A Common Misconception About Determining Thermal Resistance

Photo courtesy of ENERGY.GOV

Photo courtesy of the U.S. Department of Energy

As an architect, you’re required to design a building’s wall to meet the code-required R-value (or U-factor) in the International Energy Conservation Code. So you design the wall and add up the manufacturer-stated R-values of the components.  Done, right? That method only makes sense if walls have no joints, seams, windows, or doors! Let’s think about this.

Accounting for Thermal Discontinuities

The manufacturer-stated R-value of an insulated metal panel (IMP) should really be the R-value in the center portion of the panel, if the manufacturer uses terminology consistent with ASHRAE 90.1. However, a wall is made up of many IMPs, and there are joints between the IMPs.  We’ve all seen the infrared photos showing the heat loss at joints between panelized anything—plywood, insulation boards…and IMPs. The joints between each and every IMP are thermal discontinuities, commonly called thermal bridges. These are locations where the R-value is not what you read in the manufacturer’s literature. There are also metal clips and attachments that reduce the R-value of the IMP wall system. If you’re designing a wall system, don’t specify the R-value of the panel and assume it is the R-value of the wall system!

Calculating the R-Value of a Complete IMP System

A building owner deserves a wall that meets or exceeds the code-required minimum R-value or U-factor. The mechanical engineer needs to properly size the building’s mechanical systems based on the ‘real’ characteristics of the building envelope.

Let’s put some numbers behind this idea. Let’s consider a 42 inch-wide panel, 2 inches thick, with a stated R-value of 12. The outer surface of the panel is close to the exterior temperature—say 30 degrees. The metal wraps through the joint, decreasing the temperature of a portion of the metal on the backside of the panel everywhere there is a joint. Clearly this reduces the overall R-value of the IMP as a system.  Let’s estimate that the thermal bridging effect of the joints reduces the R-value 5 inches along the edges of the panels to an R-6. That means 30 inches of the panel has an R-12, and 10 inches of the panel has an R-6. That calculates to an average R-value of 10.5 for the panel overall, which is more than a 12% loss of R-value. This is why blindly using the famous equation of R=1/U is dangerous. That equation is only true if the R-value and U-factor involved are consistent with how thermal bridging is or isn’t represented.

U-Factor Testing for Higher Accuracy

It’s clear that the panel joints are thermal bridges, but the extent of loss is really an educated guess. But there is a solution! The forward-thinking IMP manufacturers are performing U-factor testing and finite element modeling, and that includes joints between panels. The U-factor testing is a more accurate determination of thermal resistance.

As an architect designing the wall system, if you use stated R-values, recognize that you’ll need to account for the loss of R-value because of the joints. Or, simply specify panels whose manufacturers are determining the U-factor for their IMPs!

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Wellness and Envelopes: Four Ways Single Skin & Insulated Metal Panels Keep Us Healthy

SONY DSCIs there a connection between building design and human health?

We know the answer must be yes, but figuring out how the connection works is the job of experts like the team behind the WELL Building Standard®, a new certification that takes on the question. Among the solutions that can help make a building better? Metal roofing and siding, according to many healthy building experts.

First, let’s learn about WELL. According to the International WELL Building Institute, the WELL Building Standard “takes a holistic approach to health in the built environment addressing behavior, operations and design.” Their performance-based system measures and monitors such building features as air, water, nourishment, light, fitness, comfort, and mind. Two ratings have been offered: WELL Certified™ spaces and WELL Core and Shell Compliant™ developments. Done properly, these “improve the nutrition, fitness, mood, sleep patterns, and performance of occupants.”

Pilot programs are currently available for retail, multifamily residential, educational, restaurants and commercial kitchens projects. In many of these projects, the use of metal claddings and insulated metal panels (IMPs) is recommended by many health-focused professionals. Why?

1. Occupant comfort. IMPs tend to have excellent R-values and very good thermal efficiency – including long-term thermal resistance, or LTTR, a key measure of how the building will perform over time. For the wellness factor from pure thermal comfort, IMPs are highly effective over conventional construction.

