Chemistry and construction materials

by Katie Daniel | September 6, 2017 4:20 pm

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by Todd Sims
This year, ‘resiliency’ emerged in the building landscape as more than a buzzword. Many regions around the world are increasingly subject to the rigors of various impacts, including extreme weather, population shifts, disease, power or communication disruptions, and financial shocks. Urban and rural spaces alike require structures able to withstand volatile stresses while reducing the additional resources, time, and labor needed to rebuild and relocate.

Resilient structures necessitate innovative materials that can not only endure stress, but also return to a functioning, usable state. For example, a bridge is resilient if the materials used can expand and contract with cold weather, high winds, and changes in traffic patterns. Specific insulation materials can add strength to walls; they help eliminate the movement of air and moisture while increasing a wall’s resiliency.

Last year, the Resilience Building Coalition, which includes the National Institute of Building Sciences (NIBS), American Institute of Architects (AIA), CSI, and 37 other leaders of America’s design and construction industry, released its first progress report, introducing a set of principles to keep the conversations around resiliency going. (CSI joined the founding signatories as an ‘amplifier,’ committing to the advancement of the group’s goals. To read the statement, visit aiad8.prod.acquia-sites.com/sites/default/files/2016-05/Res-StatementOnResilience_2.pdf[2].)

The manufacturing community also recognizes advanced materials are helping builders lead in their resiliency plans and goals. Chemical manufacturers are creating and enhancing various ‘ingredients’ that allow structures to better stand up against natural disasters, inclement weather, and the test of time. This article takes a deeper look at some of the latest materials chemical manufacturing companies are developing to increase building resilience.

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Chemistry of insulation
Over the past year, communities of all sizes have been impacted by devastating floods across the United States. Along with immeasurable suffering, these events can also cost billions in damages. (This statistic comes from www.ncdc.noaa.gov/billions/events/US/1980-2017[4]. To read more about floodproofing measures, see the article “Time to Rethink Floodproofing: Recent Floods Have Shown Importance of Deployment Speed,” by Brian Shaw, CFM, in the August 2017 issue of The Construction Specifier.) Where properties are likely to be flooded, particularly in places close to rising sea levels or floodplains, insulation becomes incredibly important.

Certain types of wall insulation are formulated to increase a property’s resilience when faced with uncontrollable natural events. In the event a building is exposed to flood waters, the cavity or solid wall insulation with foam insulation may not be damaged, or will be less likely to need removal or replacement.

Sprayed polyurethane foam (SPF) was created through the work of chemists in the late 1930s. Chemist Otto Bayer, along with his colleagues, pioneered the chemistry of polyisocyanates—a technology used to create polyurethanes. This new material was so versatile it was employed for everything from shoes to cushions to industrial applications (even as a replacement for rubber during World War II). Since then, a variety of monomeric and polymeric isocyanates, polyethers, and acrylics have been introduced for use in the formulation of polyurethane. These components are mixed to form a rigid, cellular foam matrix. The resulting material is an extremely lightweight polymer with high-performing insulating properties.

A wall with sprayfoam has a higher racking strength, or ability to maintain its shape under duress, than a wall assembly without this insulation material. The bond SPF forms to the roof can increase a building’s resistance to wind uplift, which can help reduce damage experienced during periods of high wind. (For more information, check out Canadian Urethane Foam Contractors Association [CUFCA] research online at www.cufca.ca/research/SPF%20Research%20Report-Racking%20Strength-Council%20of%20BC%20Forests.pdf[5].) SPF helps seal as well as conserve energy, serving project teams striving to meet advanced energy codes and contribute toward green building certifications.

With respect to modern residential trends, the phenomenon of tiny homes, micro-apartments, and prefab cottages continues to grow. Even as square footage dwindles, the technology needed to ensure occupants stay warm in cold weather and, in some cases, that homes can be easily moved in the case of severe weather conditions, is increasingly important.

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In commercial applications, continuous exterior insulation solutions that provide thermal insulation, an air barrier, and a water-resistive barrier (WRB) offer many key benefits in terms of a building’s resiliency. For their part, manufacturers, trade associations, and other experts are conducting more in-field performance testing, as well as materials and life cycle studies, to ensure roofing and envelope systems better protect buildings and their occupants during storms and high wind. For example, one chemical manufacturing company utilized its own research and development in SPF in order to have its headquarters become the first property in New Jersey[7] to achieve Double Platinum—the highest certification level for the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program. The company reported no leaks or issues following Hurricane Sandy as a result of its SPF roofing system.

