A house’s ability to stand up to the elements, whether it be to hurricane-force winds, floodwaters, earthquakes, or wildfires, is of paramount importance to homeowners. Concerns surrounding the elements are likely only to grow as recent news cycles have been inundated with occurrences of damage related to hurricanes, wildfires, flooding, and other extreme weather events. The material choices made in the building process can help inform the structure's resilience.
While wood framing remains the most common method for single-family construction—94% of new homes completed in 2022 were wood-framed, according to Census Bureau data—alternative materials, including concrete, steel, and even natural-fiber hemp, are available on the market and offer the opportunity to achieve resilient structures.
The share of concrete-framed single-family homes completed in 2022 was 6%, according to the Census Bureau, declining from a 10% market share as recently as 2019. According to an NAHB analysis of Census Bureau data, concrete-framed homes were most prominent in the South, due to residential resiliency requirements.
According to the National Ready Mixed Concrete Association (NRMCA), concrete and insulated concrete forms (ICFs) offer improved resilience, sustainability, and ease of use relative to other construction materials. Gregg Lewis, chief communication officer at the NRMCA, says mass walls, including walls made from concrete, offer superior building performance compared with cavity walls.
“When you build exterior walls with concrete and ICFs, you get not only the thermal insulation and the dramatic reduction of air infiltration, you also get thermal mass, which keeps the temperature differential from migrating through the exterior wall,” says Lewis. “From a construction standpoint, you get the trifecta of the best things that you want for building performance.”
ICFs are a leave-in-place concrete forming system with the appearance of Lego blocks that snap together. Because the form is not stripped after the concrete cures, ICF offers additional advantages by becoming a layer of insulation for the subsequent structure. The ICF also serves as the attachment system for both interior and exterior finishes and offers labor-saving advantages requiring no nail gun or swinging hammers.
“ICF from a concrete industry perspective is the most cost-effective way to get concrete into the walls of a building. It also benefits everybody because the concrete that gets placed in an ICF system gets an ideal curing environment for the concrete,” Lewis says. “Your concrete is actually stronger once it cures in that ICF system versus a traditional forming system because it slows down the process of hydration and the concrete gets stronger over time.”
Lewis says a concrete and ICF exterior envelope can withstand 250-mph wind loads, making the material advantageous in the Southeast, the Gulf Coast, and hurricane-prone areas of the country. The material also dries more quickly than wood or an organic material, reducing issues related to rot or mold in cases of heavy rainfall or flooding, he adds. ICF construction has also become a popular material in fire-prone regions due to its strong fire-resistance performance. While wood typically combusts at 375 degrees Fahrenheit, concrete can withstand temperatures over 1,000 degrees, according to Build With Strength, a coalition of the NRMCA.
With the increasing occurrence of extreme weather events, Lewis says it is becoming increasingly expensive to not build resilient construction.
“If you’re building with an ICF wall system, you’re ultimately building something that is superior from flooding or high winds or fire; you are also getting something that is going to dramatically lower the expense to keep the home comfortable during the extreme temperatures of summer or winter depending on where you are in the country,” Lewis says.
Awareness, resistance to changing building systems, and cost hesitations are among the hurdles limiting a more widespread adoption of concrete building techniques. However, Lewis says the cost differential between concrete and wood is within a few percentage points and that concrete offers sustainability advantages due to the local nature of sourcing. He says the material is extremely efficient, citing an NRMCA partnership with Habitat for Humanity where more than 76 homes have either been started or completed with volunteer labor.
“After [builders] have the first couple builds under their belts, I think they would recognize the benefits and the efficiencies of building a wall using these large EPS foam blocks and placing the concrete in the wall cavity,” Lewis says. “It’s just something that the building industry as a whole hasn’t really latched on to.”
Lewis says wider adoption could be encouraged with the presence of more incentives for builders and building codes.
“I think an awareness of the need for resilience is picking up steam,” Lewis says. “We just hope it’s picking up as fast as it needs to so we don’t have to see more of these disasters where we build and rebuild the same way afterand recognize that there is a way to improve what we’ve done in terms of keeping people safe.”
While relatively new on the market compared with more traditional building materials, hemp-based or natural fiber building materials offer the opportunity to construct both sustainable and resilient homes. Two hemp-product manufacturers, Mr. Hemp House and Hempitecture, exhibited on the National Mall in Washington, D.C., at the 2023 Innovative Housing Showcase in an attempt to educate about the benefits of building with hemp.