2. Nourishment of people and earth. IMPs are often made with recycled metals and improve the energy performance of the building. With energy cost savings ranging from 5 percent to 30 percent, they cut the carbon footprint of the facility. Plus the interior and exterior skins include up to 35 percent recycled content – and they are 100 percent recyclable – reducing impact on the global carbon load.

3. Daylight for all. Using metal roofs with skylights or light-transmitting panels in conjunction with integrated dimming lighting is a highly cost-effective strategy, and IMP systems also have integrated window systems that increase available sunlight within building interiors. Light is essential for healthy buildings, and daylight is the best kind of all.

In addition, because rigid insulation per inch offers more R-value than per inch of fiberglass insulation and IMPs have metal liner skins, day-lighting fixtures such as light tubes can be integrated more easily with these roofs.

4. Proper moisture and air control. Issues such as leaky walls and wet, moldy construction materials are anathema to wellness, and must be controlled for healthy building certifications. Mold has a negative impact on indoor air quality and indoor environmental quality, and one of the main culprits is trapped moisture. This can also corrode the metal studs and furring members, even if they are galvanized, leading to structural issues such as reduced fastener pullout resistance and leaks.

How Does a Building Become WELL Certified?

IMPs used as either rainscreens or as sealed barrier walls backing up a rainscreen are shown to protect against moisture issues and mold over time. They also serve as a continuous layer of insulation and air barrier. In this way, the single-component system can eliminate the need “for air barriers, gypsum sheathing, fiberglass insulation, vapor barriers, and other elements of a traditional multicomponent wall system,” says one industry executive. In fact, many masonry buildings are being upgraded with IMP retrofits on the exterior, directly over the old concrete, brick or stone.

All of these traits of IMPs certainly contribute to more healthy buildings, but do they add up to WELL Building certification levels, such as Silver, Gold or Platinum?

To get there, building teams must undergo an on-site WELL Commissioning process with rigorous post-occupancy performance testing of all the features. If it meets the “preconditions” — the WELL features necessary for baseline certification — WELL Certification is given. If the team pursues “optimization features,” the higher levels of achievement are granted.

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Fire resistance of metal panel roof systems

Ditch Witch (12)Metal is inherently fire resistant.  The codes acknowledge that; however, certain limits are placed on metal’s fire resistance when used as part of a metal roof system.

Metal panels transfer heat very well—they get hot quickly and give up heat quickly.  And, in many cases, there is a building component (roof deck, framing) directly under metal panels.  Metal roof systems are required to be fire classified because of the concern about the combustibility of the materials under the metal panels.

Fire Resistance Classifications

The 2012 and 2015 IBC, in Section 1505 of Chapter 15, states that fire classification of roof assemblies is based on two tests—ASTM E108 and UL 790—that are fundamentally identical.  Each requires a spread of flame test and a burning brand test.  Tested roof systems are fire classified Class A, B, or C, where the most fire-resistant roof assemblies are Class A, and Class C is least resistant.

Building Code Fire Resistance Requirements

Building codes establish fire resistance requirements for roofs based on the type of construction (e.g., concrete/steel, wood) for the building.  A common misconception about roofs’ fire ratings is that building codes require Class A.  Not true—the IBC does not require Class A roof assemblies for any type of construction!  Only roofs on buildings located in wildfires zones (e.g., Southern California) will likely be mandated to be Class A.  (It is worth mentioning here that the vast majority of low- and steep-slope roof systems sold and installed in the U.S. are Class A.)

The building code lists a number of roof types deemed to be Class A (in other words, testing is not required).  Appropriately, metal panels are included: ferrous (steel) and copper shingles or sheets, metal sheets, and shingles on noncombustible decks (e.g., steel, concrete—not wood), or on noncombustible framing where a deck is not included (e.g., directly over metal purlins).  The key is that the deck or framing is noncombustible.

