A ToolBase TechNote
Concrete is vital for the home building industry. Cement or concrete is used in almost every building project, whether new construction or remodeling. Builders are voracious consumers of concrete, using it for footings, foundation slabs, driveways, sidewalks, and even exterior walls. Now, in certain parts of the country, the availability of concrete has been significantly depleted, driving prices up and leaving builders to search for alternatives.
Nationwide, the United States imports about 22 percent (totaling about 23 million metric tons) of the 107.5 million metric tons Portland cement consumption each year. The top exporters of cement to the United States are Canada (about 25 percent), China (about 24 percent), Thailand (about 18 percent), and Greece (about 10 percent), according to the Portland Cement Association (PCA), a trade association based in Skokie, Ill. China's booming economy and its growing domestic demand for raw materials have forced it to curtail its cement exports in recent months. This, coupled with the current construction boom in the United States and overburdened shipping companies, is causing a worldwide shortage of cement, the key ingredient in the manufacture of concrete.
In parts of the country such as Florida, the home construction market is particularly vulnerable to price fluctuations and shortages because it imports about 40 percent of its cement annually. Beginning in the spring of 2004, South Florida home builders began reporting delays in getting concrete deliveries, according to Beth McGee, executive vice president of the Home Builders Association of Metro Orlando. These delays resulted from concrete rationing to builders in the state as concrete producers cut back production due to the cement shortages. The concrete shortage is likely to spread across the Southeast, said George Hossenlopp, president of Florida Concrete & Products Association and president of Jacksonville-based Florida Rock Industries' Southern Concrete Group.
In the midst of the cement shortage, other building materials are also experiencing supply and price fluctuations, making the search for alternatives even more difficult for builders. Michael Carliner, an economist for the National Association of Home Builders (NAHB), said builders also are coping with sharp price increases in lumber, including plywood and oriented-strand board. Framing lumber is up about 60 percent from a year ago, while plywood and oriented strand board have shot up about 200 percent. Steel prices sharply increased over the past six months too, which, while it has been felt more by commercial contractors than home builders, still adds to the overall challenge.
How might these combined factors affect home prices? One builder estimated higher cement prices, coupled with increases in other building materials such as wood, steel, and asphalt, could drive up construction costs for a new home by as much as 5 percent in the near term. That would be $10,000 more in building costs for a $200,000 house.
"This is likely to continue to be a problem, at least until late this year," said Carliner. According to PCA, any supply problems that do occur will be regional, with the length and severity of the shortage depending on the cement companies serving that region. In reality, no one knows how long this problem will last or how high the prices will go. To provide better balance between supply and demand in the future, cement companies have announced plans to expand manufacturing capacity by more than 10 million tons by 2008, a roughly 11 percent increase, according to Ed Sullivan, chief economist for PCA.
Alternative Materials and Construction Methods
With little indication of short-term relief in the cement prices and shortages, what can builders and contractors do to cope with this disruption and continue to run profitable businesses? Alternative materials and construction methods may be the answer. Some of those alternatives are described below.
Wood foundations are load bearing lumber-framed foundation walls sheathed with structural wood sheathing. All lumber and plywood components are pressure-treated to withstand decay from moisture and damage by termites. Southern Pine dimensional lumber is the industry standard for wood foundation construction.
Prescriptive provisions for the construction of wood foundations are in the International Residential Code (IRC). No special design or engineering is required for wood foundations. These types of foundations have been used successfully in thousands of homes and other structures throughout the United States.
Wood foundations are relatively easy to construct and adaptable to various environmental conditions. The work can be done by framing crews under a wider variety of weather conditions, or these foundations can be prefabricated, eliminating the need for a concrete contractor, as no concrete walls have to be poured. Remodelers can readily frame wood foundations for additions, and modifications to existing wood frame foundations are less complicated (and therefore less costly) than for block or concrete structures. Installation of wiring, plumbing, ductwork, insulation, and wall finishes are all very basic with wood framing, and are accomplished with similar techniques as for other framed wall systems. Finishing costs are lower as the wall studding is already in place, which eliminates the need to construct a separate wall inside the foundation for the insulation.
In addition to the simplicity of their construction, wood foundations can provide more living space in basements than houses constructed over masonry or concrete foundations. Below-grade living areas are larger because the interior frame wall required with masonry or concrete foundations can be eliminated. For an average sized house, this can add up to anywhere between 50 to more than 100 square feet of basement living area. The flexibility or elasticity of wood is said to make the foundation structure less susceptible to cracking or shifting, and easier to insulate for improved thermal performance.
Manufacturers have estimated costs for wood foundations to be approximately $45 per foot of 8' wall, which includes foundation coating, 6 mil. polyvapor barrier, and hardware. Costs for wood foundations with non-arsenate formulas may be 10 to 20 percent higher than for those with CCA treatment.
Some may be skeptical about the long-term durability or strength of wood foundations. However, accelerated aging tests, and use for over 40 years in the construction industry, are testaments to the durability of this system. Permanent wood foundations for residences have been constructed for decades in the United States.
