Metal Roofs

Scope Images
Metal roofs provide a durable weather-resistant roof cladding
Metal roofs provide a durable weather-resistant roof cladding
Scope

This guide provides an overview of metal roofing with a focus on installation considerations for homes in coastal high-wind areas. Properly select and install metal roofing  to minimize the risk of damage from wind, water intrusion, hail, seismic activity, and wildfires.

Key steps:

  • Enhance roof deck attachment and roof framing attachments, as needed (roof replacement).
  • Seal the roof deck using one of the following three options, per the IBHS Fortified Hurricane and High Wind Standards:
    • install a self-adhered (peel and stick) membrane over the entire roof deck (recommend a #15 felt bond break between membrane and shingles);
    • install a nominal 4-inch wide roof deck flashing tape over all roof sheathing panel seams and cover with #30 felt or equivalent synthetic underlayment;
    • install a two-layer #30 felt underlayment system (recommended best practice).
  • Install drip edges at eaves and rakes.
  • Install metal roof panels and other roofing products that provide uplift resistance equal to or greater than the design uplift pressure for the roof based on the site design wind speed and exposure category, as required by the IBHS Fortified Home Hurricane and High Wind Standards.
  • Install metal roofing in accordance with manufacturer’s installation instructions, all applicable building codes, and selected best practices.
  • Install flashing at roof penetrations and wall-intersections, properly integrated with roofing and wall underpayments and coverings.

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

Description

During a hurricane, tornado, high winds, or hailstorms, metal roofing can be damaged or blown off the roof, exposing the underlayment, flashing, and sheathing as the only protection against rainwater. Exposed sheathing will eventually succumb to water damage. Unsealed joints or penetrations in the roof sheathing or 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.

Wrong – The clips holding these metal roofing panels were set too far from the roof eave (above red line) and the panels lifted in strong winds

Figure 1. The clips holding these metal roofing panels were set too far from the roof eave (above the red line) and the panels lifted in strong winds. (FEMA 2009).

Metal roofing that is selected and installed for high-wind applications is much less likely to be damaged or blown off the roof during a storm.  Impact-resistant roofing is also available to help protect against damage by windborne debris and hail. Metal roofing is also fire resistant.

Building codes require roofing to be rated for the local wind zone. 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, the Virgin Islands, and American Samoa) generally require products and attachments that can withstand greater wind speeds than the rest of the country (see the wind map from the IRC in the Climate tab). A roof replacement is an opportunity to enhance roof deck attachment, roof framing connections, roofing underlayment, and flashing as needed to meet new standards and building codes.

The International Residential Code (IRC) specifies minimum requirements for design wind loads (2018 IRC R301.2.1), metal roofing underlayment (R905.1.1), metal roof shingles (R905.4), and metal roof panels (R905.10) including deck and slope requirements, material standards and thickness, corrosion resistance, and attachment. Local requirements may exceed the IRC requirements or may require specific product approvals.

There are two broad categories of metal roofing types: metal shingles and metal panels.  The metal shingle category includes simulated shakes that resemble wood shakes and simulated tiles that resemble concrete or clay tiles. There are two general types of metal panels: “exposed fastener” panels and “standing seam” panels.  Exposed fastener panels are factory-made, typically 3 feet wide and 8 to 16 feet long, ribbed to provide stiffness, and attached using color-matching, gasketed screws. Exposed fastener panels are usually stiff enough to be installed over spaced wood battens or purlins. Standing seam panels, also known as vertical seam panels, are site made, attached to the roof with concealed fasteners, and highly resistant to wind and wind-driven rain. Standing seam panels are attached to clips that are attached to the roof. Standing seam panels typically must be installed on roof decks with sheathing (i.e., not over wood strapping or battens). Standing seam roofs are custom made and seamed, to lock the panels together, with specialized tools on-site; individual panels, typically 16-inches wide, are normally installed as one long, continuous piece from the roof ridge to the eave.

Metal roofs are durable, low maintenance, and can be repainted.  The most common materials for metal roofing are steel, aluminum, and copper. These materials are either naturally corrosion resistant or made corrosion resistant when manufactured in accordance with building code referenced standards. Manufacturers rate products for impact resistance; some materials resist impact better than other materials, and heavier gauge metal resists damage from hail better than lighter gauge metal. Metal roofing tends to cost more than asphalt shingles, but a metal roof can last up to 50 years or more. Panels are also available with reflective coatings to reduce heat gain during the cooling season.