Flex House
Recent innovative building material techniques can be seen in the Flex House by Shelter Dynamics—a modular home built to achieve net-zero energy usage and serve as a showcase for products that improve water usage and indoor air quality (IAQ). At less than 71 m² (760 sf), the Flex House[8] is less than half the size of the average home built last year. Its unique curved roof and closed-cell SPF insulation increase its resiliency against weather events.

The proprietary sprayfoam insulation begins as two separate liquid components, expanding approximately 40 times once applied to effectively seal penetrations and gaps in the building envelope. A low exotherm property (i.e. heat goes out) results in more installed R-value with one pass of SPF. The newer generation of sprayfoam insulation is formulated with a blowing agent that has a global warming potential (GWP) of 1. This is a 99 percent reduction in environmental impact over many SPF blowing agents currently used.

In general, applying SPF to a building helps minimize any air and moisture penetration through the building envelope while also reducing energy consumption. It also affords extra flood protection. Closed-cell sprayfoam is a U.S. Federal Emergency Management Agency[9] (FEMA)-accepted flood-resistant material, meaning it is capable of withstanding direct and prolonged contact with floodwater without sustaining significant damage.

In comparison, some standard types of cavity insulation would become waterlogged within the cavity. Under these conditions, when remediating flood damage, these materials can be expensive to remove and the walls take
a lot longer to dry out. The chemistry behind closed-cell SPF allows it to retain molecular integrity and have low moisture absorption. The material’s use can make repairs considerably easier, less costly, and quicker to complete, enabling occupants to move back into their living or working spaces much sooner.

In severe weather or coastal climate zones, some cavity insulation materials may not be an option as the building’s exposure ratings may make them unsuitable. However, polyurethane foam’s moisture and vapor impermeability, combined with its superior resistance to heat transfer, make SPF products appropriate for multiple climate zones. In the Flex House example, Shelter Dynamics worked with the insulation manufacturer to ensure replicable results for future factory-built net-zero residential projects. The density and high adhesion of closed-cell sprayfoam help maintain the structural integrity of the house when transported to locations ranging from designated residential sites to rural wilderness areas.

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Chemistry of vegetated roofing
Examples of extensive vegetated roof projects can be found in all climate zones. Cities like Los Angeles and Toronto are now requiring these assemblies as a percentage of the total roof space. With careful plant selection, sufficient drainage, and adequate structural support, vegetated roofs can be resilient against ice buildup in winter and droughts in summer. These systems conserve energy, mitigate urban heat island effects, and prolong the overall service life of roofing materials to provide greater thermal comfort during natural disasters or power outages. An extensive vegetated roof requires materials with high compressive strength for loadbearing, as well as long-term protection of waterproof layers.

An insulation material buoyed by chemistry advancements can be critical for such assemblies. NIBS’ Whole Building Design Guide suggests the following in the 2016 update of its “Extensive Vegetative Roofs Design Recommendations[11]:”

The safest route is to locate the insulation above the waterproofing membrane in a protected roof membrane (PRM) or inverted roof membrane assembly (IRMA).

In an inverted roof, insulation is placed atop the membrane, enabling an ideal foundation for a terrace, garden, or vegetated roof on the top of a building. Extruded polystyrene (XPS) insulation is often used as a layer in an IRMA as it does not absorb water. Chemically, XPS foam is a rigid insulation formed with the polystyrene polymer. It starts with solid polystyrene crystals extracted from oil; the extrusion of foamed polystyrene results in a hardened, strengthened material with uniformly small, closed cells and a smooth surface ‘skin.’

In terms of resiliency, polystyrene’s chemistry gives it high resistance to all forms of moisture, such as rain, snow, frost, and water vapor. These properties help XPS create an airtight building envelope that is durable under different conditions. Part of the perspective of resiliency includes preparing for the unexpected. An airtight building envelope with high thermal performance can enable occupants to withstand extended power outages and maintain normal interior climate temperatures longer with high thermal performance.