If metal panels are installed over combustible decks, the assembly needs to be tested using ASTM E108 or UL 790.   An exception for combustible decks is that 16 oz./sq. ft. copper (or thicker) can be installed over combustible decks and be considered Class A without testing.

Building with Fire Safety in Mind

The code requirements for fire resistance of metal panels are logical and not overly burdensome.  Most metal panel manufacturers have tested their roof assemblies, and most, if not all, metal panels and shingles can be used in Class A fire-rated roof systems.

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Reroofing with steep-slope metal panel roof system over an existing low-slope roof: Part 1

Reroofing w Steep Slope

You’ve probably seen many articles and photos of buildings with low-slope roofs converted to steep-slope metal panel roofs.  Aesthetics and leakage are driving these conversions, but mostly leakage of the low-slope roof.  Owners are frustrated with leaks and believe a steep-slope metal roof is their answer, and it certainly can be!  There are a number of issues to be resolved and decisions to be made to ensure long-term performance of the new metal roof.

Retrofitting a roofing system

A new structure, such as MBCI’s retrofit systems, should be attached directly to the existing structural members.  Removal of small sections of the existing roof is required for direct attachment.  Fastening through the existing roof means attaching through a soft substrate, allowing for compression over time and movement of the fasteners, and their eventual loosening.  If possible, installing new flashing at the attachment points (with spray foam?) provides a second water barrier.

Steps to take after retrofit installation

Conversion to a steep-slope metal roof creates an attic space that now needs to be ventilated to remove heat and moisture, but also to provide adequate airflow for HVAC intake requirements.  Determine intake air requirements—how many air changes per hour are required in the attic to satisfy fresh-air intake requirements?  Significantly more than code-required ventilation amounts may be needed if many HVAC units are enclosed.  Inadequate ventilation could result in an extremely hot and humid attic space and overworked mechanical intakes.  Poor ventilation could increase the need to cool a building, especially single-story buildings (e.g., schools) converted from low-slope to steep-slope roofs.  Conversely, the vent stacks are also enclosed.  Perhaps vent stacks need to be vented through the roof?

To prevent condensation issues in the newly created attic space, it’s prudent to install mechanical ventilation units that are controlled by a humidistat, not a thermostat.  Maximum humidity levels can be determined for summer and winter seasons, and the humidistat can be set to remove humidity and air when the maximum relative humidity levels are reached.

Drainage at roof edges must be well thought out.  If the new roof includes overhangs, gutters and downspouts and eave vents can be installed.  If there are parapets, creating an “internal gutter” where the new metal roof meets the parapet can be difficult to detail properly for a long-term, low-maintenance solution.  Overhangs and eaves, even where parapets exist, are the best solution.

This is blog one of two.  More on this topic next time!

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Passive aggressive: Metal buildings suit passive house standards

Today’s big push toward Passive House standards — the formerly German building certification that recently gave rise to a U.S. counterpart, Passive House Institute US, with its PHIUS+ certification — is also creating more interest in the highly efficient, highly insulated metal buildings. The projects range from metal-clad houses to IMP commercial facilities to the first Passive House high-rise in the world, Cornell University’s 26-story residence tower, clad in metal panels.

Metal? That’s right. While this surprises few design and construction professionals, consider these facts: (1) IMPs and metal roofs protect their insulation backup better than many kinds of construction methods, ensuring good long-term thermal resistance, or LTTR. (2) Passive House requires airtight construction with minimal air infiltration, which is ideal for the tight, engineered construction and inherent air barrier quality of metal panels. (3) Metal roofs and walls are available with high-efficiency Energy Star windows and skylights that are designed to integrate with the cladding and roofing systems.

Photo courtesy of www.phius.org

Photo courtesy of www.phius.org

These reasons also explain why IMPs have been used extensively for net-zero energy buildings in recent years, which also demand highly energy-efficient enclosures along with the means to produce energy with solar heating, photovoltaics, geothermal and wind turbines.