Metal roofing manufacturers normally provide a report on individual products with specific details on product materials, installation requirements, fire classification, wind uplift resistance, and impact rating.  The report is known as an Evaluation Service Report (ESR) and is available on the ICC Evaluation Service site (icc-es.org).   

The Insurance Institute for Business and Home Safety® (IBHS) Fortified Home program 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™ Hurricane and High Wind Standards provide guidance for making new and existing homes more resilient and durable in hurricane 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; FORTIFIED Gold focuses on tying all components of the structure together. The IBHS FORTIFIED Roof™ program includes guidance on sealed roof decks, flashing, and roofing attachment.

The Fortified Home High Wind Standards require metal panel roofing systems and their attachments to be installed in accordance with manufacturer’s instructions and to provide uplift resistance equal to or greater than the design uplift pressure for the roof based on the design wind speed for Exposure B. The IBHS Fortified Hail Supplement to the IBHS High-Wind Standards requires metal roofing panels to be UL 2218 Class 4 impact-resistant.  Fortified Home standards also require stainless steel fasteners or clips for metal roofs within  3,000 feet of a saltwater coastline.

For areas prone to wildfires, metal roofs 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 have 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). Metal roofs usually require a noncombustible roof deck or fire-resistant underlayment for the roof assembly to qualify as Class A.  An example of a noncombustible roof deck is gypsum panels installed above a wood structural panel deck. Fire-resistance-rated underlayment products are recommended in all wildfire areas and may be required by local jurisdictions.

How to Install Metal Roofing for New Construction:

Step 1: Install the roof deck using fasteners nailed as required to meet current requirements for nail type, size, and spacing.

Step 2: Seal the roof deck using one of the following three options, per the IBHS Fortified Hurricane and High Wind Standards, and in accordance with the product manufacturer installation instructions:

  • Install a self-adhered (peel and stick) membrane over the entire roof deck (recommend a #15 felt bond break between membrane and shingles)
  • Install a nominal 4-inch wide roof deck flashing tape over all roof sheathing panel seams and cover with #30 felt or equivalent synthetic underlayment
  • Install a two-layer #30 felt underlayment system.

Step 3: Install metal drip edge at eaves and rakes. 

Step 4: Install flashing at all roof penetrations and roof-wall intersections.

Step 5: Select and install metal panels for roofing.

  • Install roofing in accordance with manufacturer’s installation instructions, all applicable building codes, and selected best practices.
  • IRC does not permit metal roof shingles to be installed on roof slopes below three units vertical in 12 units horizontal (25 % slope) and minimum slopes for metal roof panels should comply with following provisions:
    • For lapped, nonsoldered-seam metal roofs without applied lap sealant, the minimum slope is three units vertical in 12 units horizontal (25%)
    • For lapped, nonsoldered-seam metal roofs with applied lap sealant, the minimum slope is one-half unit vertical in 12 units horizontal (4%)
    • For standing-seam roof systems, the minimum slope is one-quarter unit vertical in 12 units horizontal (2%)
    • Metal roof shingles are applied to solid, closely fitted roof deck whereas metal roof panels are applied to solid or spaced sheathing.
  • See the manufacturer’s ICC-ES Evaluation Report (ESR) for specific details for product material, installation requirements, fire classification, wind uplift resistance, and impact rating. 
  • For cooling energy savings in hot climates, select metal roofs with a solar reflectance Index (SRI) equal to or greater than 78 for low-slope and 29 for steep-sloped roofs. (ENERGY STAR Cool Roof certified products are recommended.)
  • Fasteners:
    • Use stainless steel fasteners where within 3,000 feet of a saltwater coastline
    • Use galvanized fasteners for steel roofs.
    • Use copper, brass, bronze, copper alloy, or 300-series stainless steel fasteners for copper roofs. Stainless steel fasteners are acceptable for metal roofs.
    •  Don’t underdrive or overdrive the fasteners. The rubber washer in the fastener should seal the metal surface but should not be pressed.
    • Fasteners should not be angled. Take the fasteners off the roof and re-nail if angled.
    • Standing seam panels are typically attached to corrosion resistant clips that are attached to the roof using corrosion resistant fasteners (screws) as specified by the manufacturer.  
  • It is important to lay the panels straight on the eave-to-ridge course. Ensure that the first metal panel is straight; the rest of the panels will follow the layout of the first panel.
  • Install metal roof panels  to avoid rain water puddling or being trapped by seams so that rain water can drain freely into the gutters.
  • Ensure all roofing and flashing is installed shingle-fashion, where the top layer of the panel or flashing laps over the bottom layer to prevent water draining behind the bottom layer.

