Using concrete in buildings today to conserve the future
By William D. Palmer, Jr.
Let’s begin with the things you already know about concrete: Concrete is, of course, strong — at least in compression. And concrete reinforced with steel can handle the worst abuse — we build bomb shelters and prisons with concrete. It doesn’t rot, even under water or in soil. It can be molded into nearly any shape imaginable. (Think Calatrava’s Tenerife Auditorium.)
You may also know that concrete’s thermal mass can contribute to a building’s energy efficiency by reducing interior temperature swings, thereby reducing the size of heating and cooling equipment. It can incorporate recycled material like fly ash and blast furnace slag. And, it’s mold-proof and does not off-gas toxic substances.
On the other hand, you also know that concrete requires formwork that can be expensive, increasing the initial cost of construction. Concrete is more complicated to build with and once in place is difficult to change. Poorly built concrete surfaces are not very attractive and cracking seems inevitable. And it just isn’t warm and inviting like wood.
However, concrete is an essential ingredient of sustainable construction.
Concrete’s greatest contribution to sustainability lies in is its durability. When a concrete building is designed properly, it will perform admirably for many years and will offer its residents energy efficiency and safe shelter from nearly any natural or manmade disaster. And when the end of its life finally does arrive, concrete is eminently recyclable and can even be turned into new concrete by crushing it into aggregate.
But aren’t concrete structures more expensive? The same question is often asked about sustainable construction in general and that, of course, depends on how you measure it. The initial cost for concrete buildings is typically a bit higher than for buildings using other materials. But we all know that is only a small part of the story. The true way to look at the cost of a building is through life cycle assessment, including everything from extracting the raw materials (and reclamation of mine sites) through operating and maintenance expenses until the end of the building’s life. This is where concrete shines, since operating expenses are typically much less for a concrete structure. Consider the Roman Pantheon’s concrete dome, which is still standing after 2000 years. (To learn more about life-cycle costs and concrete, go to ConcreteThinker.org.
In residential construction, concrete’s advantages may be even more pronounced. Energy-efficient, safe concrete homes come in a wide variety of configurations. “The initial cost of a concrete home depends on several variables,” said the PCA’s Jim Niehoff, “especially the experience of the builder with the particular system and part of the country you are building in. In a costal area, for example, you have heightened requirements to meet certain wind loads. You really have to beef up wood frame construction to meet those standards, but you don’t have to do much different with a concrete home. So all of a sudden, concrete is very competitive.”
Even typical cast-in-place concrete construction is air tight and has thermal mass, although without added insulation its R-value is low. Many modern concrete homebuilding techniques, though, incorporate insulation in a variety of ways to result in energy-efficient, quiet, disaster-resistant homes:
Precast panels: Sandwich panels incorporate insulation into the wall cross section. Dukane Precast in the Chicago area, for example, manufactures double-wall panels with 3-1/4 inches of insulation sandwiched between layers of concrete to achieve an R-22 wall.
Insulating concrete forms (ICFs): Once relegated to residential basements, highly energy-efficient ICFs are now also being used for above-grade walls for homes and even for multistory buildings, especially hotels and schools.
Autoclaved aerated concrete (AAC): Blocks and panels made from AAC are lightweight and a 10-inch wall has equivalent R-values in the low 20s.
Tilt-Up: Several systems are in use today to insulate tilt-up panels for homes, including T-Mass from Dow Chemical’s Styrofoam line. The New American Home (TNAH) at this year’s International Builders Show used T-Mass panels (see sidebar) but with plant precast panels rather than site-cast tilt-up panels.
Concrete Masonry: CMU construction can achieve high R-values by injecting foam into the cores. The majority of Florida homes today are built with CMUs.
Sprayed concrete: Several systems have emerged recently where polystyrene insulation is erected and then concrete is applied to both sides by spraying or shotcreting. A recent 9,200-square-foot home in Illinois built with this method has an expected 100-year life.
Concrete’s contribution to sustainable construction doesn’t end with walls. During the past 10 years, we have seen a revolution in decorative concrete, especially for interior floors and countertops. Durable decorative surfaces have many advantages both in commercial and residential construction.