For more information on wood foundations, refer to the Technology Inventory listing on the ToolBase portal.
Cold-formed Steel Foundations
Cold-formed steel, or light-gauge steel, has been gaining wider market share because of its many advantages in high-hazard regions and insect infested areas. Its price stability, until recently, has attracted many builders and framers in the Southwest, West Coast, and Hawaii. The Steel Framing Alliance (SFA) reported that over 60 percent of new housing starts in Hawaii today are steel-framed.
The price of steel had gone down over the past three decades due to higher productivity, improvements in steel mills, and the start-up of mini-mills. However, the building boom in China has affected steel prices as it has for other materials. As the Chinese economy has grown, the construction market there has started to consume more steel creating a shortage worldwide. This had caused steel prices to increase by up to 100 percent since summer 2003. Despite these price fluctuations, there are still ways to use steel foundations economically.
While steel foundations are not recognized by the IRC and there are no prescriptive tables for them, they can be used effectively if they are properly designed and installed. A below-grade steel stud is no different than an above-grade steel stud - the below-grade stud is subjected to lateral soil loads, just as the above-grade stud is subjected to lateral wind loads. The designer has to be careful though in selecting the exterior sheathing for steel foundations. Pressure treated wood containing copper is highly corrosive to steel and needs to be isolated from steel members.
For more information on steel foundations, refer to the Technology Inventory listing on the ToolBase portal, or visit the Steel Framing Alliance website.
Frost Protected Shallow Foundations (FPSF)
Frost Protected Shallow Foundations (FPSF) can not only save energy, but slash construction costs as well. The technology itself is nothing new - FPSF have been used in Scandinavia for more than 40 years (where it's now standard practice), and are now becoming more commonplace in the United States. This kind of foundation is most efficient in cold climates, but can be used beneath heated or unheated structures.
In order to protect foundations from frost heaves, most cold-climate building codes require foundation footings to be installed below the frost line, which can be 3 to 6 feet deep in some states. The FPSF concept is simple: Instead of placing footings below the frost line, the FPSF uses insulation and drainage techniques to raise the frost line to just below the surface. Even in the coldest climates, this technique permits footing depths as shallow as 12 inches. "We basically make the footings think they're in Florida," joked Bill Eich, a builder from Spirit Lake Iowa who uses FPSF almost exclusively.
FPSF create a win-win situation for the builder and homeowner. Shallow foundation ditches are easier to work around and therefore, result in less concrete being used (FPSF uses less concrete than a 4-foot deep stem wall), costing the builder less for construction. For example, in a 131-unit Denver, Colo., housing project, the U.S. Department of Housing and Urban Development was able to save $3,000 per unit by substituting traditional stem walls with FPSF. In a 1993 NAHB Research Center demonstration project, the cost of an FPSF was compared to an equivalent slab-on-grade foundation with footings extending to the local design frost depth. Savings with FPSF over standard slab-on-grade foundations varied between $635 and $4,750. The wide range of savings reflected varying local frost depth, and builder overhead and mark-ups. Another study conducted by the NAHB Research Center in 1988, showed a 15 to 21 percent savings with FPSF over conventional foundations. These construction cost savings can be passed along to homebuyers, and they can reap the energy savings that FPSF provide as well.
For more information on frost protected shallow foundations, refer to the Technology Inventory listing.
Insulated Steel Panels (Panelized Steel Foundations)
Panelized steel systems are similar to structural insulated panels. They are fabricated from steel sheet skin (typically 22 gauge thick) and extruded or expanded foam sandwiched between the steel sheets. Other systems consist of steel studs embedded in extruded or expanded foam. The panels are either mechanically interlocked (with fasteners) or welded together. Whichever system is used, the panels can be successfully used as basement or foundations walls.
Cost savings for these foundations come from the ease of installation as work can be done by framing crews under a wide variety of weather conditions. These systems also eliminate the need for a concrete contractor, as poured concrete walls are not needed and footings can be poured without a concrete contractor. A recent time and motion study performed by the NAHB Research Center for the Mid-Atlantic Steel Framing Alliance (MASFA) documented construction time for a single-family home using Premium Steel Building Systems panels. The labor cost for the foundations was $0.18 per square foot of living area. It took 19 labor hours to construct the foundation. The cost of these panels usually comes at a premium, therefore, a builder should look at the total cost rather than the labor cost alone.
Other Wall Panels
There are a variety of panelized systems that combine the strength of steel or other composites with concrete to form wall panels. Tridipanel, for example, produces a prefabricated polystyrene wire mesh panels that becomes a structural wall when concrete, gunnite, Portland cement, plaster, and stucco are shotcreted into place. Tridipanels have been tested to withstand extreme temperatures; they are earthquake tested and use recycled green products. These systems are not always available in all markets, nor do they provide a complete solution. However, when available, these alternative systems can provide an economical alternative to concrete or block walls.