So when it comes to Passive House and the PHIUS+ certification, often the choice of insulated metal panel (IMP) systems is among the first major project choices. Two immediate benefits arise, says the Metal Construction Association, for solar reflectance (SR) and thermal emittance (TE). “Metal cladding has very dependable and high SR and TE values, and it employs polyurethane foam, one of the most efficient types of insulation, which maximizes building energy efficiency,” says Ken Buchinger, general manager of Technical Services with MBCI.

Coupled with the robust barrier provided by coil metal and the tight construction afforded by pre-engineered, prefabricated panel systems, the resulting enclosure type is among the most efficient available. And that’s not just for new construction: A large number of Passive House projects have retrofitted IMPs over leaky existing buildings of masonry, brick or stucco. In its certification guide for PHIUS+, the Passive House Institute US specifically cites metal roofing and metal cladding systems to meet the rigorous criteria.

For the net-zero approach, Buchinger adds that solar photovoltaic systems and solar water heating systems can be installed on a metal roof, penetration-free, resulting in high performance with minimal risk. “Metal roofing, known to last 60 years or longer, is the only roof type that can outlive a PV system mounted on it, meaning zero maintenance and low in-place cost for the roof and PV system together,” he explains.

Whether the approach is passive or zero, we’re seeing a new generation of super-efficient buildings today. New certification rules were unveiled this year for the Passive House standard have lots of buzz. And the latest projects, many with metal wall and roof panels, have resulted in facilities using as little as 10% of the energy required for comparable projects, according to PHIUS.

That’s why passive design sounds pretty aggressive for going green.

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Codes: More than the IBC and IRC

IBC IRC CodeWe all know to look to IBC Chapter 15 and IRC Chapter 9 for information about roof systems.  These two “Roof Assemblies and Rooftop Structures” chapters include the requirements for fire, wind, impact, materials, and reroofing.  But did you know the scope of the building code (IBC Section 101.4) references additional model codes that are considered to be part of the requirements of the IBC?  From a roofing perspective, this scoping reference brings into play the International Energy Conservation Code (IECC) and the International Existing Building Code (IEBC).

The creators of the model codes are attempting to ensure that buildings (and roofs, in our case) are designed and built according to the most recent model codes even if they haven’t been specifically adopted by a state or local jurisdiction.  If a jurisdiction adopts and enforces the 2015 IBC, by reference the 2015 IECC and 2015 IEBC are in effect.

How do 2015 IECC and 2015 IEBC affect roofs?
The IECC Commercial Provisions include energy efficiency requirements for the same buildings for which IBC Chapter 15 roofing requirements are required.  The IECC includes minimum insulation, air barrier, and reflectivity requirements for building envelopes.  Prescriptive R-values and U-values are provided for roofs, and they are based on climate zone, metal buildings, and attics.  Minimum levels of solar reflectance and thermal emittance are required for low-slope roofs on buildings with air-conditioning in climate zones 1, 2 and 3.

Air barriers—used to reduce or eliminate air leakage—are required for new construction.  These are based on materials, systems, or the whole building.  Sheet steel and aluminum are listed as materials that meet the air barrier requirements.  Of course, the joints and seams are critical to the effectiveness of metal panels when considered to be air barriers.  When reroofing, air barrier requirements are not triggered, which is significant.  But the insulation requirements are triggered.

Roofing and structural considerations
The 2015 IEBC includes sections about reroofing (Section 706, which is new in the 2015 IEBC) and structural considerations (Section 707).  The IEBC divides “Alterations” of buildings into three types: Levels I, II and III.  A level I alteration includes the removal and replacement of existing materials.  Reroofing is a level I alteration, which triggers the requirements of Chapter 7.  The Structural section includes a requirement to upgrade a wind-resisting roof diaphragm when more than 50 percent of the roof is removed where the design wind speed is greater than 115 mph, and in special wind zones.  While these are small portions of the United States, it’s important to understand this requirement.

