Precast concrete walls stand up to scrutiny
Fast. Efficient. Strong. Precast concrete walls cut building time, offer better insulation and stand up to hurricane winds.
By JUDY STARK, Times Homes and Garden editor
Published October 13, 2007
If you've ever baked a big, thin pan of gingerbread, then cut it into rectangles and stood them up to create the walls of a gingerbread house, you already understand how a precast concrete home is built.
The walls are poured in frames in a factory, with window and door openings cut out. They're taken to the homesite on a flatbed truck and swung into place by cranes, then bolted together.
Maybe you're used to seeing workers building walls out of masonry block at residential construction sites around Tampa Bay. Keep an eye out for those cranes and those swinging walls.
Why? Speed of construction, for one thing. "It can cut about a third off" construction time, says contractor Steven Fernald, who's working on a project in South Pasadena.
Two more reasons cited by Jim Niehoff of the Portland Cement Association outside Chicago: "Energy efficiency and disaster resistance." Those are sweet words in hot and hurricane-prone Florida. A precast home, Niehoff says, "is a veritable fortress."
A time saver
Verne Packer stood in the garage of one of the townhomes he's building off Pasadena Avenue in south Pinellas. The exterior walls are made of precast concrete, 5 inches thick and two stories tall, with 3/4-inch rigid foam insulation and 5/8-inch drywall on the inside.
"This building went up in four days," he said, referring to the three-unit building, one of seven that will be the Villas at Date Palm. With masonry-block construction that would have taken three weeks, he said. "These walls have a wind rating of 295 mph."
He pointed out the steel corner plates that tie the wall panels into the floor joists and roof trusses.
Inside, he gestured to the windows and glass doors. "We installed all the windows in this three-unit building in one day," he said. "We can cut three weeks out of the construction schedule." In an industry in which time is money, that's significant.
To "dry in" the building - walls, trusses, roofing, interior framing, windows and doors - took three weeks, a task he estimated would take six to seven weeks with masonry construction.
The concrete panels reduce sound transmission from one unit to another and have a two-hour firewall rating. The walls have an energy rating of R-18 to R-20. The code-required minimum is R-13.
Natural disasters, pressure from the insurance industry, changing building codes, consumer demand for safer, more energy-efficient homes - "all this pushes us more and more toward production materials and designs that sustain human life and reduce damage," said Brian Miller of the Precast/Prestressed Concrete Institute in Chicago. "Precast is one of the best materials and building systems to do this."
A similar system has been used for years in commercial construction. Highways, bridges and parking garages are common precast projects. Precast is common in residential construction in Europe.
Industry experts enumerated these benefits of precast construction:
- Less onsite construction waste.
- No need for a materials staging area, scaffolding or a large work area.
- No weather delays.
- No need to protect the product from rain while it cures at the jobsite, since it arrives cured from the factory.
- Fewer workers required to assemble the house.
- No termite problems.
- The home's thermal mass keeps it cooler in summer, warmer in winter.
- It can be engineered to withstand high wind loads in hurricane-prone areas.
Changing perceptions
Coastal builders have traditionally been masonry-block builders to meet the hurricane wind loads, says John Blanchard, general manager of Manning Building Supplies in Lakeland, which is supplying the Quick Wall precast system for the Date Palm project. But builders in Central Florida are "stick builders" - they frame their homes in wood.
Or they did, until Hurricane Andrew did its worst in 1992, and until seven hurricanes in 2004 and 2005 blitzed through the state and inland builders began to seek a more hurricane-worthy form of construction.
In 1993, just 3 percent of all new American homes had above-ground walls made of concrete, and most of those were in Florida or Texas. By 2003 that figure had climbed to 12 percent, and the Portland Cement Association estimates that by 2010 it will be 25 percent.
Manning's factory opened seven years ago, and there are several other precast manufacturers in Central Florida.
Although it's less important in the current slow real estate market, the speed of construction is a selling factor Manning is counting on when the market rebounds. "We can put up a 2,500-square-foot house in half a day, as opposed to two weeks in block," he said.
Brian McElroy, president of McElroy Construction in Valrico, has been building precast homes exclusively for four years now. He just completed an 11,000-square-foot custom home in less than six months, a task that would take up to a year in block.
A 3,500-square-foot model he opened last weekend in Dover, packed with other energy-efficient features, has been certified "green." He expects the utility bills will be less than $100 a month.