Christopher Penn, founder of Mr. Hemp House, says in addition to challenges related to market competition, aesthetic preferences, and cost, hemp-based materials also face hurdles related to skill specialization necessary to use the materials and building code and regulation limitations in certain regions of the country. However, Penn says building with natural fibers, including hemp, provides sustainability, energy efficiency, indoor air quality, and resilient benefits to homeowners. Mr. Hemp House’s flagship product, GaiaCrete, is a bio-based material that can be cast-in-place, made into blocks, bricks, and panels, and into an array of trims, moldings, and casings.
“GaiaCrete shows extreme resiliency to rot, mold, and pests. When they get wet, they dry out,” Penn says. “Over time, they become calcified due to the absorption of H2O and carbon out of the outdoor and indoor environments. The longer [it is in] use, the stronger they get. Of course, all is dependent on the binders used with natural fibers, i.e., hemp hurds.”
Penn says GaiaCrete also has a “remarkable” ability to resist fire, as it becomes harder and more durable over time as it mineralizes. Penn says GaiaCret and hempcrete can delay the spread of flames and reduce the severity of damage due to the use of flame retardants in the composition of the building material.
“It is important to note that the effectiveness of these materials in disaster resistance depends on various factors, including construction techniques, local building codes, and the severity of the natural event,” Penn says. “Building with natural fiber products alone does not guarantee complete protection, but when used in conjunction with proper design and engineering practices, they can contribute significantly to resilience.”
In addition to flood, moisture, and fire resistance, Penn says natural fiber materials also provide resilience and building performance benefits in humid and hot climates, earthquake-prone zones, and extreme cold climates. GaiaCrete and hempcrete have the ability to regulate humidity levels, and the material’s breathable nature prevents mold and mildew growth typically associated with humid climates. The material’s insulation properties are beneficial in colder regions, reducing the energy required for heating and preventing cold air from penetrating the structure.
“The lightweight nature of GaiaCrete, hempcrete, and similar materials can be beneficial in regions prone to earthquakes,” Penn says. “Lighter buildings are less likely to suffer extensive structural damage during seismic activity, enhancing safety.”
Penn says hempcrete structures have “a significantly longer lifespan compared to some conventional materials.” Natural fiber materials also offer improved thermal performance and insulation properties, contributing to energy-efficiency benefits in addition to building performance benefits.
“Both GaiaCrete and hempcrete offer unique advantages in terms of sustainability, insulation, and indoor air quality when compared to traditional building materials,” Penn says. “While they may have slightly higher upfront costs and require specialized installation techniques, their long-term benefits, such as energy savings and improved living conditions, make them attractive options for those seeking environmentally friendly and health-conscious building solutions.”
Penn says additional workshops, seminars, and certification courses for the material and installation techniques can help increase market penetration for hemp building techniques and materials.
The penetration of steel-framed homes in the United States was limited in 2022. According to Census Bureau data, less than half a percent of completed homes framed used steel. Adoption was concentrated in the South (two-thirds of steel-framed homes completed) and the West (one-third), according to an analysis by the NAHB. According to research from the Home Innovations Research Labs, cold-formed steel has seen an increase in adoption in California and Hawaii, areas where earthquakes, fires, winds, and termites present challenges for the resilience of structures.
According to the Steel Framing Industry Association (SFIA), steel, including cold-formed, light-gauge steel framing, contributes to shorter construction times, safer structures, and lower material costs. The material does not rot, split, or absorb moisture and is resistant to pests and termites, both advantages over wood according to the association.
A paper published by the SFIA highlights cold-formed steel structures' performance in adherence with resilience standards laid out by the Department of Homeland Security and the National Institute of Building Sciences. Cold-formed steel is recognized by building codes as noncombustible, making the material eligible for use in Type I buildings where the fire-resistance standards are most stringent.
According to the American Iron and Steel Institute (AISI), cold-formed steel can be installed to withstand seismic categories and wind speeds up to 150 mph. Steel offers an advantage, as the material has the ability to bend or stretch without breaking when a force is applied, unlike other materials used for framing structures.
SFIA says steel is also a moisture-resistant framing material, making it resistant to the formation of mold, and a corrosion-resistant coating on cold-formed steel effectively protects the material from water.
“Cold-formed steel partitions can easily be removed, reused, and/or recycled during building modifications due to its light weight, fire resistance, and flexibility,” the SFIA wrote in Cold-formed Steel and Resilience. “Unlike wood, steel does not increase fire risks when exposed during alterations to a building.”