Kansas City showcases concrete technology
By: Carole McMichael
Late in June, the NAHB's Concrete Home Building Council offers its Concrete Technologies Tour for builders in Kansas City, Mo. The three-day event will give builders a close-up look at a variety of cement-based building materials and systems, as well as the manufacturing plants themselves. They will be exposed to regional differences in trends and the role concrete plays in the residential market. From there, builders will be introduced to possible ways to include the latest concrete technology in their own construction methods.
The tour ends with a reception in the recently completed Worley house, home of Mr. and Mrs. Ross Worley, owner of Wall-Ties & Forms. Wall-Ties produces removable aluminum forms using cast-in-place concrete construction. The system offers forms with two-, three- and four-hole options; a variety of ties, blockouts and blockdowns; and hardware and accessories. There are also "brick-look" forms, super lightweight forms and bracing designed to simplify carrying and using the forms.
The concept behind the features of the Worley house was to create a model that would show builders the latest in removable forms technology in a finished project. The house used every piece of forming and apparatus Wall-Ties can make. In addition to the wall panels, for example, builder John Childs poured the steps, a round room, arched windows, a big radius-form swimming pool, a hot tub and a retaining wall. Not only does the house speak volumes for removable forms to tour attendees, it will continue to be a model for Wall-Ties' customers and for the builder as well.
"I have worked with the Wall-Ties system since 1999," said Childs, president of Secure Structures. "What I like about the process is the quality of the house when it is all done and the feeling you get inside the house. It is super energy-efficient, not drafty; the floors don't squeak, and you don't hear outside noises either. It feels more solid, the way a home should be built. I also like building with Wall-Ties because it's challenging, it's different. It is being on the cutting edge - hard, but fun."
As with most systems, the manufacturers keep fine-tuning the product to remain competitive. This is also true of Wall-Ties, according to Childs. There are many little changes, he noted, that make his work faster, such as the way he fastens boxes to the ceiling and deck panels, or the development of a more convenient ledger size. (The latter enables basement subs to use the forms doing walls and decks without having to buy a whole set of them.) In a nutshell, Wall-Ties redesigns pieces that make the system more accessible to the average poured wall contractor.
Basement or slab?
"Kansas City is the home of the poured wall, with three major manufacturers of poured wall systems," said Childs. "So it is not surprising that pretty much every house has a basement. They have been pouring basements here forever. Still, because the Wall-Ties system lends itself to slab on grade, the Worley house is a slab on grade. The system also lends itself to choosing a slab over a basement to make the cost halfway competitive with wood. Another advantage of slab on grade is that we don't have to have the scaffolding. That slows us down.
"When we do put in a basement, we insulate it, which is not done typically, and put in electrical outlets. Ours is three times the cost at the unfinished stage, but when we finish it, that is where the concrete house catches up. In our market, we have built two houses out of 20 that have been single slab on grade. The engineer said our slab could support up to five stories."
The Worley house
The style of the Worley house does not fit neatly into popular design categories, but at 6,200 square feet of living space, it presents an impressive facade of brick veneer in front and stucco on the remaining three sides. Some of the interior wall finishes are sheetrock with wood and some have plaster applied directly to the concrete. There are five bedrooms; the master suite and a guest bedroom are downstairs, and the other three, upstairs. There are five baths, a loft, a kitchen, a dining room, a living room and the family favorite, the theater room.
In this part of the country, tornadoes are an almost annual threat, making the concrete envelope provided by the removable forms system well-suited to including a saferoom. Probably the most common choice for doing double duty is a closet with a steel door. In the Worley house, however, the owner chose to make a very large saferoom out of the upstairs theater room. He added two steel doors and eliminated windows, which also keeps the room appropriately dark for showing films. The Worleys are probably the only people in the world who go upstairs in a tornado, noted Childs.
In line with the concept of showcasing concrete uses, Worley chose to use poured concrete for the three-car heated garage. Concrete builders often frame garages in wood because it is less costly and the energy-efficiency advantage of concrete is diminished by the garage doors. Clients with classic cars or other valuable vehicles opt for concrete because they are more interested in its protective and (as in this case) temperature-control properties.