Step 5: Install flashing

  • Valley flashing should be of corrosion-resistant metal of the same material as the roof and should extend at lease 8 inches from center and have a splash diverter rib 3/4 inch-high at flow line formed as part of the flashing.
  • Pipe flashing should be sealed with tube sealant and attached using adequate screws.
  • Sections of flashing should have an end lap of at least 4 inches.

Step 7: Install eave clips at the eaves.

  • Eave clips for eave closure should have a smooth finish and allow the water to flow into the gutter.

Step 8: Clean the surface of the roof to remove any debris from construction.

Ensuring Success

Roofing should be inspected and installed by a professional roofing contractor to ensure that the roof system provides robust protection from rainwater and ice dams and that proper flashing is in place.

A building permit may be required for a roof replacement. Ask the local building department. For disaster resistance, comply with the roofing requirements defined by IBHS Fortified Home (IBHS Fortified Technical Resources https://fortifiedhome.org/standards/).

For metal roofing, precaution should be taken to avoid damage in the long term due to corrosion and galvanization. Corrosion can be caused by ponding water and debris accumulation. Corrosion-resistant material should be selected for roofing at coastal areas. Proper flashing and drainage plane should be installed to avoid ponding water and the roof should be cleaned after installation to minimize debris accumulation. To avoid galvanization, contractor must not use different metals on the roof- select screws and other metal accessories to match the material of the roofing panel.

Climate

Roofing is more likely to be damaged or lost in hurricane-prone regions and other high-wind areas, leaving flashing and underlayment exposed and more susceptible to wind and water intrusion.  Selection of high-wind and impact-rated metal roofing is required in high-wind and hurricane regions. Proper installation of roofing is even more important in these areas to protect against storm damage.

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 other high-wind zones. The IBHS FORTIFIED Roof™ program includes guidance on sealed roof decks, flashing, and shingle attachment. 

Metal panel roof covering systems are rated by design pressure. Fortified requires that design pressure ratings for metal panel roof cover systems must come from one of the approved certified test reports and/or testing standards listed in the FORTIFIED Home Technical Bulletin: Metal Roof Panel Selection. However, it should be noted that the design pressure ratings are dependent on proper attachment of the metal panel attachment including the type, size, and spacing of fasteners or clips and should comply with those requirements during installation.

International Residential Code 2018 requires an ice barrier to be installed in areas where there has been a history of ice forming along the eaves. The ice barrier should consist of at least two layers of underlayment cemented together or a self-adhering polymer-modified bitumen and should extend from the lowest edges of all roof surfaces to a point not less than 24 inches inside the exterior wall line of the building. If the slope of the roof is greater than 67%, the ice barrier should not be less than 36 inches measured along the slope from the eave edge of the building.

Wind Regions of the United States
Figure 1. Wind Regions of the United States. (International Code Council 2017).

 

Videos
Publication Date
Description
Video discussing wind-resistant roof types and providing recommendations on how to choose the right roof type for your home per FLASH Strong Home guidelines.
CAD

Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

2009, 2012, 20152018, and 2021 International Residential Code

Section R301 Design Criteria. Discusses provisions for constructing buildings and structures to safely support all loads including dead loads, live loads, roof loads, flood loads, snow loads, wind loads, and seismic loads, resulting in a system that provides a complete load path that meets the requirements for the transfer of loads from their point of origin through the load-resisting elements to the foundation.

Section R302 Fire Resistant Construction. Describes fire-resistant construction of building components.

Chapter 9 discusses requirements for roof assemblies.

Section R902 discusses fire classifications including Class A, B, and C roof covering materials and assemblies.

Section R905 Requirements for Roof Coverings.

Section R905.1 provides requirements for underlayments based on wind design.

Section R905.4 discusses provisions for installation of metal roof shingles including material standards, decking, underlayment, flashing, etc.

Section R905.10 discusses provisions for installation of metal roof panels including material standards, decking, underlayment, attachment, etc.

