|Reinforced precast concrete wall panels used in Chicago scattered-site housing measure approximately 20 feet wide by 10 feet tall
As major cities re-examine their approaches to inner-city housing developments, precast concrete components are giving them another option. Designers are discovering that precast concrete wall panels can replicate city textures and architectural details while offering design flexibility, cost efficiency, quick erection and strong aesthetic appeal.
Where once municipalities focused on the efficient stacking of units into tall, multi-story complexes, today they are seeing advantages to creating scattered-site and infill housing that helps tenants fit into an established neighborhood. That trend has combined with innovations in producing precast panels and other components to create designs that meet the needs of housing authorities, developers, designers and the entire construction team.
|These two-story, infill housing structures built in Chicago, feature precast concrete wall panels on their façade that replicate brick and limestone. The design allows components to be used to create several styles of homes. Two key options include a gabled roof and a flat roof (that actually is slightly pitched to the side to allow for rain and leaf runoff
An example of the possibilities can be seen in a series of projects currently underway in Chicago. There, several one- and two-family homes already have been finished and another project featuring similarly styled row houses is underway. Ironically, the program's catalyst came not from local officials looking for alternatives, but from the precaster's desire to find cost-effective uses for existing forms and the realization that many current infill housing designs did not adapt to their neighborhood surroundings.
"We had lots of form capacity that we'd been using in a vertical configuration to create soundwalls in along Chicago's expressways," explains Chris Newkirk, president of Prestress Engineering Corp. in Prarie Grove, Ill. "I was looking for other options for using the forms when it struck me that a lot of the infill housing produced in the city tends to have a suburban style to it, which looks out of place. I realized that those soundwall components, turned sideways, were just about the right dimensions for a one-story wall of a home - and the textures we could create would fit the neighborhood's look much better." Seeing opportunities, company officials began talking with local companies about the potential.
After three years of contacting various developers and contractors and constructing a prototype at his plant, Newkirk created a partnership with Affordable Construction Concepts LLC, a developer and contractor that brought in its architectural firm, Piekarz Associates P.C. The three firms worked together to design houses for the Chicago market.
First In The Nation
"Precast concrete hasn't been used as an option on any significant scale in the residential housing market," explains Bill Von Der Ahe, president of Affordable. "Not only are these projects the first we've ever done, but we believe they are the first time the industry has ever been involved with projects in this way. Nothing ever has been sustained on any basis using this style, especially with this quality, and we intend to change that."
The homes feature three floors of living space with 800 square feet per floor or 2,400 square feet apiece. The buildings measure 21 feet wide and 42 feet long and are composed of 18 reinforced precast concrete wall panels. Each panel measures approximately 20 feet wide and 10 feet tall.
The project's greatest challenge came in creating a housing concept that met the requirements and worked within the confines that the team set for it. Specifically, they wanted to use the existing soundwall forms to minimize costs. They wanted to create a design that fit virtually any urban setting yet was modular enough to be replicated many times without needing new drawings to adapt to a specific location or target audience.
"The key ingredient was designing a home that made maximum use of the existing precast forms," explains Ron Piekarz, principal in the architectural firm. Designers created new form liners for the 15- to 16-foot forms using molds from actual masonry designs to replicate the style they sought. They also decided to design the liners sideways from the original tall forms, says Newkirk. "We didn't want to have to rotate the panels once they were cast," he explains. "That's the point where the most stress is produced and damage might occur."
One significant benefit came from the panels' 4-hour fire rating, which is higher than that achieved by other materials. Not only did this provide a safety advantage that could be promoted to owners and tenants, but it also provided design flexibility in the relationship of the building to the lot line.
"The higher fire rating allowed us to build right up to the lot line," Piekarz says. "That let us build the widest possible homes on the lots and added roughly 20 percent to the width of the house." The added width allowed bedrooms to be laid out side-by-side instead of the traditional format of front-to-back on the narrow Chicago lots. "This significant change creates a more-pleasing interior layout, which tenants find more comfortable and owners find easier to rent," Piekarz notes. "It's amazing what a couple of added feet to the width can do to reconfigure the interior."
The use of precast panels also allowed designers to eliminate foundation walls around the basement, saving more cost. "We set the panels directly onto the footings, which eliminated the need for formwork and the time required to pour traditional walls," Von Der Ahe says. In addition, this format allowed the precast panel to provide a monolithic face at grade level, reducing the possibilities for water infiltration at this key point since there is no joint through which moisture can penetrate or degrade materials. The project's greatest challenge came in creating a housing concept that met the requirements and worked within the confines that the team set for it. Specifically, they wanted to use the existing soundwall forms to minimize costs. They wanted to create a design that fit virtually any urban setting yet was modular enough to be replicated many times without needing new drawings to adapt to a specific location or target audience.
Another cost-saving advantage came in the speed with which the home's shell can be constructed. "Because the precast panels are cast under factory conditions away from the site, quality control is higher, tolerances are much tighter and little room is required at the site to prepare the panels for erection," explains Newkirk. "And since the panels are cast in a controlled, heated environment, they can be produced year-round and erected even in harsh winter weather. That extends the typical Chicago home-construction season from about nine months to a full 12 months."
The result can be quicker return on investment and a lower long-term cost of money, Von Der Ahe points out, because revenues are generated to pay loans quicker. The quick construction also aids on-site security, notes Piekarz, since no construction materials need to be stacked and left unsupervised overnight while the shell is being erected.
In each case, the entire precast envelope was erected in one eight-hour day. Then interior trusses were laid, decking was applied, and windows and doors were installed. This produces a tight shell that gives other trades quick access so they can begin interior work faster. To achieve this one-day erection sequence required considerable rethinking of connection procedures and designs.