Blanchard estimated that a precast home is 5 to 7 percent more expensive to build than a comparable block home. McElroy says there's no difference in price. "A lot of the builders we have put it as an option to the owner: I can have you in a precast house quicker," Blanchard said. Add to that lower utility bills and high wind resistance, and it's an appealing economic option for some buyers, he said.
Ready for weather
"It's not indestructible but close to it," said Mike Brinegar, vice president of the Cornerstone Group's townhome division that is building the City View townhome project in Tampa.
"Block is hollow. This is solid. It's not going anywhere. It's built like a concrete vault," he said. He also cited fire safety and energy-efficiency: "Even while it's under construction, it's cool inside with no air," he said. "You notice the difference right off the bat."
In case of storms, "it far exceeds any 120-mph wind code," he said. "The main thing is not necessarily the wind but what's in the wind that you're worried about. Windborne debris bounces right off."
Precast panels can be as wide as 30 feet and can weigh as much as 16,000 pounds. They come from the factory individually numbered so it's clear which one gets installed where. Once they're in place, finishing the home is very similar to working in masonry construction, Fernald said. Building inspectors are familiar with the construction system.
Precast works best on a site where cranes can easily get in and swing the panels off a flatbed. It's harder in a narrow, urban infill site with utility wires overhead.
It's also unforgiving of errors and poor measurement. Each panel is poured to exact specifications, with windows and doors and electrical boxes cut out. There's no wiggle room here if something is off - even by an inch. "The planning has to be pretty accurate," said Fernald, the contractor. "Things are where they are."
Brian Bock, vice president of Dukane Precast near Chicago, said precast will make its mark "by how quickly we build a quality product that's energy-efficient. We provide the whole gamut of solutions."
The new interest in precast doesn't spell doom for the block industry. "All concrete systems have been gaining in market share in recent years, mostly at the expense of wood-framing," Portland Cement's Niehoff said. "Masonry has more than held its own, particularly in areas such as South Florida. I think developers and builders will pick a given system based on whether or not they feel it offers the most viable economic solution to their particular construction challenge. Some of the variables involved will be availability of trained labor, proximity of manufacturing facilities and construction schedule. In other words, I think each system will have its niche."
Judy Stark can be reached at (727) 893-8446 or stark@sptimes.com.
Three precast projects
--The Villas at Date Palm is at 790 LaPlaza Ave. S in South Pasadena. There will be 30 townhomes in seven buildings: three bedrooms, 21/2 baths, two-car garage, elevator shaft/safe room, Simonton Storm Breaker windows. There are three floor plans, ranging from 2,075 to 2,590 air-conditioned square feet. Prices start at $395,000. Web site: www.thevillasatdatepalm.com. Information: (727) 341-2224.
--City View, a 138-unit townhome community, is at 4821 Bristol Bay Way, Tampa. There will be 17 one- and two-story buildings; units have two or three bedrooms. There are four floor plans, ranging from 1,140 to 1,438 air-conditioned square feet. Prices start in the $160,000s. Web site: www.cityviewtampa.com. Information: (813) 248-8500.
-- McElroy Construction of Valrico has just opened a 3,500-square-foot model precast home at 5008 Durant Road, Dover. It is open 10 a.m. to 6 p.m. Monday through Saturday, by appointment Sunday. Phone: (813) 657-2211. It is a certified "green" home with many energy-saving features and materials. The furnished, decorated model, on a one-acre homesite, is priced at $877,000. The company's Web site is www.mcelroycustomhomes.com.
FAST FACTS
Pouring it on
Mercedes Homes recently used poured-in-place cast concrete walls at two models at Grand Hampton, off Bruce B. Downs Boulevard in New Tampa.
A "birdcage" made of metal reinforcing bars is built around the perimeter of the slab where the home's exterior walls are to go. Then aluminum forms are placed on either side. Imagine a sandwich: The forms are the bread and the rebar is the filling. Concrete is pumped in, in one continuous pour, 6 inches thick, to create the home's walls. Once the concrete has cured and dried - likely within a day - the forms are removed.
Although this construction method costs about $3,000 more than a comparably sized block home, it has the same advantages as precast panels, customer service manager Matthew Longenecker said: high wind resistance, ability to withstand windborne debris and high energy efficiency.
Elsewhere on the web
-- View a video showing a precast home under construction at www.precast-homes.com (click on "watch a video").
-- See a precast wall resist a 2 by 4 fired by an air cannon at 105 mph (the equivalent of hurricane winds of 230+ mph) at www.fpcaweb.org.