Withstanding Weather Extremes

“For existing buildings or new construction projects that are in areas prone to severe weather events, resilience planning has become an increasing priority,” says Wes Sullens, director in the LEED department at the U.S. Green Building Council (USGBC). “Green building strategies have always been a cornerstone for enhancing resilience, which is why they are included in the LEED green building rating system. We’ve seen owners and investors become more attune to how resilience planning improves their assets and helps address climate risks that can have costly repercussions. Momentum is certainly building around construction strategies and decisions that improve resilience, but more awareness and adoption is needed across the industry. A series of Resilient Design credits are helping guide project teams towards identifying risks and mitigation measures. Buildings should be places for safe sheltering and LEED is rewarding project teams that bridge the gap between designing buildings to be energy efficient, adaptive and resilient to impacts as a result of a changing climate.”

Mark D. Webster, senior consulting engineer, Simpson Gumpertz & Heger, Waltham, Mass., says climate-resilience features should be integral components not only of the design of the building but also of the emergency management cycle of essential facilities. “Climate resilience should be accounted for in the planning, preparedness, response, recovery, mitigation and adaptation components of emergency management. With this said, one of the greatest challenges we currently face is the protection, retrofit and/or rehabilitation of the inventory of existing buildings in areas exposed to extreme weather and climate events. The solution to this problem involves a community-wide effort that should incorporate public policy, potential changes in land use and zoning, the development of enhanced design standards, etc.”

ON FIRE

Fire resistance is a primary reason that metal is the preferred construction material for many building applications and the exclusive choice for some entire industries. “The benefit of steel is its high flash point, almost three times that of wood, which breeds the notion that steel won’t add fuel to a fire,” says Brian Shelton, marketing manager of Chief Buildings, Grand Island, Neb. “To further protect the structural members and prolong a building’s structural integrity, spray-on fire proofing can be applied to the bare metal.”

“With many of our housing projects being in California, we are seeing much more fire-resistive materials being used,” says Tom Pflueger, housing studio director, MBH Architects, Alameda, Calif. “Also, the different types of metal, from steel to zinc to aluminum provide for a number of architectural options and applications. Metals are a resilient material and have more longevity than other materials, and we are using it more often as an architectural feature of the building.”

Kyle Rowe, strategic accounts manager, Atlas Roofing Corp., Atlanta, explains that due to its inherent fire-resistant properties, Polyisocyanurate (Polyiso) can be used in a wide range of roof and wall assemblies. “With its high R-value and multiple control layers, Polyiso insulation meets the widest range of code-compliant roof and wall assemblies with regard to fire, vapor, moisture and thermal properties. It is durable, lightweight and easy to use, and is the preferred insulation choice in commercial roofing and wall assemblies. Polyiso chars in place and does not melt or drip like other foam plastic insulation products.”

WINDS

A significant risk for many buildings is the roof’s ability to protect against extreme winds. Dr. Ricardo Medina, staff consultant, Simpson Gumpertz & Heger, says wind is often “a controlling design consideration” in metal building design. “To the extent that wind loads increase, to meet tornado and hurricane resistance criteria, this will be challenging for metal buildings,” he adds. “Ultimately, metal buildings may consider incorporating dual-skin systems in roof and wall construction, with insulation placed in the cavity. The inner skin would act to provide lateral bracing for framing members under suction loads and also act as a form/stay to retain the insulation system, addressing both energy conservation and wind resistance simultaneously.”

Project design teams should ensure they’re adhering to FEMA standards for different wind zones. “Severe wind from storms can easily uplift roof materials, so those that fortify to avoid roof blow-off and help attach the roof to the roof framing and/or walls in order to anchor it is encouraged,” Sullens explains. “Roof hardening methods are also important in protecting against wind and rain. Parapets are an important place to consider weatherproofing using flashing and coping procedures that protect the roof and walls.”

To combat high winds, Tomás Jiménez-Eliæson, community design principal and partner at Little Diversified Architectural Consulting, Durham, N.C., says his firm is combining high performance with zero energy design in hurricane-prone areas, by removing all roof penetrations—which he says are the largest air Infiltration culprits—and ballasting solar photovoltaics. To turn negative wind forces into a positive, for its design award-winning design project Navae Vitae, his firm used lightweight hollow metal spheres with prefabricated internal fins. “These metal spheres that we called ‘wind ivy,’ would capture the northwest winds off the Pacific Ocean and convert that captured wind to energy,” says Thomas Carlson-Reddig, Little’s community practice leader and partner.