Build roofs with the full scope in mind
Look beyond the roofing chapters to ensure that you design and build buildings according to the most recent building codes.

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Ventilation for steep-slope roofs


Ventilation can be a confusing topic.  What is the purpose of ventilation?  Is ventilation required for all types of roofs?  What do the model codes require?

Ventilation, when done properly, removes heat and moisture from traditional attics and from rafter spaces.  The removal of heat and moisture is necessary for buildings to operate efficiently and not deteriorate prematurely.  Ideally, an attic should be the same temperature and have the same humidity level as the exterior.  Convective ventilation—natural air flow from eave to ridge—means air comes in at the eaves and is exhausted at the ridge, taking the heat and moisture with it.  Importantly, ventilation is outboard of the insulation layer for the home or building.

The IRC and IBC have very similar requirements, found in the 2015 IBC, Section 1203 and the 2015 IRC, Section R806.  Ventilation is not tied to the type of roof system installed, as some believe.  Because ventilation improves the overall performance of a building, regardless of roof type, ventilation is required when steep-slope metal roofs are installed.

The amount of ventilation is based on the floor area of the attic.  The ventilating area should be at least 1/150 of the floor area.  Ventilation amounts can be reduced to 1/300 if half of the ventilation is at the eave and half at the ridge.  This allows the convective flow to work efficiently, allowing the reduction in the total ventilation amount.  In climate zones 6, 7, and 8 (i.e., the northern third of the US), an air barrier is required at the ceiling level in order to use the reduced amount of ventilation (i.e., 1/300).  A vapor retarder reduces the amount of moisture that can accumulate in the attic space; therefore, less ventilation is needed and required.

Because the model codes discuss ventilation only for attics and enclosed rafter spaces, the requirements are necessary only for steep-slope roofs.  Low-slope roof systems are not installed over attics or cathedral ceilings; therefore, the requirements for ventilation aren’t triggered when a low-slope roof is installed. Not because of the low-slope roof, but because there isn’t an attic or a cathedral ceiling.

Is ventilation in your scope of work?  In nearly all situations, the metal panel installer will install the ventilation components at the ridge.  And, unless the ventilation at the eave can remain in place, the installer should take the opportunity to install the ventilation components at the eave.  Eave ventilation can easily be made of metal, and can be an “add” to your scope of work for new and replacement roofs.

Understand ventilation requirements, improve long-term performance, and expand your scope of work.

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Part III – Transparency plus consensus: A win-win for everyone

Part III transparency plus consensusIt has been a long time since my last blog on this subject. This is not only because I’ve been busy but also because the landscape of green building programs in general has changed significantly since Part II, and I wanted to wait to see how things shook out before I wrote something that might be immediately outdated. If you remember, we left off in Part II talking about how LEED, the most popular green building program in the US, has not been developed through an ANSI accredited consensus process. Furthermore, the resulting lack of transparency was dubiously ironic given that LEED demands a high level of transparency from building product manufacturers in the latest version of their program, LEED v4.

We also discussed the related but more general movement for manufacturers to fully disclose all of the ingredients in their products to a third party who then compares that list to lists of known hazardous substances and disclose any matches on a product label or public disclosure for all to see. This movement has been fueled by several large architecture firms sending letters to building product manufacturers threatening to stop specifying their products unless they participate. Although most manufactures agree that there is merit to disclosure and are anxious to participate in a fair program, they have not been privy to discussions regarding the logistics of such a program nor have they been allowed to participate in any kind of a standard development governing the disclosure process. This makes manufacturers reluctant to participate, given their vulnerability in such a situation. This risk is leveraged by the fact that currently the only standards that dictate the rules of such a program are under the control of consortiums who have little to no scientific expertise and, frankly, have not been friendly to the building products industry in the past.

