Against the Wind: MBCI’s Wind Rating Dominance

After a major, damaging storm, such as hurricanes and tornadoes, many things happen at once. Rescue efforts begin. Shelters open to house the displaced. Cleanup gets underway. But one thing that happens in the aftermath of such an event is a little harder to see – unless you’re looking for it.

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The Building Material Post-Mortem

The Roofing Industry Committee on Weather Issues, Inc. (RICOWI) gathers experts and an army of volunteers to spend time on the ground at the disaster site, documenting damage. They take careful notes and photographs, looking closely at how different building methods, materials and ages withstood the storm. What they observe helps inform product development and ensure both installation standards and roofing products can stand up better to the next storm.

Unabbreviated

As the Metal Construction Association’s technical director Robert Zabcik said in a recent white paper, “Engineering professionals go through great efforts to make sure the public is protected.” All this research is integrated into regular updates to the tests, ratings and codes applied to building products across the country. These can become an alphanumerical soup, but here are the most prominent, along with differences between them:

Model Codes (Codes) provide a minimum baseline of performance needed to protect property and the public. These are the barebones building basics.

Underwriter’s Laboratories (UL) is a consortium of test labs and research companies which maintain test standards, as well as product listings which meet certain performance criteria. These are usually superior to those required by code.

Factory Mutual Insurance Company (FM Global) is comparable to UL but funded by a consortium of insurance underwriters.

Since the Miami-Dade area has suffered some of the worst hurricane damage, they have some of the most stringent codes and test protocols, so those are among many that MBCI uses to test our products. Jason Allen, MBCI research and development engineer, explained what some of these are and how they’re used. The UL 580 rating is based on tests for uplift resistance of roof assemblies. While materials can receive a class 30, 60 or 90 rating, MBCI uses class 90 as a standard. We also maintain class four impact ratings under UL 2218 for hail and projectiles, as well as the UL 790 Class A fire rating.

Any Way the Wind Blows

But these ratings and classifications get very complicated. You won’t find MBCI materials themselves listed as withstanding certain windspeeds or projectile damage. Allen explained, “It’s dependent on several things: building codes, roof pressures, eave and building height, facing attachments, roof slope and wind speed – just to name a few.” There are differences based on locality, storm threats and codes. It takes a qualified engineer to calculate all of it for an entire project. But that’s the only way to be sure of safety. “It’s going to cover all scenarios,” said Allen.

During a hurricane or tornado, wind is just part of the problem. “Performance during these events must consider both water tightness and wind applied at the same time,” said Zabcik. “Wind-driven rain can force water into places it would not normally go … This is yet another reason why details are so important and why manufacturers work so hard to ensure the systems they produce meet stringent standards for performance.”

In conditions like these, traditional building methods have a difficult time comparing to metal. They suffer from softer connections, more porous materials, and less stringent assembly designs. “Shingles last 15 to 20 years,” said Allen. “A metal roof can last 40 to 60 years.” Across the nation, wherever post-storm studies and material testing have occurred, metal stands out. In Florida Building Commission, FEMA and NIST studies, metal buildings performed exceptionally well.

Second Wind

Whether standing seam, insulated metal panels, exposed fastener or concealed fastener roof solutions are chosen, metal roofing’s strength and durability keeps out rainwater and withstands windspeeds that devastate other types of construction. Standing-seam roof systems and IMP façades remained intact during Hurricane Katrina even as winds hit 120 mph. “Industry experts have found that metal panel roofs can withstand wind gusts as strong as 140 mph or more due, in part, to their large interlocking panels,” said Zabcik. “Metal panel systems provide not only the weather resistive barrier,” he said, “but can also provide diaphragm stability to both the underlying framing and sometimes, the building as a whole, because they can transmit shear from one panel to the next.”

Riders on the Storm

What about hail raining down from the sky, windborne projectiles, lightning, and everything else that severe storms hurl at buildings? Though they may suffer some cosmetic damage, metal construction such as standing seam roofs and IMPs are often able to absorb impact, remain functional and keep their protective metal layers intact. That can make all the difference in a hurricane when the wind can blow away other roofs and dump untold gallons of stormwater and debris inside. Somewhat counterintuitively, metal buildings also perform very well during lightning strikes.

Batten Down the Hatches. Then Batten Them Again

Before you assume that selecting an engineer’s recommended, rated, and tested metal roof will be a sure-fire protection against all nature’s hazards, there’s one more thing to understand. All the ratings and tests mentioned here are performed with a specific assembly procedure. It is absolutely critical that the same procedure is followed – to a T – to ensure your building will enjoy the same protection its ratings guarantee. Allen recommends that you “look at the company you want and make sure they have statewide approvals,” and make sure your installer reads the manual, then re-reads it, then re-reads it a final time. It’s no exaggeration to say that lives are at stake.