The special nature of IRMAs in vegetated roofing means insulation
must be assessed for any effects of water absorption by diffusion and freeze/thaw cycles. Tests on XPS materials have shown even after 300 cycles of freezing and thawing, water pickup by this mechanism is less than one percent by volume. The material can also be formulated to achieve other specific attributes, including single extruded thicknesses up to 200 mm (8 in.) and different edge treatments. XPS’ unique chemistry makes it lightweight and easy to fabricate into various sizes and shapes for meeting specific design needs.

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Giant’s Causeway visitor center
A new visitor center at the Giant’s Causeway, a designated UNESCO[13] World Heritage Site in Northern Ireland, displays how polystyrene chemistry can be used for two important building objectives—sustainability and resiliency. Designed by Dublin-based firm heneghen peng, the facility’s vegetated roof offers panoramic views of the scenic Antrim coastline. The geometry of the cast-in-situ reinforced concrete roof contains varying slopes, angles, and fold lines onto which the IRMA was placed, helping to restore the natural ridgeline of the surrounding landscape while also enabling the structure to blend into its surroundings. In the future, indigenous grasses and wildflowers will naturally take root and cover the roof. The vegetated roof also allows rainwater harvesting that, in turn, reduces surface water runoff. The rainwater and greywater recovery from the roof is then routed through a recycling system, allowing it to be used for toilet flushing and roof irrigation.

An XPS product specifically designed for roofs was used to provide durable, moisture-resistant insulation to support thermal efficiency demands, as well as growth of delicate ecology in the area. Such boards have low susceptibility to rot, meaning mold and fungal growth is minimized. Further, the material has shiplapped edges offering interlock between boards, helping prevent thermal bridging and acting against wind uplift—particularly important in exposed conditions such as coastal Ireland.

The material also provides support for drainage layers and growth mediums or soil substrates on vegetated roofs due to its compressive strength sustaining high design loads. Inverted roof insulation must withstand constant loadings from ballast material, for example, without suffering substantial alterations to thickness that could affect thermal performance. The closed-cell structure of XPS gives the material its mechanical strength and a design load of 130 kN/m² (2700 psf), with a maximum deflection of two percent over 50 years. Declaring the design load of insulation products allows specification against the building’s long-term requirements. The design load offers an indication of a material’s mechanical strength over a building’s expected lifetime—an important metric when it comes to quantifying resiliency.

Chemistry of polycarbonate
In 1953, chemists synthesized a viscous substance that hardened inside a beaker. Despite these chemists’ best efforts, the substance could not be broken or destroyed. Today, this high-impact material is called polycarbonate—a type of plastic known for its resistance to cracking and breaking, as well as for allowing the internal transmission of light nearly in the same capacity as glass.

Since its creation, polycarbonate has been used in a variety of applications, ranging from lenses for glasses or goggles to medical devices. The material’s toughness is useful when impact resistance and/or transparency are specified or required in a product, such as the sheeting used to create bulletproof glass.

A transparent, amorphous thermoplastic, polycarbonate sheet can be made in various colors and as translucent or opaque. Its applications include vertical or overhead glazing, as well as canopies, façades, security windows, shelters, and skylights. Thin, ultraviolet (UV)-resistant coatings can be applied to polycarbonate when it is extruded, offering enhanced protection for both performance and aesthetics.

The material’s chemistry makes it resilient to impact and to damaging weather conditions such as strong UV rays or hail. Polycarbonate panels were among the first window glazing materials certified under Florida’s Miami-Dade County building codes. In lab settings, hurricane-tested polycarbonate storm panel windows can successfully resist the impact of a 2.4-m (8-ft) long 2×4 fired from an air cannon at 55 km/h (34 mph). In another test of panel strength, a polycarbonate barrel-vault skylight was impact load and high-pressure tested to 19,727 Pa (412 psf)—the equivalent to 571-km/h (355-mph) winds.

Improved technology in cellular polycarbonate has led to new polycarbonate panel profiles, which are wider, thicker (ranging from 6 to 41 mm [0.25 to 1.6 in.]), and have as many as seven polycarbonate cells (eight walls).

In addition to impact resistance, polycarbonate panels offer opportunities for daylighting—a key component of sustainable building. Daylighting strategies can allow a building to operate without electrical lighting for 91 percent of the annual daytime office hours. U-values as low as 0.16 can be achieved through cellular polycarbonate panel systems comprising double-panels with an air space between the sheets. The material can also be recycled after use or simply reused.