Worley selected colored concrete for the driveway and stamped concrete to create a decorative decking area around the pool. The home contains both an aluminum spiral staircase and a concrete staircase. Because curved-wall features are fairly easy to achieve when using concrete framing systems (whether for rooms or landscaping), the design includes a variety of curves. Perhaps the most unusual was the semi-circle breakfast nook, which lined the curved wall with six arched windows.
Following the process
In the pre-planning phase, Childs sat down with the Worleys and determined the placement of outlets, lights and plumbing, room by room. Because the owners wanted the home to be a model for the system as well as a home, the project plans had to be flexible enough to respond to frequent new ideas and added rooms.
Said Childs, "Normally, I have an idea of what spans I can do and where to put a drop ceiling, so I put the concrete walls where I want. Next, I go to a structural engineer to do the calculations and put his stamp on the plans, and then have the draftsmen draw up prints for the city for permits, depending on the county.
"The 3-acre site for the Worley house was a sloped lot. We excavated out part of the hill and built a 4-foot retaining wall. That gave us a nice flat site. The soil was clay, but not the kind that will heave up because it doesn't hold much moisture. Anyway, the structural engineer's figures are always done for a worst-case scenario for soil.
"We load forms on a trailer with a skid loader. On site, the individual forms are carried and set by hand, one at a time. At the Worley house, we used a boom truck and lifted 40 forms at a time in a basket, then set the basket down for unloading.
"We poured footings, which are 24 inches wide and 16 inches deep on the exterior. Next, we formed up the slab and poured it. That makes it easier to set forms because working off concrete is easier than working on dirt or gravel. Then we shored up the form work with bracing off of that. Jack posts and screws were placed about every 6 feet, running the length of the wall.
"The corners were done with special corner forms that are different sizes on the inside and outside, so they line up. We used a transit to shoot elevation, but plumbed all the walls with a level and string line to make sure they were straight before we poured. We put wedges in the bottom if they were not straight or just kicked the wall to get it to the string line. Each time we poured, we shot the grade on the deck. Sometimes slab forms will be down a little bit, so we just shoot it on each elevation, so it will be nice and level when we finish."
Childs used a self-consolidating concrete mix when pouring the walls and a 4,000-psi mix on the ceilings. The mix includes pea gravel aggregate and a water reducer. With a self-consolidating mix, Childs needed only one man to go around checking, thus avoiding using separate crews to pour the walls and flatwork.
The Wall-Ties system uses a 5-pound-density, expanded polystyrene foam that is added on the outside of the walls. It comes in rigid 24-inch panels, which are cut to fit exactly so they retain tightness. Most of the forms can be removed the day after the pour. To prevent sticking on the forms, Childs uses a release agent, but noted that if used properly, builders shouldn't have to clean the forms.
"Depending on the size of a house, we put up the forms and do the pours in sections or all at once," Childs said. "Using all my forms, I can do a 2,500-square-foot footprint in one pour. For the Worleys' project, we did the house in three pours: the garage and kitchen area was one; the master, living room and other bedroom was one; and we did the second floor all at once. It took three weeks per lift with a six-man crew. When I do a time study, I keep track of all the time per man hour. On a Habitat for Humanity project, we formed up the house and poured it in a day and a half. The study showed that square footage per man hour came out the same as it does for most of our projects.
"My crew right now is just myself and one other guy, as we have slowed down for the winter. You can pour year-round, but we often don't. It is more about the mentality of the clients, who think they need to wait until spring.
"The Wall-Ties system is not hard to pick up, even for a green crew. Learning to assemble the forms - where the pins and wedges go in and the ties go - is pretty easy. The harder part is the rebar placement and window forming that you have to think about."
Childs trains his own crew. He prefers workers who don't know anything but are interested in learning, noting that the ones who just jump right in and try to do it seem to work out best. "I don't want workers who think they know it all because you can't teach them anything," Childs said. "The same is true with some subcontractors."
"There are several ways to do things, so I usually tell my crew, 'This is why we do it this way, but if you think of a better way, maybe we can try it.' I also do training for Wall-Ties. I like to work with them because they really want the system to work. They come up with new ways that make me faster. It's a two-way street."