Streets, driveways and parking lots have been concrete for many years, and contribute to sustainability by reducing heat-island effects with their lighter, more reflective surfaces. But pervious concrete takes this one step further, by draining rain and snowmelt directly into the subsurface and eliminating the need for runoff retaining ponds. For more information about pervious concrete, visit the ConcreteAnswers Series for Architects, Engineers and Developers.
One criticism of concrete has always been that cement manufacturing is energy-intensive and produces large quantities of CO2. While at one time those points may have been valid, the cement industry has taken an extremely aggressive approach to reducing these impacts. Start with the fact that today cement manufacturing accounts for only 1.5 percent of U.S. CO2 emissions.
So come along with us to learn why when you think about sustainable construction, the first material that should come to mind is concrete.
The New American Home
Each year at the International Builders Show, sponsored by the National Association of Home Builders (NAHB), a special home is built to showcase the most innovative materials and methods in homebuilding. For six years in a row, including the home built for the 2009 show, concrete has been a primary component of The New American Home. “There’s a nice synergy since they always want to demonstrate cutting edge housing technology and each year that includes concrete,” said the Portland Cement Association’s residential promotion manager, Jim Niehoff.
The 2007 TNAH used insulated precast panels for walls and hollow-core precast planks for floor/ceiling decks. By combining air-tightness and thermal mass, the above-grade walls provide thermal performance equivalent to an R-26 wall. Foundation walls are also precast panels, with exterior R-5 insulation. The cement-based stucco used on much of the home’s exterior incorporates a new photocatalytic cement, TX Active, from Italcementi. Developed initially as a self-cleaning cement, it was soon learned the reaction also consumes carbon monoxide, nitrous oxides, and sulfur dioxide. Italcementi has calculated that coating 15 percent of the exterior wall surfaces in Milan with TX Active would result in a 50 percent reduction in airborne pollutants.
Protecting America’s Homes
Although building codes, especially in coastal regions, are becoming more stringent, the U.S. insurance industry is funding an effort to make buildings even safer. While safer buildings may be good for the insurance industry, they are much better for the people who live in them. The Institute for Business & Home Safety (www.ibhs.org) has developed a program called “Fortified…for Safer Living” to develop guidelines that will minimize the property damage homeowners suffer from natural disasters. Fortified program manager Chuck Vance says, “the program is code-plus with independent verification inspection. Any home that meets the Fortified standards will be above the minimum standards if code is in place and quite a bit above local practice in areas where code is not in place.”
To achieve the Fortified seal of approval, a home — regardless of the building material — must be able to demonstrate that it is constructed to better withstand the “perils” it is subject to, whether that be hurricanes, tornadoes, extreme winter weather, wildfire, or flooding. “Every Fortified home must have independent verification by an IBHS-certified inspector that it meets a specific requirement for a given location, which is code-plus, even if they already have a code in place,” said Vance. “We believe these homes will stand up even better than code-designed and built homes. For the homeowner, this means peace of mind and a stronger, safer, more durable home that is more sustainable in the face of the perils in their region.”
Concrete homes are not a requirement of the Fortified program, but there is an advantage.
“The factor that makes concrete a good building material for residential construction,” said Vance, “is that whether it’s block or ICF or poured, it’s reinforced with steel and can withstand the wind loads, and is fire resistant and very durable. So, it’s a little easier to get to a Fortified home using concrete. Those builders that are using concrete residential building techniques tend to be building a stronger better home already and they know it and want to get credit for it.”
Royal Concrete Concepts, a manufacturer of modular concrete homes, was recently recognized by IBHS as a builder of Fortified homes. “All single-family homes offered by Royal Concrete Concepts will receive the Fortified designation when sited according to our qualifying criteria,” said Vance. “By offering affordable homes up to 2,500 square feet, Royal is furthering the Fortified program’s goals to make disaster-resistant housing an option for more people.”
William D. Palmer Jr. is a construction writer and president of Complete Construction Consultants in Lyons, Colo. He was formerly editor in chief of Concrete Construction magazine and executive director of The Masonry Society. He writes a blog that appears regularly on the Concrete Network. This article originally appeared in Environmental Design + Construction magazine.