When designing and installing metal roofs, the stakes are high in hurricane- and tornado-prone areas.

The eastern seaboard and Gulf States from upper Maine all the way down to Texas are contending with a significant increase in the frequency and intensity of hurricanes. And tornadoes are pounding the Midwest and South with alarming regularity.

In 2017 alone, damage from hurricanes were off the charts. Texas bore the brunt of Hurricane Harvey which caused a total of $125 billion in damages. Hurricane Maria hit the Caribbean in September with a $91.6 billion price tag on the heels of Hurricane Irma, which ravaged through the Caribbean and Florida earlier that month causing $77.5 billion in damages, according to the U.S. National Hurricane Center.

Just last year, the U.S. documented a record of seven tropical cyclones and 13 severe storms.

Causing death, injury, and unprecedented property damage, the 2020 billion-dollar disaster report from the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information documents an astounding $1.3 trillion in damages from storms and cyclones since 1980.

For buildings, the first line of defense against these intense forces of nature is the roofing system.

“Because roof covering damage has historically been the most frequent and costly type of wind damage, special attention needs to be given to roof system design,” said Tom Smith, AIA, TLSmith Consulting in the National Institute of Building Sciences Whole Building Design Guide’s (WBDG) “Wind Safety of the Building Envelope.”

From the assorted materials and systems available on the market, high-quality metal roofing is arguably one of the best choices for protection from high winds.

Says the Metal Roofing Alliance, “Metal roofing is in high demand in hurricane-prone regions, due to its exceptionally long-lasting durability and protection against heavy rain, hailstones, and hurricane force winds.”

With larger interlocking panels, and fewer seams and overlaps than other roofing systems, there is less opportunity for the wind to penetrate. In the event that some wind manages to get in between the metal covering and the underlayment, metal’s ability to breathe and expand enables it to endure a high level of wind pressure. Consequently, many metal roofs are rated up to 150 miles per hour—the equivalent of a major Category 4 hurricane and an F2 tornado.

“Out of all the roofing types that are out there, you have got the best chance of survival with a properly installed metal roof,” stated Jim Bush, Metal Construction Association Chairman (MCA) and a member of the Roofing Industry Committee on Weather Issues (RICOWI) wind investigation teams.

Photos courtesy of ATAS International

Underwriters Laboratories (UL) 580 tests and assigns a category based upon the roof deck and coverings’ level of uplift resistance.

Installation and Testing Standards

While high-quality metal roofing systems have been engineered to deliver enhanced durability and longevity, their performance is ultimately dependent on professional installation by roofing experts who are familiar with these systems and committed to following the manufacturer’s installation instructions.

William A. Hayward Jr. AIA, CSI, CCCA, LEED Green Associate, a senior associate and architect with Michael Baker International’s Tampa location, stated, “If designed and installed properly, then metal roofs perform well in Florida. The key to success is in the details regardless of the material type/product.”

But before a commercial roofing project reaches the installation stage, architects are strongly advised to ensure that the metal roofing systems they select meet several key testing protocols. By understanding these tried-and-true wind resistance tests and standards, and better visualizing how high winds can impact product performance, architects will be much better informed when designing metal roof systems. As well, this knowledge is valuable to the specifiers when creating the project specifications.

In addition, an analysis of roofing successes and failures in the aftermath of a high wind event provides valuable lessons learned in approaching the next tornado and hurricane season.

Metal Roofing Panel Types

Prior to delving into the details of the different tests and standards that the metal roofing industry relies upon, an overview of metal roofing panel types is in order.

Mechanically Seamed Standing Seam – One of the more popular metal roofing systems, mechanically seamed panels offer a sleek, modern appearance. Because the panels are seamed together mechanically and are installed to the roofing substructure with clips, the surface has no exposed fasteners and is therefore better protected from moisture, UV rays, and other elements that can cause the fastener to wear over time.

Snap-Type Seam – A type of standing seam roof, the male and female legs of the panel are snapped together creating the seam, with no need for mechanical seaming. They require less labor and are less expensive to install than mechanically seamed panels.

Batten Seam – In a metal batten panel roofing system, a vertical leg is formed as an extra water barrier, with a wide batten seam creating bold aesthetics.

Two-part Batten or Standing Seam – the two panel legs are roll-formed and then butted one next to the other. A metal cap, batten, or standing seam style, is then used to create a seam. As the seam is a separate component of this system, designers can select contrasting colors for the panels and caps, if desired.

Shingles – Lightweight metal shingles help buildings better blend in to surrounding structures, while still benefitting from the durability, longevity, and thermal performance properties of a metal roof.

Shakes – Mimicking the look and style of wooden shingles, shake-inspired metal roofing panels offer a more classic look.

Tiles – Tile-inspired metal roofs are a more cost-effective and lightweight option delivering a high level of resistance against wind, fire, rain, and hail. Easy to maintain, the metal tiles are designed in the style of clay/concrete tiles.

Insulated Metal Panels (IMPs) – An insulating foam core is injected in between two metal sheets to create insulated metal panels. As a turnkey option—delivering a full vapor and water barrier, and continuous insulation—IMPs are an increasingly popular option.

Roofs fall under two categories from a performance perspective: low slope and steep slope. A low slope roof has a slope of less than 2:12, meaning that for every horizontal foot, the roof level goes up less than two inches vertically. Steep slope roofs have a slope of 2:12 or higher.

Steep slope roofs are lower maintenance as debris rolls off easily and standing water is less of an issue. They offer a more classic, aesthetically pleasing appearance.

Low slope requires fewer building materials and are easier to install. At the same time, they have a great need for proper flashing, drains, and coping. Further, the debris, snow, and rainwater doesn’t flow down as easily, so the roofs need to be maintained and inspected on a more regular basis.