In addition to windows and glazing, polycarbonate can be used as a primary material for a resilient structure. Terrorism, crime, and natural disasters such as hurricanes have led to increased demand for high-performing materials in evolving spaces—particularly where people do business, travel, and gather in large crowds. Polycarbonate sheets with hard-surface coatings, on one or two sides, offer a high level of resistance to abrasion, graffiti, and weathering in infrastructure projects like airports, rail stations, and metro rails. These sheets are also capable of bearing significant weight and wind loads up to 225 km/h (140 mph).

For example, the Shanghai South Railway station, which represents one of the largest buildings with polycarbonate sheets ever constructed, was updated with 55,000 m² (592,015 sf) of tailor-made sheeting to increase the railway’s resiliency and durability. Much of the polycarbonate roof of the station covers the upper departure area, which is around 300 m (984 ft) in diameter and capable of holding up to 10,000 people.

Polycarbonate laminate sheets have also been engineered to help defend buildings—and their occupants—against ballistics impact, forced entry, and bomb blasts. Modern polycarbonate laminates may withstand both physical attack and gunfire from weapons ranging from 9-mm handguns to 7.62-mm NATO high-power rifles, giving more resiliency to construction projects that include embassies, government buildings, and corporate headquarters.

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ICEhouse
A recent project spearheaded by architect William McDonough is one example of polycarbonate’s applications. Earlier this year, his team’s glacial-reminiscent ICEhouse[15] (i.e. Innovation for the Circular Economy) took center stage at the World Economic Forum in Davos, Switzerland, housing some of the planet’s most influential leaders. According to its creators, ICEhouse is designed to illustrate the value provided by robust technical ‘nutrients,’ or materials, such as polycarbonate, in combination with advanced architectural design.

The ICEhouse is primarily made of an aluminum frame structure and several forms of polycarbonate sheets for the cladding. This material is also filled with nanogel[16]—synthetic polymers or biopolymers that are chemically or physically crosslinked—to aid in energy efficiency, which gives the building up to 50 percent energy savings compared to monolayer glass. The ICEhouse’s materials are assembled in ways that allow them to be easily disassembled and reused in another location. In fact, at the World Economic Forum, the walls and roof of the structure were assembled onsite by a crew of four workers in just a few days; the entire structure was completed in nine days.

With polycarbonate as a primary material, the project also has built-in resistance to damaging weather wherever it goes. The sheets are 250 times more impact-resistant than glass and virtually unbreakable; they are tested to perform from −40 to 120 C (−40 to 240 F) even in more extreme weather such as windstorms, hail, or snowstorms. The UV-resistant surfaces prevent penetration of both long-wave (UVA) and short-wave (UVB) sunlight radiation.

The ICEhouse also shows how innovative materials from chemical manufacturers can evolve in new ways to support sustainability philosophies. McDonough is one of the founders of Cradle to Cradle, a biomimetic approach that calls on designs to conserve materials and energy through products that are inherently recoverable, reusable, and recyclable. All the materials used in the ICEhouse either have been certified by Cradle to Cradle or are in the process of certification.

Chemistry of sealants
A structure’s resiliency often depends on the ability to create a strong seal throughout the building’s envelope. Without this, a structure loses its airtightness and watertightness. Building sealants provide important protection to any structure by performing three basic, essential functions: stick, flex, and persist. The first sealants come from humble beginnings, having originated 36,000 years ago in wall construction for dwellings in ancient Babylon and Jericho as naturally occurring bitumen (a type of asphalt).

Sealants in exterior joints are critical for resiliency, guarding against the passage of air and moisture into a building. This is important in maintaining occupant comfort and safety—for example, in the event of power outages during hurricanes in the south or blizzards in the northeast. Such extreme weather conditions can result in bulk water or moisture-laden air harmful to a building’s occupants, contents, and structural components.

Through experimentation and testing of a wide range of chemistries, chemists and materials scientists have developed sealants to meet resiliency goals for specifiers and builders. For example, newer hybrid sealants based on silyl-terminated polyether and polyurethane (STPe and STPu) chemistry are among the latest innovations in joint sealants. They have molecular chains (silyl) that, when modified, exhibit attributes of both urethane and silicone sealants, combining some of the strengths of each.