Manufacturers are providing designers with many diverse closure solutions to meet extreme winds such as Mountain Top, Pa.-based Cornell-Cookson’s StormDefender Door. Designed specifically with life safety in mind for safe room protection against tornadoes and hurricanes, it is available in fire-rated and non-fire-rated models, and is tested and certified to stringent ICC 500-2014 and FEMA P-361, third edition code standards, says Siva Davuluri, vice president of marketing at CornellCookson.

Shelton believes designing for high-wind situations happens every day, but site conditions may play a more important role to the building’s performance than the actual design. “Building geometry is critical, and the building designer can provide guidance for any specific case. Local topography and the level of unobstructed area around a building often times can’t be changed, but proper planning can reduce the effects of heavy gusts and straight line winds. Adjusting the building orientation and positioning natural or man-made wind breaks can be time and money well spent.”

HIGH HEAT

Cool roof options are at the front line when combating extreme heat from the sun. Utilizing high-reflectivity roofing materials, like those that meet the Cool Roof Rating Council’s standards, reduces heat gain and supports LEED’s Heat Island Reduction credit.

“Limiting thermal emittance and maximizing solar reflectance are important factors and that begins when choosing the exterior paint,” Shelton says. “Because metal panels are pre-coated and since metal buildings are designed as systems, the panel selection is integral to the design of the structural system when energy efficiency and air conditioning performance is top of mind. High-performing insulation packages, and the massive depth that commonly goes with, are also heavily considered when designing the structural steel package of a metal building system.”

Jiménez-Eliæson asserts the heat Island effect is very real in our cities and a large contributor to higher temperatures. “High albedo (light color) roofing materials and green roofs are helping us curb high indoor temperatures in buildings. We are concentrating on designing extremely well insulated and detail high performing walls that minimize air infiltration. This three-year ROI investment can reduce energy demands by 75% as proved at our newest Orlando, Fla.-based school, Neocity Academy, the first zero energy school in Florida.”

To combat the high heat of the Southwest desert, Phoenix-based Benjamin Hall Design has used a rainscreen approach by using metal that becomes superheated, but is held off its exterior walls. Founder and designer Benjamin Hall says, “This creates an air gap between the façade and the mass of the building. The metal skin system has a 2-inch gap behind it and a protective building wrap that can endure high temperatures. The air behind the metal begins to increase in temperature. The air begins to rise naturally and vent out the top. While cooler air is allowed to be drawn from below replacing the rising hot air, thus creating a circulation of moving air that is naturally ventilating itself, which in turn mitigates the heat from being fully absorbed into the mass of the walls.”

Rowe contends in addition to its inherent fire-resistant properties, Polyiso roof and wall insulation products’ higher R-values keeps buildings well insulated in cold conditions but also allow indoor temperatures to remain comfortable under high heat conditions. “Additionally, by exceeding the code requirements for continuous insulation, if a heat wave were to occur, the strain on HVAC systems could be minimized due to enhanced insulation,” he says.

For these extreme weather events, Alan Reed, FAIA, LEED AP, principal at GWWO Architects, Baltimore, explains that generally, resilience codes are fairly current and applicable. “[However,] I do think we will see those codes shift somewhat as the frequency of storms go up, i.e., more stringent hurricane requirements may be required in areas that are not typically prone to hurricanes. With regard to heat waves, flooding, etc., that are less definable, we tend to take a more common sense/ passive approach. For example designing buildings with larger overhangs and natural cross ventilation in areas prone to heat waves, or exceeding code requirements for some issues such as flooding or sea level rise. The codes and regulations—especially regarding sustainability—often dictate a minimum response; however, we tend to look at the potential risks on a case-by-case basis, since as architects, we are responsible for protecting the health, safety and welfare of the public.”