"Even though the panels aren't as large as typical architectural precast concrete panels, they require the same connections to secure the concrete," Newkirk explains. However, Prestress's engineers determined that to provide typical welded connections would take nearly 24 hours of welding to finish one job. This was deemed unacceptable to cost constraints, so a bolted-connection design was substituted. "The new design worked extremely well and reduced connection time to 8 hours per house," Newkirk reports.
Design Mimics Brick
With cost efficiencies determined, designers turned their attention to creating a design that fit into existing neighborhoods. This was achieved by creating form liners that mimicked the look of brick and combining them with precast accent bands cast to resemble limestone coursing. The accents run along the house's base at the half-level above grade, between the two floors of the home and along the roofline.
A key challenge came in producing the grout lines that make the brick appear realistic and provide a three-dimensional look to the facing. High quality-control was required to ensure these elements retain their consistency and realism. "We were very impressed with the work," Von Der Ahe says. "The finished panels feature absolutely straight grout lines - which even a mason using true brick would have a hard time replicating."
Another challenge centered on producing the grout lines and brick returns around the doors and windows, to ensure the side views on these elements maintained the illusion of real masonry. The windows in the home are set back from the edge, providing shadow lines and architectural features, and the returns needed to make this visually consistent were achieved with some experimentation prior to achieving the final design.
The combination of textures produced a traditional-looking design that fits into a wide range of urban neighborhoods regardless of income level. In addition, the design was created so the home can include a gabled roof, featuring a limestone-like front facing, or a flat roof that actually is pitched slightly to one side to allow for rain and leaf run off. "This eliminates the need to maintain the rooftop, while ensuring the home will fit into a neighborhood where flat-roof structures predominate," explains Von Der Ahe.
Key Housing Advantages
Using precast components produced several additional advantages for housing construction that appealed to municipal housing officials. Maintenance is considerably lower for these types of walls than for a vinyl-sided home. Precast wall panels also are much more resistant to wind, water and insect damage, and they're considerably more durable than a vinyl siding/gypsum wallboard combination, adding structural stability, acoustic control and protection from damage and abuse.
The team agrees that the use of precast concrete components can be pushed further to reduce costs once building officials and potential tenants become comfortable with the concept of replacing existing building materials with more-efficient ones. "Ideally, we could design these homes using insulated precast concrete wall panels," explains Von Der Ahe. "That way would achieve both a high energy-efficient wall, as well as provide both interior and exterior finished surfaces. That would speed construction, while providing an aesthetically pleasing finish to both the neighborhood and tenants."
For their initial foray into the field, the team decided to use more-standard wood-furring and wallboard interior walls to better replicate the environment with which tenants were most comfortable. In addition, the design team wanted to use as many local contractors as possible to finish the housing, and keeping to standard construction methods ensured there were no special requirements needed in hiring subcontractors to finish the homes.
For those same reasons, a traditional open-web, wood-truss floor structure was used rather than hollowcore plank. "hollowcore would have given us advantages in acoustic control, fire rating, speed of erection and durability," Piekarz acknowledges. "But we decided to play it safe and produce a home that did not give any indication of being built of concrete." Ensuring that tenants shoes echoed on wooden floors provided that reassurance for this early stage of developing the concept. "As the program develops, hollowcore plank would be a strong option for reducing costs and speeding construction."
Adds Newkirk, "We're bringing a new product to market, one that's unfamiliar to designers. We wanted to take it one step at a time, gain acceptance and then refine it." These precast components will be particularly helpful if the designers can achieve their goal of producing a "kit of parts" format. Then, a variety of home options can be produced from a small group of components, allowing them to be stocked and ready to go when construction is approved.
To secure the wooden floors, special anchors were bolted to the inside faces of the wall panels during their casting stages. This provided a ledge to attach the open-web wood trusses, which allow mechanical elements to run through them. A pole-bracing system was designed so as each story of the precast panels was erected, the trusses could be placed inside in a bundle. Once the first-floor panels were in place, the bundle could be opened, trusses laid across and flooring deck applied quickly. The trusses were marked to allow for special conditions, such as stair openings, to ensure each laid in quickly but accurately.
Key Restrictions Apply
The team warns that some restrictions do apply when considering this type of residential construction. "You have to be somewhat site-selective, as you need room to maneuver a crane," explains Von Der Ahe. In Chicago, elevated train tracks and narrow streets need to be plotted to ensure logistics are acceptable. The masonry-like design and long, narrower style lends itself more easily to urban settings than suburban ones, where styles are more diverse and land is more sprawling.
The homes already built have generated considerable attention, the team reports. That includes recognition from the design community. Last year, the project won a PCI Design Award for Best Hotel/Housing. Even more important, City of Chicago officials have been impressed. "The design more than satisfies community leaders and the consumers, both in the look and costs," Newkirk reports. "They really like the product and the communities it produces. It's a much nicer look and a far better product than they could achieve with stick construction and vinyl siding."
Motel Features Precast Façade
The same soundwall-type wall being used on residential designs in Chicago also has been adapted for a recently constructed motel. The Amber Inn, a two-story, 90-room hotel with banquet facilities, was completed in July, just seven months after the project began in December 1997.
The design reflects the same style used for the residences, reports Chris Newkirk of Prestress Engineering Corp., except designers used hollowcore plank instead of wooden trusses for the floors and roofs. The panels consist of 35,000 square feet of precast concrete cast with a brick texture and design. As with the residential units, accent pieces were provided for sills and copings.
"This design gave us considerably faster speed of construction, especially since we were building through the winter months early on," says Ron Piekarz of Piekarz Associates P.C. "The precast concrete helps to expedite the construction schedule, allowing us to cast the walls while excavation was continuing. The fire rating also was a key benefit for the owners. And the accent pieces provided a very rich look for the aesthetic design."
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