Alternative Construction Methods
- By Thomas G. Dolan
- 05/01/11
When concrete is used as the primary building material for a school, the traditional method has been concrete masonry — blocks of concrete stacked together with mortar, sometimes reinforced and grouted for added strength. But there are also a number of other ways to use concrete and other substances that some claim are faster, with lower costs and more flexibility. The most notable of these are insulated concrete forms (ICF), precast construction, tilt-up, cast-in-place and autoclaved aerated concrete (AAC).
"In general we promote concrete for school construction for durability and longevity," says Jamie Farny, market manager/buildings, Portland Cement Association, Skokie, Ill. "We also think that concrete's thermal mass combined with insulation provides for good energy efficiency."
Ferny acknowledges that concrete may not be considered as green as wood, but says that concrete is made up of materials that are abundant and is recyclable. "There are a lot of ways to tell the sustainability story," he says. "Most energy is lost in heating and cooling. Wood is not a good insulator. It has to be insulated quite heavily, and is not typically energy-efficient in the long run. In steel framing, the steel conducts the heat or cold, so also requires a lot of insulation and good detailing to protect against energy loss. Concrete also transmits heat or cold, but much more slowly."
Here are some of the alternatives to traditional concrete masonry.
ICF
Insulated concrete forms (ICF) consist of two panels of expanded polystyrene (EPS) or extruded polystyrene (XPS) and are connected by a web that is molded into the form that provides an attachment point for interior and exterior finishes. The webs act like a stud in a wood wall. The forms are then stacked similar to masonry blocks, steel reinforced and then filled with concrete. A variety of form types are available — assembled forms, fully assembled forms that fold (which reduces shipping costs) and panelized systems that require assembly on site. The concrete wall has a layer of insulation on both inside and out, on which you can apply a variety of finishes, for both aesthetics and durability. For educational facilities, high impact drywall or a hard coat product is applied for maximum durability on interior walls. The advantage of an ICF structure is that you have a very high insulation value, reinforced concrete walls that can withstand up to a 250 mph wind and the walls are both air- and moisture-tight which create a healthier learning and working environment. With ICF forms, the installation does not require the use of cranes or other heavy machinery. Forms are easily moved around the site by hand if need be. The only heavy equipment required is the concrete truck and pump for the concrete.
Precast
Precast construction is done at the factory. The panels are typically cast as "sandwiches," so that there is a space for both interior and exterior insulation between them. Since these products are made in the factory, not outside at the jobsite and subject to all of the variations of weather and laborers constructing the panels, the quality control is very good. Often, the identical-size panels are made in repetition. They are then trucked to the site and put into place. There can be a cost factor if the panels have to be shipped a long distance. Some say the panels can be large and unwieldy to erect and connect at the site, but others who have used this method have not seemed concerned. Again, any kind of finish can be applied on both the interior and exterior faces.
Tilt-Up
Tilt-up is similar to precast but is done not at the factory, but the construction site.
This means it can be cast horizontally. Then, after the curing and hardening the panels are stood up to construct a wall. Some claim it is easier, in that there is less form work to be done, and you don't have to ship it. On the other hand, you're casting outside, with all of the weather and other variables, a fact that needs to be considered in certain areas of the country.
Cast-in-Place
Cast-in-place, as it sounds, means you go to the site, place the formwork and pour the concrete inside with reinforcement. You can put the insulation on at the beginning of the process or place it on the wall once erected. You can put any kind of finish on it. Some say the downside is it's very labor intensive.
AAC
Autoclaved aerated concrete (AAC) is similar to masonry in that the blocks are stacked and mortared together, although panelized versions are also available. The advantages are a very light-weight, easy-to-place and highly insulated wall. It's a specialized product, pioneered in Germany and popular in Europe. But it's never quite gained a foothold in this country. That can be a disadvantage. It may not be available, may have to be shipped in from afar and may not be supported like the domestic products.
A Closer Look
What makes the ICF system of Nudura Corporation unique, says commercial account representative, Martin Clark, is its six building steps incorporated into a single product. NUDURA forms offer the form system, wall structure, insulation, air barrier, vapor barrier and provide interior and exterior finish anchorage. Clark says that this system reduces what would usually be the three different trades working on the site into one, speeding up the building process by up to 25 to 50 percent. The building envelope, incorporating both the walls and the ceiling, keeps out noise, provides energy efficiency up to 50- to 70-percent of most building scenarios, and can resist winds up to 250 mph.
The Midland, Va.-based Easi-Set WorldWide, offers five different product lines, all proprietary in some way, to a wide range of constructions, all precast and pre-engineered. What's unique to Easi-Set, is that it offers both a floor and a ceiling as well. "Our precast floor systems are in the form of specially prepared gravel or stone foundations," says managing director, Moffette Tharpe. "Our clear-standing roof systems are concrete, with the panels connected together at the site, which can go out to 200 feet," he adds. Membranes are not required for the roof, for it's waterproofed by design, Tharpe says, "and it's very low maintenance."
Brick, stone, or any other finish can be done with foam liners, whether adding school classrooms or adding a new building, so the match with the existing environment is complete. "Versus a site-built building, with all the different trades, weather and cranes, which can take months, our building can be assembled in a week," Tharpe says.
John Lieffrig, regional vice president of the Berwyn, Pa.-based ModSpace, says that modular has a stigma attached. The common misconception of modular is the rickety backlot wooden structure put up to accommodate the overflow of overcrowded classrooms, and not designed to last.
But, he explains, ModSpace has built permanent facilities ranging from hospitals to 24-story-high structures. "Modular is simply a construction process in which a building is constructed, in sections, in a controlled environment, and delivered on flatbed to the site and put together. The pieces have already been pre-engineered to fit together, much like a Lego set," Lieffrig says.
Though it's true that there are elements of “modular” in some of the other methods, such as precast, in this system it is complete. Additions or buildings can, in fact, be temporary or permanent. Modular can have an exterior that will make it fit in with the other buildings on campus. "You're using the same materials as you do in regular construction. It's a difference in process," Lieffrig says. "But the neat part is that in addition to having the structure made in a quality-controlled environment, there is the flexibility and speed. With modular there can be up to 40 percent less wait time."
Case Study
Richardsville Elementary School
The Richardsville Elementary School in Bowling Green, Ky., which was recognized for its Green Design Concept in this magazine’s 2008 Green Education Design Showcase, opened in fall, 2010. This 550 student, 81,000-square-foot, two-story facility is the culmination of 20 years of Kentucky's pioneering for more energy-efficient schools. There are now 257 Kentucky schools with geothermal installations. Built with NUDURA ICF forms, Richardsville has achieved the designation of being the first "net-zero" public school building in Kentucky. In a nutshell, net zero means no overall energy consumption and zero annual carbon emissions. Even though some energy is used in specific situations, the facility produces enough energy to power itself daily. Richardsville does this with its solar energy panels (over 40,000-square-feet mounted on rooftop and support structures), which offset the electricity it takes from the grid. The building will have reduced energy consumption by 75 percent.
In theory, any building can be net-zero, just by loading it with solar photovolaics that generate electricity. But this is cost prohibitive. The difference here is that the building envelope is highly energy-efficient, along with a highly efficient geothermal HVAC system, making big, energy-efficient impacts.
The energy strategies pursued were designed to work in harmony with many of the LEED requirements, enabling the design team to pursue Platinum certification, and set a new standard for public education facilities.