Retrofit: 2015 and 2018 IRC

Section N1107.1.1 Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

 

2009, 2012, 2015, 2018, and 2021 International Wildland-Urban Interface Code (IWUIC)

Section 504 Class 1 Ignition-Resistant Construction

Section 504.2 Roof Assembly. Roofs shall have a roof assembly that complies with a Class A rating when tested in accordance with ASTM E108 or UL 790. For roof assemblies where the profile allows a space between the roof covering and roof deck, the space at the eave ends shall be firestopped to preclude entry of flames or embers, or have one layer of 72-pound (32.4 kg) mineral-surfaced, nonperforated cap sheet complying with ASTM D3909 installed over the combustible roof deck.

Exceptions:

  1. Class A roof assemblies include those with coverings of brick, masonry or an exposed concrete roof deck.
  2. Class A roof assemblies also include ferrous or copper shingles or sheets, metal sheets and shingles, clay or concrete roof tile or slate installed on noncombustible decks or ferrous, copper or metal sheets installed without a roof deck on noncombustible framing.
  3. Class A roof assemblies include minimum 16 oz/sq. ft. (0.0416 kg/m2) copper sheets installed over combustible roof decks.

Note: 2009 and 2012 IWUIC do not mention compliance with ASTM E108 or UL 790 and do not include the list of exceptions.

Section 504.2.1 Roof valleys. Where provided, valley flashings shall be not less than 0.019 inch (0.48 mm) (No. 26 galvanized sheet gage) corrosion-resistant metal installed over a minimum 36-inch-wide (914 mm) underlayment consisting of one layer of 72-pound (32.4 kg) mineral-surfaced, nonperforated cap sheet complying with ASTM D3909 running the full length of the valley.

Section 505 Class 2 Ignition-Resistant Construction

Section 505.2 Roof Assembly. Roofs shall have a roof assembly that complies with not less than a Class A rating when tested in accordance with ASTM E108 or UL 790, or an approved noncombustible roof covering. For roof assemblies where the profile allows a space between the roof covering and roof deck, the space at the eave ends shall be firestopped to preclude entry of flames or embers, or have one layer of cap sheet complying with ASTM D3909 installed over the combustible roof deck. (2009-2018 IWUIC requires a Class B rating rather than Class A rating and only 2015-2021 IWUIC mentions compliance with ASTM E108 and UL 790.)

Section 505.2.1 Roof valleys. Where provided, valley flashings shall be not less than 0.019-inch (0.48 mm) (No. 25 galvanized sheet gage) corrosion-resistant metal installed over a minimum 36-inch-wide (914 mm) underlayment consisting of one layer of 72-pound (32.4 kg) mineral-surfaced, nonperforated cap sheet complying with ASTM D3909 running the full length of the valley.

Section 506 Class 3 Ignition-Resistant Construction

Section 506.2 Roof assembly. Roofs shall have a roof assembly that complies with not less than a Class B rating when tested in accordance with ASTM E108 or UL 790 or an approved noncombustible roof covering. For roof assemblies where the profile allows a space between the roof covering and roof deck, the space at the eave ends shall be firestopped to preclude entry of flames or embers, or have one layer of cap sheet complying with ASTM D3909 installed over the combustible roof deck. (2009-2018 IWUIC requires a Class C rating rather than Class B rating and only 2015-2021 IWUIC mentions compliance with ASTM E108 and UL 790.)

Section 506.2.1 Roof valleys. Where provided, valley flashings shall be not less than 0.019-inch (0.48 mm) (No. 25 galvanized sheet gage) corrosion-resistant metal installed over a minimum 36-inch-wide (914 mm) underlayment consisting of one layer of 72-pound (32.4 kg) mineral-surfaced, nonperforated cap sheet complying with ASTM D3909 running the full length of the valley.

Retrofit: 2009, 2015, 2018, and 2021 IWUIC

Section 507.1 The roof covering on buildings or structures in existence prior to the adoption of this code that are replaced or have 25 percent or more replaced in a 12-month period shall be replaced with a roof covering required for new construction based on the type of ignition-resistant construction specified in accordance with Section 503.

