Innovative concrete homes: a variety of construction methods are being used

Concrete Construction, April, 2003 by Joe Nasvik, Bill Palmer

Being innovative does not mean just being creative with design. It encompasses all aspects of the construction process. Of the many market applications for concrete homes each takes advantage of different benefits of the material. Many companies are innovating in the construction of concrete homes for very different reasons, as described here.

Doing it the Mercedes way

Vince Heuser is the manager of Solid Wall Systems, a subsidiary of employee-owned Mercedes Homes, Cocoa, Fla. Heuser thinks Florida is the nation's most competitive market for home construction. Therefore, using concrete as the building material--in competition with steel frame, wood frame, and concrete block--is a challenge. In Heuser's world, he must win over a customer to an innovative approach in four areas:

* The home must cost less than one built with other materials.

* The finished product must provide significant energy savings.

* The building must take less time to construct.

* Maintenance expenses must be reduced.

Solid Wall Systems is focusing its activity in central Florida, where its specialty is 1200- to 3500-square-foot homes; in the past 2 years it's completed 500. The company currently constructs exterior concrete shells at the rate of two per day--soon to increase to three per day. Heuser says the concrete homes are less expensive and faster to construct than concrete block homes, so he targets developments that competitively bid the two materials. But in areas where wood frame is the norm, "We can equal the cost of wood frame construction, but that's not enough to get the job," he notes.

Typically, crews erect aluminum forms for the exterior walls and place concrete the same day. They remove the forms the following morning and reassemble them on the next site. Heuser says that they don't build interior concrete walls because they can't compete with the cost or speed of steel stud construction. A crew can complete all the interior walls with steel in one day, so they get the job. Concrete walls would take 2 days.

Solid Wall Systems builds 6-inch-thick concrete walls. Afterward it places 3/4-inch closed-cell foam insulation (R-4) against the inside wall and 3/4-inch furring strips over that, with electrical wiring between the furring strips. Plumbing is located in hollow interior walls. Crews use aluminum buck forms for windows and doors, leaving only a 1/8-inch caulking gap between windows and concrete, producing an airtight structure. Energy savings result from this tightness and from the thermal mass and insulating value of the concrete walls, which absorb heat during the day and release it back to the environment at night--with little heat gain to the interior. Energy savings of 30% over block construction and 50% over wood are common.

"One added advantage we enjoy is locked-in concrete prices for a year," Heuser adds. "Lumber prices are typically adjusted quarterly."

Building in the face of hurricanes

Sue McLaughlin, the planning, zoning, and Coastal Area Management Act (CAMA) officer for North Topsail Beach, N.C., says that Topsail Island has the lowest elevation of all the barrier islands, and more than 375 homes have been destroyed by hurricanes over the past 15 years. The state recently changed the building code requirements in hurricane-prone areas to require all buildings to withstand 130-mile-per-hour wind loads--up from 110 miles per hour. This change doesn't affect the design of a concrete home but necessitates elaborate changes for wood frame buildings.

Security Building Group, Raleigh, N.C., is currently building six duplex vacation homes on North Topsail Beach, about 100 feet from the high-tide line and only 8.5 feet above mean sea level. The floor slab for each home is perched on columns 10 feet above the sand, 4 feet above the base flood elevation.

Dave Pfanmiller, general manager of Security Building Group, said there are 28 caissons per dwelling, installed using the Continuous Flight Auger (CFA) method to a depth of 45 feet. Heavily reinforced grade beams 18x20 inches span the caisons and columns 12x30 inches are located on top of the grade beams, with an 8-inch-thick structural slab cast over the columns. After this, home construction begins.

Tri-City Contractors, Raleigh, N.C., the structural concrete contractor for this project, used aluminum forms to construct all the walls and decks (ceilings). Each home has two floor levels and each entire floor level (all walls and decks) is cast monolithically. Only a truss roof above the second-story attic deck is made from wood.

The homes have a mass adjusted R-value equivalent to 30 and are airtight. Air-to-air exchangers will dehumidify and provide a constant 0.75 air change per hour, compared with the average four to five air changes per hour that leak into the average wood frame home. Pfanmiller feels that these homes will result in up to a 50% energy saving over comparable wood-framed homes.

The most innovative home in America

"This home delivers superior quality any way a homeowner might wish to define it!" So says Jon Rufty, Rufty Homes, Cary, N.C. He should know. He's on the board of directors of the National Association of Home Builders (NAHB) and also on the board of directors of the Sky Blue Foundation, whose goal is to develop safer, disaster-resistant homes with lower insurance rates.