Both STPe and STPu sealants’ chemistries share many commonalities. The former tend to be lower-modulus sealants, making them ideal for exterior insulation and finish system (EIFS) applications, while the latter are usually higher modulus than STPe, but lower than polyurethane. There is a place for both technologies in the market, depending on the performance demands of joint configuration.

Although they provide different benefits, sealants enable adherence to difficult substrates while providing high movement capability, resulting in long-lasting, watertight seals. Introduced to the North American market in the 1990s, hybrid sealants are considered to be the fastest-growing chemistry within the sealant product segment. In addition to STPu and STPe, a broad range of additives can be also incorporated into hybrid systems. Additional chemistry-based additives can give sealants the ability to bond properly in cold weather, allowing for the construction cycle to be extended and maintenance to be done in winter. The various formulations of sealants also allow for fine-tuning other variables, such as viscosity, UV and color stability, and shelf life.

In addition to STPe and STPu chemistries, SPF can be used as a resilient sealant material. These sealant foams are similar in content to wall foams, and are either single-component or plural-component sealants in cans for smaller cracks and finer applications. Foam sealants help reduce air leakage, which can result in lower utility bills, lowered greenhouse gas (GHG) emissions, and improved IAQ by decreasing infiltration of dust and allergens. (This information comes from www.sweets.construction.com/swts_content_files/153465/2297521.pdf[17].)

Foam sealants can also improve a building’s strength, essentially increasing the resistance to wind uplift in Category IV or V hurricane conditions. Testing at the University of Florida indicates closed-cell sprayfoam[18] used as an adhesive can increase a roof’s wind uplift resistance two to three times that of a typical roof. Testing at Clemson University’s Civil Engineering Department showed foam adhesive systems[19] can increase metal roof uplift resistance 250 to 300 percent versus traditional methods.

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Dayton Towers
The resiliency-focused restoration of New York City’s Dayton Towers, a cooperative of seven 12-story buildings, took place in 2013. Established in 1964 to provide affordable options for middle-income residents as part of the Department of Housing Preservation and Development’s (HPD’s) Mitchell Lama program, Dayton is among the oldest and largest housing cooperatives in the city.

Unfortunately, the advanced age of the structure and years of exposure to salt-laden sea air created conditions in the buildings causing balconies and window seals to leak. This resulted in the corrosion of the reinforcing steel and created unsafe conditions. Adding to the complexity of the restoration project was the extensive 16,722 m² (180,000 sf) of balconies spanning across all seven buildings, requiring major concrete repairs.

The renovation was further complicated by Hurricane Sandy, which impacted all aspects of the project, but also reinforced the need for longer-term protection for changing climates. The versatility of a hybrid seal with strong, primerless adhesion to the broadest range of substrates allowed the project to be completed and the building to be restored for the residents. Hybrid sealants were used on the metal-to-masonry window perimeter joints, offering long-lasting protection from harsh environmental conditions. Their versatility allowed contractors to utilize one sealant for the entire project without the need to switch between products.

Conclusion
Whether it is this article’s examples or other building materials such as flexible piping, wind-resistant roofing, laminated glass, and projectile-resistant doors, the chemical industry will continue to innovate materials for resilient architecture and design.  (To learn more about how materials are built to perform with chemical ingredients, visit the American Chemistry Council site, www.BuildingwithChemistry.org[21].)

(The following contributed to this article: Carrie Stallwitz, Assoc. AIA (building products communications consultant), Gary Parsons, CSI [research and development fellow with Dow Building and Construction], and Christopher J. Perego [marketing manager at BASF].)

Todd Sims is the director of value chain outreach at the American Chemistry Council (ACC), where he manages outreach to the building and construction sector in support of safe, efficient, sustainable, and resilient buildings. An active member of the High-performance Building Caucus, Sims worked previously at the Institute for Market Transformation (IMT), where he developed building energy policies; he also represented the 56 governor-designated state energy officers’ interests in all matters of building energy policies before the federal government, industry stakeholders, and the utility sector at the National Association of State Energy Officials (NASEO). Sims can be reached via e-mail at todd_sims@americanchemistry.com[22].

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