Reflecting the needs of climate-resistance in building design, today’s building codes are increasingly addressing extreme weather events. “Hurricane-resistant design requirements, in addition to design for high winds, now also address coastal flooding, minimization of aggregate-ballasted roofing, and provision of impact resistant exteriors,” says Ronald O. Hamburger, SE, senior principal, Simpson Gumpertz & Heger, San Francisco. “These requirements, which originated in the South Florida Building Code, 20 years ago, have slowly made their way into national design standards. ASCE- 7, the national standard referenced by the codes for structural loading adopted a tsunami-resistant design chapter in its 2016 edition. The 2022 edition of the ASCE 7 standard will likely include requirements that flood-resistant design consider sea level rise and may also include requirements for tornado-resistant design, something that is not presently required by the building codes.”

ENVELOPE AND ENCLOSURE

Unfortunately, many buildings today are still being constructed to meet minimum building code requirements. These requirements are generally based on past weather trends and extremes and do not consider future weather realities. However, according to Scott Armstrong, project principal at WSP-Canada, Toronto, “Diligent building developers are beginning to realize the importance of future proofing, and we are beginning to see a promising increase in awareness and action on this front.”

According to Nicole Parsons, project manager at WSP-Canada, Hamilton, Canada, some more common building enclosure measures being implemented include reducing the window-to-wall ratio, tuning solar heat gain in response to anticipated solar gains, and improving airtightness. “While passive heating via solar gain in winter is beneficial to reduce heating loads, we know that our climate is warming with the expectation for longer heatwaves and hotter overall temperatures. Thus, it’s important to acknowledge that too much glass or glass with the wrong performance parameters can overload the cooling system and contribute to summer overheating. Further, building enclosures must be properly designed and constructed to manage the increasingly frequent extreme rain events we are seeing. Pressure-equalized rainscreen façades and bulk water management on roofs, podiums and plaza decks are critical design considerations.”

Due to more extreme climate/weather events, architects at Little Diversified Architectural Consulting are designing their envelopes in a more robust way. They are not only optimizing R-values, but designing much tighter envelopes with minimal penetrations. “Eliminating thermal bridging and tighter building envelopes can help tremendously in withstanding extreme temperature swings,” Carlson-Reddig says. “We have also reassessed insulation material to make sure that we are not using materials that release toxins in case of a fire. With regard to flooding, we are trying to raise the buildings higher than the 100-year flood zone without compromising accessibility.”

As climate extremes change, building performance targets are changing. Window-to-wall ratio is a key component to consider when optimizing the enclosure’s impact on a building’s energy use, and this metric is increasingly emphasized in North American building standards. “Through these changes, metal has and continues to be one of the most reliable materials to create opaque wall areas,” says Hannah Thevapalan, M. Eng., project manager at WSP Canada, Hamilton, Ontario, Canada. “With the many thermally broken and low conductance cladding support systems on the market today, lightweight cladding panels, such as metal, are easily installed in pressure-equalized rainscreen assemblies, which are also able to achieve excellent thermal resistance. The inherent characteristics of metal panels—such as thermal expansion and contraction—is an advantage when designing resilient buildings. Metal’s properties in extreme temperatures are well understood; this allows designers to incorporate metal into buildings that can adjust to future climate changes.”

INTEGRATED WEATHER DESIGN

Through an integrated design process, project teams can make decisions about how best to respond to weather extremes and build resilient structures. “Designing resilient buildings from the outset will minimize costs and allow for creative problem solving,” Sullens says. “On the contrary, when you start thinking about strategies after the fact it can lead to additional costs. You want those decisions integrated into the project from the beginning.”

Shelton agrees designing for extreme weather events starts very early in the building process. “So, unless we are involved early, such as in a design-build situation, the metal building manufacturers are usually relegated to providing the resources but not the methods employed. When our role is product supplier only, our scope is limited to the impact of those efforts. The American Society of Civil Engineers, Metal Building Manufacturers Association and American Institute of Architects are some great resources for information on resilient design. The AIA even offers an online certification program on the subject of resilient design.”

Sullens suggests consulting USGBC’s Center for Resilience as a resource for project teams looking to prioritize resilient design. “It houses all of the organization’s resilience activities and provides guidance and resources demonstrating how addressing and emphasizing resilience through green building certifications can help ensure a more resilient future for all.”