As the founder and president of Concrete Express Inc. (CONEX), a Georgia ready-mixed concrete producer, David Howard had long dreamed of providing an innovative yet attractive and functional home with his favorite building product—concrete. His dream took shape when he met William H. Harrison, an architect and longtime concrete enthusiast who had been selected by the Portland Cement Association to design its 2001 concrete show house, “Safe Haven,” featured during the International Builders Show in Atlanta.
In mid-2004, the Harrison and Howard teams began planning a house to be built on a secluded site along a
tidal creek near the Intracoastal Waterway between Savannah and Wilmington Island, Ga. The future owner had three goals:
- An appealing contemporary look offering lots of open space and big windows for viewing the marshland and tidal creeks surrounding the property.
- A structure strong enough to survive occasional high-tide flooding and the rare but inescapable 100-mph hurricane. Howard wanted to show that a good plan and the safety concrete provides were affordable.
- Affordability was addressed by adapting standard commercial concrete building materials such as insulating concrete forms (ICFs), masonry blocks, and extruded, pre-stressed decking.
The result is a striking two-story residence with 5600 square feet of living space and 7400 square feet of ground-floor garage, covered porches, and storage space. Designed for a beach and boating lifestyle, the house has guest bedrooms downstairs and a master bedroom suite and office upstairs; a main-level screened porch with a concrete fireplace and an outdoor kitchen; a turret-shaped dining room with a custom cast-in-place concrete-based mahogany table; a living room that opens onto a spiral-shaped, three-tiered swimming pool and spa; and river access via a floating concrete dock.
Devoted to concrete
For Howard, whose company is supplying 1500 yards of concrete for the house, the job offers an ideal opportunity to apply the latest advances in concrete technology to residential construction. Howard, particularly interested in ICFs and self-consolidating concrete (SCC), soon learned that these techniques and materials require more precision and attention to detail than more standard construction methods.
“This was my first experience with ICFs, and I soon learned that bracing and shoring are critical in dealing with light non-structural formwork,” he says. “You cannot skimp.” To provide assistance, the ICF manufacturer, Reward Wall Systems, had a representative on-site periodically.
The second- and third-floor exterior walls are constructed entirely using ICFs. To create window openings, window bucks were secured by tie wire and rebar, with observation holes drilled in the bottom of the sills to allow workers to see when the concrete reached the right level, thus assuring that the forms were completely filled.
SCC was used for the ground-level (garage) walls, but was poured in place using steel forms, not ICFs. The SCC (using Sika's Sikament admixture) allowed the 10-foot-high, 10-inch-thick walls to be poured in a single lift with only minimal movement of the pump.
The garage floor is set 2 feet above grade and constructed on a base of flow-able fill—a combination of sand, fly ash, cement, and water—that guarantees full 2000-psf compaction around the foundation. (Flowable fill can be excavated if necessary and is safer for filling trenches in areas with a high water table.)
Building by example
If recent history is any guide, another direct hit from a large hurricane is only a matter of time. “In the coastal areas and other areas prone to tornadoes and other extreme weather, I believe that over the next 25 years, we will continue to develop much more economical ways to build in concrete,” Howard says.
Back at his computer, Howard reviews house plans and calls up records and resources for each technique used in the structure. Almost on schedule for an early 2006 completion date, he seems pleased with his crew's progress in mastering the new techniques.
“Self-consolidating concrete, already integrated into a lot of commercial and industrial work, now is gradually being integrated into residential work,” he says. “I decided that the best way to educate people about the different aspects of using concrete in a house was just to build a good example.”
Designing for concrete
For Harrison of Harrison Design Associates, with offices in Atlanta and Santa Barbara, designing another East Coast beach house was not unusual. “Often, the form and style of a contemporary house is best executed in concrete,” says Harrison. “You can create just about any design or shape you want. The only limitation is the craftspeople's ability to make the forms.”
Here, Harrison used curved forms, glass, symmetrical openings, and flow-through interior spaces to capitalize on the unique properties of concrete construction. The house's entranceway is a 37-foot-high, 20-foot-diameter concrete and glass greenhouse tower, with a 5-foot-wide circular porthole cutout near the top. Because the living space is set 15 feet above the flood plain, as required by federal building standards in coastal areas, visitors ascend to the main floor by a glass and steel elevator or an elegantly curved stairway.
“Big, open, curved stairways are hard to execute in wood framing, but they work well in concrete,” says Harrison. “You have to coordinate the design with the structural engineering, paying attention to the basic organization of the house.” The team admits the port-hole was a challenge. Like the stairs, the massive, curved, 37-foot wall with its distinctive cutout was poured using SCC.
Getting the right mix
Under the watchful eye of Howard's skilled crew, the SCC yielded a highly workable mix requiring no vibrators to create big sections of smooth, honeycomb-free walls, ideal for creating the dramatic porthole centerpiece where visitors see through the house to the water. Using pre-stressed concrete deck spans for the flooring system had distinct architectural advantages, too. The hollow-core, 4-foot-wide concrete deck panels are 8 inches thick and can span up to 40 feet. “The large spans allowed us to create lots of clear, open spaces,” Harrison explains.
Concrete construction contributes integral structural benefits often seen as desirable but expensive add-ons in conventional wood frame construction: high R-value insulation, soundproofing, fireproofing, and exceptional durability. “Concrete gives you a structure that's dimensionally stable and also fireproof,” Harrison says. “You don't have the expansion problems you have with wood—the shrinking and moving with moisture—and it's quieter. Because of the density of the materials, there are no vibrations.”
Concrete construction's costs have become competitive with wood in coastal areas, given the increased demands for hurricane resistance. “If you compare structurally equivalent walls at equal wind loads, such as a 100-mph wind resistant wall, concrete is cost-competitive with wood framing,” Howard says.
— Faye Goolrick is a freelance writer based in Atlanta.