs are tested as an assembly, from the deck up, and typically require plywood of varying thicknesses for the roof deck. These test standards use the wind loads prescribed in ASCE 7 and consider other factors like roof height, pitch, and exposure category for testing. The result is a design pressure rating for the roof system for different site conditions. The design pressure rating used when installing a metal roof must be appropriate for the geographic location and site conditions of the roof. Because these roofs are tested as a system, it is important to consider the sheathing being used during testing and installation to ensure proper design loads are met.

Wind Test Standards

For wind resistance, metal roof assemblies are tested using UL 580 followed by UL 1897.

UL 580 subjects a 10 ft by 10 ft metal roof assembly to dynamic and static wind loads. For 5 minutes, a constant pressure is applied to test the static wind resistance. Over a 60-minute period, oscillating pressure is applied below the roof cover using an airbag between the deck and the roof covering and applied above by a vacuum in 10-second intervals.

Pressures increase across the three test classifications. The roof assembly must remain intact through an entire Class to pass that Class. Classifications and design pressures (in pounds per square foot):

  • Class 30: maximum static uplift pressure 45 psf, oscillating pressure range of 22 psf to 42 psf.
  • Class 60: maximum static uplift pressure of 75 psf, oscillating pressure range of 44 psf to 83 psf.
  • Class 90: maximum static uplift pressure of 105 psf, oscillating pressure range of 66 psf to 90 psf.

UL 1897 provides uplift resistance data for the roof assembly and evaluates the attachment of the roof covering system to the roof deck. Similar to UL 580, this test method uses either a vacuum above the assembly to pull up on the roof cover or an air bag between the deck and the roof cover to pressurize the roof assembly from below. In this test, the assembly is pressurized until it fails. UL 1897 classifications for uplift resistance are expressed as the maximum load sustained without failure in pounds per square foot (psf).

FORTIFIED Installation
Metal roofs installed to the FORTIFIED standard must have documentation certifying a design pressure rating from UL 580 and UL 1897 from Florida Building Code Product Approval, International Code Council Evaluation Service (ICC-ES) Report, Miami-Dade Notice of Acceptance (NOA), or Texas Department of Insurance (TDI) Product Evaluation.

Hail Test Standards

For hail resistance, metal roofs are tested to UL 2218, the Steel Ball Impact Test.

UL 2218 (Steel Ball Impact Test) – Created by Underwriters Laboratories (UL), this test method evaluates impact resistance and assigns a classification of Class 1–4 based on the product’s performance against varying sizes of steel balls dropped from a fixed height to replicate the kinetic energy of actual hailstones. After two impacts in the same location, the product passes if no crack is visible on the back of the metal panel and therefore is considered impact resistant to that size classification.

Classifications:

  • Class 1 – 1.25 in.
  • Class 2 – 1.50 in.
  • Class 3 – 1.75 in.
  • Class 4 – 2.00 in.

Interested in the details? Full test standards are available through:

Tile Roofs

Types of Tiles

Tiles are classified by their height profiles with three common profiles: low profile, medium profile, and high profile.

  • Low profile tile appears flat with an up to ½-inch rise. Flat tile is often made of clay or concrete; slate is also considered a type of flat tile.
  • Medium profile tile has a height rise to width ratio of up to 1:5. This typically includes double-roll tile, which can be clay or concrete.
  • High profile tile has a vertical height rise to width ratio greater than 1:5, as installed. This typically includes s-shaped tile, or Spanish tile, and cap and pan tile, or barrel tile. S-shaped tiles are shaped as an ‘S’ and create a rippled look across the roof. Barrel tiles are individual curved tiles that look like the side of a barrel. Barrel tile is typically made of clay or concrete.

Concrete tiles are made from sand, cement, and water that are molded under heat and pressure, while clay tiles are baked, molded terra cotta or ceramic.

Installation Variations

Before building code changes in 2002, tile roofs were often installed with adhesive sets including mortar paddies rather than fasteners. This installation style has been phased out with modern code requirements but could be found on older roofing systems.

Before installing a tile roof, the sheathing must be able to support the load of the tile. There are two main installation techniques used in the US:

  • Board and Batten installation adds 2-in. x 2-in. horizontal wood or composite fastening strips called battens to the roof deck, and the tiles are fastened to these battens. Underlayment is installed beneath the battens.
  • Direct to Deck installation fastens the tiles directly to the roof decking, with underlayment installed in between.

In both assembly styles, the tiles are typically fastened with nails or screws to meet modern code requirements.

Test Standards

Standardized test methods are typically developed by trade associations, government agencies, or standard developing organizations. Standards may be updated periodically or on a specific cadence based on new research, new products, or new technology. These standards are often referenced by building codes to ensure products used in the built environment have a performance expectation. IBHS continually researches ways to improve upon these test standards to more accurately set expectations for real-world performance.

Wind Test Standards

ASTM C1568 (Mechanical Uplift Resistance Method) calculates the mechanical uplift resistance capacity of a tile using a small testing apparatus. In this test, a tile attached to a roof framing is placed on an apparatus that gradually applies a load to the tile through a steel bolt with chain linkage that pulls upward on the tile. The load is applied until the tile detaches from its mounting system and the mechanical uplift resistance is calculated.

The resistance calculated in ASTM C1568 must be greater than the wind loads acting on the tile which is calculated using either ASTM C1569 for non-rigid tiles or ASTM C1570 for rigid tiles.

  • ASTM C1569 (Wind Tunnel Test) assesses where the wind acts on non-rigid tiles as determined by section 1504.3.1.2 of the IBC. Tile installed on a small section of roof deck in a wind tunnel is subjected to winds of 70 mph to 130 mph, and the test data is used to calculate pressure coefficients.
  • ASTM C1570 (Air Permeability Test) assesses air permeability for rigid tiles as determined by section 1504.3.1.1 and 1504.3.1.3 of the IBC using an airtight plenum chamber or is assumed to be a standard 0.2 value.

Hail Test Standards

FM 4473 (Ice Ball Impact Test) – FM Approvals developed this test method using pure ice balls for tile roofs in place of dropping a steel ball on the hard tiles. Pure frozen water ice balls are shot or propelled at the tile to achieve the appropriate kinetic energy for hailstones. After two impacts in the same location, the product passes if no crack is visible and therefore is considered impact resistant to that size classification.

Classifications:

  • Class 1 – 1.25 in.
  • Class 2 – 1.50 in.
  • Class 3 – 1.75 in.
  • Class 4 – 2.00 in.

 

Interested in the details? Full test standards are available through:

Content presented in Roof 101 provides a simple overview of roof systems and their test standards to establish a foundational understanding of steep-slope roofs. For specific details, standardized testing procedures and installation instructions should be consulted.