 

IBHS Fortified Home Hurricane Standards

Section 2.2.2.6.3 Metal shingles and panels. Metal panel roofing systems and their attachment must be installed in accordance with the manufacturer’s installation instructions and shall provide uplift resistance equal to or greater than the design uplift pressure for the roof based on the site design wind speed and exposure category. The metal panels must be installed over continuous decking and one of the acceptable sealed roof deck underlayment options (see Description tab or the Fortified standard for details).

IBHS Fortified Home Hail Supplement

“Metal Roof Impact-Resistance Requirements UL 2218 Class 4 … It should be noted that while impact-resistant metal roofs have good impact resistance and are likely to survive impact from most hailstone sizes without functional damage, metal roofs can be vulnerable to aesthetic damage since hail can cause permanent indentations in the roofing panels. Use of metal roofing products with granular coatings may reduce the visibility of small indentations.”

IBHS Fortified Home High Wind Standards

“Metal Panels. Metal Roof Wind Resistance Requirements. Metal panel roofing systems and their attachment must be installed in accordance with the manufacturer’s instructions and must provide uplift resistance equal to or greater than the design uplift pressure for the roof based on a nominal design wind speed (Vasd)= 110 mph (ASCE 7-05), and an ultimate design wind speed (Vult) = 140 mph, (ASCE 7-10) design wind speed for Exposure B. The metal panels must be installed over continuous decking and one of the acceptable sealed roof deck underlayment options.”

IBHS Fortified Home Technical Bulletin Metal Roof Panel Selection

“An essential but often-overlooked fact is that Design Pressure (DP) ratings are dependent on proper attachment of the metal panels to the roof. Therefore, it is vital to understand the panel attachment requirements, such as type, size, and spacing of fasteners or clips, and comply with those requirements when installing the panels. It is important to reiterate that different connection spacings may be required in roof zones 2 and/or 3 than are required in roof zone 1 in order to meet the corresponding design uplift pressures.

Many metal panel manufacturers also provide specific installation details for metal panel attachments at different areas of the roof, for example, ridges, eaves, valleys, gutters, sidewalls, flashings, etc… manufacturer to obtain all installation information.”

This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.

Existing Homes

Retrofit

For a roof replacement:

  • Remove all existing roofing (claddings and underlayment).
  • Replace any rotten or damaged wood sheathing.
  • Inspect and replace any damaged flashing; Where flashing is missing, inspect and replace damaged sheathing and framing.
  • Inspect the roof deck attachment fasteners and re-nail as required to meet current requirements for nail type, size, and spacing.

How to Install Metal Roofing for Existing Roof:

Step 1: Assess the roof decking and fix any area that may show signs of rot or wear. Ensure the underlayment, eave protection, and drip edges are adequately nailed and installed correctly.

Step 2: Install metal panels or shingles following manufacturer’s instruction and instructions for new construction provided in this guide.

Step 3: Integrate the metal roofing with flashings at roof-wall intersections and roof penetrations.

Step 4: Apply sealant between the metal roof and drip edge.

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

References and Resources*
Author(s)
Federal Emergency Management Agency
Organization(s)
FEMA
Publication Date
Description
A Recovery Advisory guide reccomending practices for designing and installing metal roof systems that will enhance wind resistance in high-wind regions (i.e., greater than 90-miles per hour [mph] gust design wind speed).
Author(s)
International Code Council
Organization(s)
ICC
Publication Date
Description
Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Guide describing the requirements by FORTIFIED Home™ for improving the home's resistance in severe thunderstorms, straight-line wind events, and high winds at the outer edges of tornadoes.
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Guide describing the requirements by FORTIFIED Home™ for improving the home's resistance to high wind and hail.
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Guide describing the requirements by FORTIFIED Home™ for improving the home's resistance in severe thunderstorms, straight-line wind events, and high winds at the outer edges of tornadoes.
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Checklist providing selection and installation guidance for residential, non-structural metal roof systems installed over wood roof decks with a roof slope 2:12 or greater to comply with section R905.1 of the 2015 IRC for a FORTIFIED Roof – New Roof Designation.
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Report summarizing the requirements for strenghtening and protecting the roof, openings in the house, and creating a continuous load path to strengthen walls and foundation per the IBHS Fortified Homes Hurricane Standard for New Homes.
Author(s)
Metal Construction Association
Organization(s)
MCA
Publication Date
Description
An installation training manual discussing the installation of metal roofing materials and related accessories, for both new construction and retrofit projects.
*For non-dated media, such as websites, the date listed is the date accessed.
Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

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