I also mentioned that there are alternative programs to LEED that have been developed through a valid consensus process. Specifically, the International Green Construction Code (IgCC), ASHRAE 189.1 and Green Building Assessment Protocol for Commercial Buildings (also known as Green Globes) are ANSI standards that outline the relevant requirements for anyone to view. However, the USGBC marketing machine and resulting popularity of LEED prevented wide use of these standards. Thus, they remained largely unutilized. That is until this year, when the USGBC, IgCC and ASHRAE signed a Memorandum of Understanding, promising to work together and create a favorable consensus by eliminating duplication of provisions and assigning an area of responsibility for each group to maintain separately.

Although no documents have yet to be created, it appears that the administration and enforcement provisions of the new standard will come from the IgCC, and the technical content will come from ASHRAE 189.1, both of which are consensus based. Meanwhile, LEED will require compliance with 189.1 as a prerequisite to an upcoming interim version of LEED. This approach allows an Authority Having Jurisdiction (AHJ) to adopt the IgCC as a minimum standard of construction; dropping any reference to LEED they might currently have as minimum project requirements for all buildings. This leaves LEED to evolve as a completely voluntary program going forward and push the envelope of green building, which is their core mission. Meanwhile, Green Globes remains ANSI accredited and still exists as a commercial competitor to LEED. This environment should result in a more user friendly application process, the lack of which been a ubiquitous criticism of LEED for years, because Green Globes is much more user-oriented.

So, it appears that the most popular green building programs are poised to move in the
direction of a true consensus, which is fantastic news for everyone involved. However, the creation and development of disclosure programs, which will not be in the initial technical requirements provided by ASHRAE 189.1, remains largely a one-sided affair with no seat for manufacturers at the table. Besides the contentious nature of the subject in general, there are major philosophical questions that have to be addressed before Health Product Declarations (HPDs), or any type of disclosure in general, can be brought into the main stream. That subject is beyond the scope of this blog, but I encourage you to read a very good article on the trappings of HPDs called “Disclosure: The Newest Dimension of Green Building” by Jim Hoff.

The good news is that there may be a viable alternative to HPDs on the horizon. ASTM has a current open work item to develop a true consensus based standard guiding the issuance of a Product Transparency Declaration (PTD), which has much the same intent as an HPD. As discussed in Part I, the development of ASTM standards is a highly transparent process that allows everyone, including manufacturers, to come to the table. I encourage every designer to join ASTM and get involved in this process, especially those firms who participated in the letter writing campaign, and forgo HPDs until PTDs are available.

Yes, it will take a little longer; the reality that the development of consensus based standards takes time. But just like the development of the laws that govern this country, there is far too much risk involved in getting it wrong. Instead, having these standards developed by a consensus-based process is the only way the finished product will be truly useful and meaningful.

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Top four reasons to attend trade shows

Trade Show BoothWith phone calls and emails growingly replacing client visits, I think it’s important not to lose sight of the benefits of face-to-face interactions in the business space. With METALCON, a trade show for metal construction products, technologies and solutions, less than a month away (October 14-16 to be exact), I thought it’d be relevant to discuss the top reasons why trade shows are productive for businesses and, specifically, why you should attend METALCON in Tampa, Florida, this year.

Not to jeopardize our audience, I would like to be forthcoming; as a title sponsor at METALCON we have vested interest in driving traffic to the show. That being said, we would not invest in a title sponsorship if we did not wholly support and value meeting and seeing our colleagues and customers in this forum.

