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This is the final installment in a four-part series introducing different forms of systems-built housing and the possibilities that exist when putting these concepts into practice. This issue: concrete building systems.
Builders seeking to employ environmentally sound building techniques while reducing their construction time should consider incorporating one of a variety of concrete construction techniques in use today.
In addition to being affordable, concrete offers builders several other universal advantages:
Green. Concrete building systems enhance green building processes by incorporating a combination of recycled and natural materials.
Predictable. Builders can improve their financial forecasting because the costs of the basic components of concrete — cement, sand, water and aggregate — are more constant than dimensional framing lumber.
Profitable. Concrete building systems can boost a builder’s profitability by increasing the speed of construction, which can lower the risk of job site thefts and comparable insurance costs.
Concrete homes also have few construction limitations and offer home builders and buyers numerous benefits — including ease of construction and maintenance, increased comfort and security, lower energy bills and exceptional durability.
Like other systems-built construction techniques, builders can choose from a variety of concrete construction systems when building homes:
Concrete Masonry Units: The ubiquitous concrete block, also known as a concrete masonry unit (CMU), has been the foundation for much of U.S. housing, as well as for above-grade commercial construction.
But that foundation has gone high-tech and is now vastly improved. With aggregates making CMUs up to 25% lighter, a mason can install more of them in an hour than ever before — reducing labor expenses and construction time. In addition, CMUs are safer and more durable. They don’t burn, melt or warp and are capable of withstanding severe weather, earthquakes, floods and fires.
Insulating Concrete Forms (ICFs): Insulating concrete forms (ICF) are interlocking modular units that are dry-stacked and then filled with poured concrete. The foam form remains in place once the concrete is poured, becoming a permanent part of the wall assembly.
The combination of the form and concrete achieves high R-values, reduces the likelihood of air infiltration and improves thermal mass properties, which can account for substantial energy savings in ICF homes.
In addition, houses built with ICFs are quieter. According to recent sound transmission tests, two-thirds less sound passes through ICF walls than through stick-framed walls filled with fiberglass insulation.
Autoclaved Aerated Concrete: Technically, autoclaved aerated concrete (AAC) systems are blocks held together by mortar. Unlike CMUs, however, AAC is made with a natural expansion agent that creates countless small air pockets and causes the concrete to rise — much like bread dough — which makes AAC systems lightweight and easy to work with onsite.
Among AAC benefits to residential construction: AAC has a high strength-to-weight ratio, making it structurally strong; AAC systems are fire- and insect-resistant; and AAC systems allow for more flexible design options for the entire building envelope — including walls, floors and roof systems.
Precast Concrete: About 60% of existing homes have foundation leaks and between 20% and 30% of a home’s heat loss occurs through the basement. Precast concrete foundation systems are specifically designed to provide a moisture-free and energy-efficient living space that reduces heat loss and the energy loss incurred by foundation leaks.
With precast concrete systems, large wall panels are poured horizontally in a controlled factory setting. Once hardened, the panels are delivered by truck to the job site, hoisted into place with a crane and joined together.
Because precast concrete systems are manufactured well in advance of installation and can be shipped to a job site almost on demand, precise concrete enables quicker enclosure and faster progression.
Removable Concrete Forms (RCFs): Also known as cast-in-place, the removable concrete form system is based on removable or temporary forms similar to the removable forms used to make poured-in-place foundation systems — but on a larger scale.
RCFs are typically made of aluminum or steel that can be used repeatedly to build thousands of concrete homes.
RCF systems fall into two basic categories — modular aluminum forming systems and steel “tunnel” forming systems.
The aluminum systems can be used to construct virtually any building plan because the forms are assembled from basic modules for each home. Tunnel forms typically are manufactured to build a particular plan.
RCFs’ ease of application enables exterior walls, floors, roofs, decks, stairs and interior bearing walls — essentially a total concrete shell — to be built at a faster pace.
With RCFs, interior walls usually are finished with a skim coat of plaster, followed by paint. RCF interior walls are virtually indistinguishable from a drywall finish.
The Concrete Home Building Coalition — part of the NAHB’s Building Systems Councils (BSC) and sponsored by the American Concrete Institute, the National Concrete Masonry Association and the Portland Cement Association — is America’s premier resource for concrete home construction information. For more information, visit www.nahb.org/concrete. Learn more about the various types of residential concrete construction at www.nahb.org/ConcreteVideo.
To learn more about the Concrete Specialization Courses through the Home Builders Institute’s Residential Construction Superintendent Series, visit www.hbi.org/concrete.