Fortacrete Structural Panel wins on the Courthouse Square residences

The Courthouse Square complex is a cornerstone development in the renaissance of downtown Wheaton, Ill. The $93 million project includes a former courthouse converted into high-end residences, 50 luxury town homes, and three new condominium buildings.

Focus Development, Inc., the developer of the new condominium buildings, faced a number of challenges to meet the project goals. Among them was the need for significant green space surrounding the buildings and the inevitability of a winter construction schedule. In solving one challenge, another often arose.

These challenges pointed to the solution of a framing and flooring system that was lightweight, non-combustible, quick and easy to install, and resistant to the elements during bad weather construction. The design team chose a steel post-and-beam interior with cold-formed c-joists and a flooring system composed of Fortacrete Structural Panel—a non-combustible cementitious panel that can carry gravity loads and diaphragm loads when attached to steel framing.

Fortacrete is a 3/4-inch, 4-foot by 8-foot cement panel with tongue-and-groove edges. Developed by engineers and scientists at the USG Research and Technology Innovation Center, it is sturdy, repellent to pests, and impervious to rot and mold. When used as the floor sheathing in a cold-formed steel framed structure, it can significantly reduce the dead weight of the structure.
Low- and mid-rise multifamily and light commercial buildings, in particular, benefit from the Fortacrete system because it combines the durability of concrete and the non-combustibility of steel with a carpentry-trade-based installation method. Workers can cut panels using a carbide-tipped saw blade and a circular saw equipped with dust collection or suppression. Fastening is also conventional, using a screw gun and self-drilling screws.

On this type of project, the Fortacrete floor system provides an alternative approach that is often faster, stronger, safer, and less expensive than traditional methods.

This brings us back to the challenges that Fortacrete helped the project team overcome as they constructed the first of the three condominium buildings at Courthouse Square. Completed in 2007, the building houses 50 condominium units of 800 to 2,000 square feet.

The need for green space

Being a place where people live and work, Courthouse Square required green space to make it more attractive to potential residents and more aesthetically agreeable to city officials reviewing the project. However, with hundreds of residential units among the three new condominium buildings, the townhouses and courthouse building, and parking needed for residents and workers—all on a little over six acres in downtown Wheaton—there wasn’t an abundance of room for trees, grass, and gardens.

To help achieve the green space goals, the design team incorporated a precast concrete parking garage as a building podium for each of the three new condominium structures. The decision to integrate the parking into the building footprint allowed 55 percent of the surrounding area to remain green.
The garage podium concept was a preferable alternative to the excessive cost of excavation and fill removal that would have accompanied placing the parking structure entirely underground. A key to making this approach work was ensuring that the weight of the structure above was not prohibitive.
"The design dictated that we needed a lighter-weight assembly above [the garage] to mitigate the weight on the foundation below," said Pat Ford, P.E., principal of Matsen Ford Design and the structural engineer of record on the building. "That’s one factor that drove the decision to use Fortacrete. We needed a light framing assembly, and cold-formed steel combined with Fortacrete gave us that."

A mixture of lightweight Portland Cement, ceramic micro-spheres as aggregate (rather than sand), and alkali-resistant glass reinforcing, Fortacrete Structural Panel weighs less than 5 pounds per square foot. This clinched the decision when compared with the 30 to 50 pounds per-square-foot of dead load from poured concrete or precast panels.

Two-hour fire-rated floor assembly and finished floor appearance

The height of the structure atop the garage podium required Type II rated construction, including a two-hour fire rating for the floor assemblies. The decision to use cold-formed steel with Fortacrete fit this need as well.
Fortacrete panels meet the design criteria specification ASTM E136, for use in all types of noncombustible construction. In addition, it has UL listed two-hour fire ratings in several system combinations and with all types of floor coverings (including carpet and pad, ceramic tile, and engineered wood). On Courthouse Square, the design team chose single-layer drywall with a 1-1/4-inch-thick gypsum leveling topping over the Fortacrete to achieve the desired fire rating.

Also, to optimize the number of units they could fit in the allotted space, Focus Development required unit size flexibility and open, clear-span areas. With nine different condominium design templates of between 784 and 1,900 square feet—in addition to nine penthouse units of 1,660 to 2,100 square feet—a cookie-cutter design wasn’t going to work.

"The architectural design of the building had nooks and crannies, recessed balconies, and setbacks," said Ford. "It required a lot of flexibility, which led us to the unique solution of a steel post and beam interior with cold-formed c-joists of various lengths. To do that, and to eliminate the trade conflicts we would have had with deck and lightweight concrete, we chose Fortacrete for the floor sheathing. The system came in handy because it met the fire ratings, it married well with the joist assembly we felt we needed to adapt to the architecture they wanted, and it is light weight."

Fast, flexible, weatherproof schedule

As with most residential and commercial projects, the sooner the project is completed, the sooner the developers can begin to recoup their investment.
So fast completion and flexible scheduling—including completing much of the construction during the inhospitable Midwestern winter—was paramount.

By choosing a cold-formed steel frame structure with the Fortacrete flooring system, the project team ensured that the contractor could build through the winter. Unlike plywood, Fortacrete panels resist the effects of freezing/thawing, swelling, mold, and rot. The panels were stored onsite with no special requirements to protect them from the elements.

With the Fortacrete system, the framers who erected the steel frame also installed the floor. This meant fewer trades onsite, less specialized equipment being shuffled in and out, and no complex schedule to accommodate multiple tradesmen working on the job.

"The biggest thing is that my framing contractor didn’t need to leave the site to allow the metal decking contractor and concrete contractor to complete their work," said Randy Norbeck of Focus Development. "The metal framing contractor can stay onsite and we can continue the process. We save time on the schedule and one contractor performs the work. So it’s much easier to manage, both from a field standpoint and from a paperwork standpoint."

The framing contractor, RG Construction from Elmhurst, Ill., had no down time waiting for other trades and was not delayed by weather. They also used the installed Fortacrete flooring to hold temporary bracing and jigs, which further accelerated the pace of construction.

"What I like about it is that we’re not held up as a carpentry outfit," said Jack Pfeiffer of RG Construction. "We come in, put this product down and, when we finish, we can start building our walls and standing them. In the past, when we’ve done plywood and we’ve done pan decking, there’s a delay between being on one deck and getting on the next deck after it’s been poured. We can be down a week maybe a week and half, depending on the weather."

On the first condominium building at Courthouse Square, completion of each level—including laying the Fortacrete, setting the exterior walls, and hanging the joists for the next floor—was 13 days on average for a 12,000-square-foot floor plate. In all, it took fewer than 80 days from completion of the podium to when the framer completed the seventh floor deck.

"This product also acts as diaphragm for the building," added Pfeiffer, who used Fortacrete for the first time on the Courthouse Square project. "It’s strong enough to take the stresses that typically would be picked up with pan decking and the concrete. That’s a big plus from the get-go."

Kumar Natesaiyer, Ph.D., is a civil and structural engineer and the manager of sales and market development for the Structural Technologies Group of Chicago-based USG. He was co-inventor and on the team that developed Fortacrete Structural Panel, and can be reached at fortacrete@usg.com.