  1. Educational opportunities. Although trade shows are widely known as a space for companies to display and educate audiences on their product line, they also provide additional educational offerings on industry challenges and trends. At METALCON, for instance, they offer an entire lineup of relevant courses taught by industry experts to help strengthen your business and two free Learning Zones that host brief, 15-minute sessions that cover topics on roofing details, field techniques and product applications. To view METALCON’s full course schedule, click here.
  1. Putting a face with a name. Trade shows are a forum for customers and sales representatives to interact directly and learn about one another. According to David Brock of Partners in Excellence, “When you know who the customer–the individual—is, what she looks like, what he’s responsible for, how our products help her do her job, the relationship changes.  It’s not a faceless entity, but an individual trying to do his or her job, trying to achieve their goals, trying to reach their dreams–and they need our products to do this.” This personalization deepens the business relationship and improves future communications.
  1. Network and exchange ideas. Aside from interacting with potential and current suppliers, trade shows welcome engagement between colleagues and business peers beyond the show floor. Receptions, such as METALCON’s 25th Anniversary event, frequently follow exhibiting hours daily and give attendees a more relaxed environment to meet others, exchange ideas and form business contacts. In a room full of individuals with shared interests, who knows what brilliant ideas might be born on the back of a cocktail napkin?
  1. Informed purchasing. 81 percent of trade show attendees have buying authority, according to the Center for Exhibition Industry Research. Trade shows bring the latest in product developments, technology advancements and industry trends to you. Housed in one location, attendees can compare the competition directly and formulate educated purchasing decisions based on their findings. With four out of five attendees seeking products or services, the takeaway could save time and provide clarity when selecting suppliers. Click here to view the full list of 252 exhibitors at METALCON.

If the above peaked your interest and you would like to attend METALCON for FREE as our guest click here to register and be automatically entered to win a prize at the show.

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Storms and safety: Metal building systems, standing strong


Brester Construction features eco-FICIENT Royal panels

Welcome to hurricane season, says NOAA! Erika was a near miss, and Henri went off to sea, but with multiple storms stirring up the Pacific and a major El Niño threatening severe weather this year, building teams are focused on resilient, high-performance envelope and roofing assemblies.

Resiliency is the watchword, and the stringent Miami-Dade County code language or similar standards are being adopted in many communities. The Florida Building Commission as well as FEMA and NIST have done studies of building performance during severe storms, and metal buildings were shown to perform exceptionally well. According to MBMA reports, insulated metal panels (IMPs) perform well under stresses of high winds and projectiles such as hail and wind-borne debris.

The post-storm studies everywhere from Texas to New Jersey confirmed the durability and resistance to driving rain and severe pressure differentials, too. Standing-seam roof systems and IMP façades remained intact during Katrina even as winds hit 120 mph. According to Metal Roofing Alliance, “metal roofing can have a 140-mph wind rating, meaning it can withstand wind gusts up to 140 miles per hour.” MBCI, which has achieved these ratings, has also pointed to another critical standard: wind uplift testing in accordance with Underwriters Laboratories’ UL 580, Standard for Tests for Uplift Resistance of Roof Assemblies.

Detailing of the roof-wall interface is essential to protecting against uplift. To reduce damage from wind-driven rain, manufacturers like MBCI use test protocols from Miami-Dade or the ICC (TAS No. 100-95). These standards show the security and integrity of the seams in IMP and metal roof systems. For hail and wind-driven projectiles, the metal systems often are able to absorb impact and remain functional and retain their protective metal layers intact even if they may suffer cosmetic damage, as MetalRoofing.com forums have shown. Last, IMPs and metal roofing systems perform very well during lightning strikes — a fact that is counter intuitive but proven. In fact, use of metal roofs does not increase the chance of a lightning strike, as scientific studies show and the Metal Construction Association reported in BD+C, and as you can read more about in our blog post.

Similar to the three pigs of fable, some buildings will do well through hurricane season, while others nearby will suffer from softer connections, more porous materials and less stringent assembly designs. Many building owners will do well with metal roofing and vertical assemblies: with rugged embossed metal sandwiches over high-R-value, rigid insulation, held firmly in place with interlocking joints or lapping seams.

Best of all, the systems are complete assemblies that install as weather-tight barriers without coordinating various components and trades. They also have higher rated values than, for example, EIFS planks or fiberglass panels, some of which may suffer lost R-value when wet. With these benefits – and following the damage and disruptions caused by Hurricanes Katrina and Sandy in the United States – metal is an attractive roofing choice for weather resistance.

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