Zabcik sums it up nicely: “With proper preparation, a solid knowledge of metal roofing options, an understanding of the latest standards and codes – not to mention a willingness to strictly adhere to tested quality control methods – today’s metal roofing is a strong choice for even the most vulnerable structure.”

To learn more about MBCI roofing solutions, to retrofit a current building or to get an engineer started on designing out your project in a storm-prone area, get in touch with an MBCI representative today.

Metal Roofing Considerations for Coastal Areas

Whether it is wind speed, sun exposure or the proximity to a coastline, these factors would be the major considerations when choosing metal roofing for a project in coastal areas. The good news is that metal panels can be used in just about any coastal area so long as you find the right product profile and finish that meets your specific requirements to maximize performance given the variables of the environment.

There are a number of special considerations given the environmental conditions inherent to a coastal area, including the impact to paint systems and certain unique maintenance requirements, wind ratings, hurricane conditions and certifications/regulatory product approvals that will limit the panels you can you use within specific coastal areas, for instance Dade County, the state of Florida, and the Texas Coast.

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Finishes: The 1,500-Foot Rule

Metal components can be a great roofing choice, even in a coastal area, whether a bay, gulf, or ocean water. Key is how you manage the finish on the products and how close you are to the actual salt environment. Simply stated, if you’re outside of a 1,500-foot range from the coastline or salt water, then standard metal roofing would be suitable, but if you’re closer to the coastline there are special paint options or finishes you’d need for the product to withstand the coastal environment.

At MBCI, we use Flurothane Coastal coil coating system* as our standard solution to the challenge of salt spray and harsh coastal environments. This coating is a premium fluoropolymer (PVDF) system developed for use in the most extreme coastal environments. This system is unique in its use of an innovative thick film primer. The two-coat system has a total dry film thickness (DFT) of 1.7 to 2.0 mils.

Choosing an appropriate coastal finish can also affect your product’s warranty. If, for example, your project is within the 1,500-foot range and you don’t choose the required coastal finish, if the panels were to rust there would be no warranty offered and it could affect your warranty for weathertightness as well.

Suitable Panel Types and Additional Coastal Conditions

Overall, roof failures are the largest hurricane loss due to wind and water damage. For this reason, metal roofing is a highly recommended option for coastal regions where hurricanes and high force winds are prevalent. The appropriate metal panel type for these areas is mainly contingent upon what you want to accomplish. Because MBCI does have high wind ratings for most of our panels, whether it be a screw down (aka through-fastened) panel or a standing seam profile panel, selections should be determined by the complexity of the roof itself and the roof conditions. There are standing seam panels and through-fastened panels that can be approved for both roof and wall applications in many coastal areas.

Also, of note, different types of coastal areas may receive higher wind speeds. There is obviously a wide difference in wind speeds between the East Coast and the West Coast, for example, although both are coastal communities. In an area with higher wind speeds and/or hurricane conditions, you would want to consider panels that achieve higher wind ratings. Since there are many different panel options, and some may not be able to achieve as high wind ratings as others, you should look at what those values would be for wind and what testing has been done. MBCI’s metal wall panels and roofing systems are able to resist and withstand extreme environmental conditions, such as those in Florida or the Texas coast where strict product approval and testing processes are required.

MBCI has panels that meet requirements for Florida Approval, Dade County and Broward County for instance, where you need to have an NOA (Notice of Acceptance) for those county areas, as well as products that are TDI approved (Texas Department of Insurance), which is usually seen in the Texas coastal area.

Additionally, sun exposure and color can have an impact as far as solar reflectance, so that is another consideration. Somewhere like Florida gets a lot of sun yet a coastal area in Washington State would be mostly cloudy. If you are in an area that has more sun, then you may want to consider a panel with a higher solar reflectance value.

Maintenance Requirements

If you have metal roofing in a coastal area, you’re going to follow much of the same maintenance as you would on any metal roof, but you would want to inspect it for damage, especially after a wind event or storms. One of the main differences, though, especially if you’re within the 1,500-foot limit where you needed a special finish, is that you’re going to have to do a fresh water rinse regularly on the panels a couple of times a year. What this means is you are basically hosing it off with fresh water to get the potentially corrosive salt spray residue off of it.

For more on metal roof and wall panels and finishes for use in coastal areas, contact your local MBCI representative.

 

* (1) All substrates must be properly pretreated. (2) American Society for Testing and Materials. (3) Flurothane Coastal system is not designed to bridge cracks in the substrate. (4) Varies by color. (5) Flurothane Coastal system will generally meet the requirements for most post-painted fabrication processes. However, variations in metal quality, thickness or cleaning/pretreatment applications can lead to diminished flexibility.
SOURCE: Valspar Corporation

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