Article No: 268

2009-12-22 10:26:16
Hambro, Speedfloor
By: Steve Samaha


The Hambro system features a joist design that keeps the wire mesh centered to the concrete pour without the use of stools.
 
A concrete home provides a resilient structure, immune from most natural disasters. The structural integrity, environmental benefit and thermal properties of most concrete homes exceed the standards for residential construction in the United States. However, one piece of the puzzle often overlooked is the floor and roof system.     

Building a concrete house with a wood floor or roof is rather like building a tank with a plastic turret. A new trend in residential construction is the use of joist-based concrete flooring systems that are ideal for residential construction projects. 

Two such floor systems that work well in single family or multi-family applications are the Speedfloor (speedfloorusa.com) and Hambro (hambro-floors.ws) concrete floor systems. Both systems are easy to install, cost effective for residential projects and they both provide the structural integrity necessary to withstand any disaster.    

Francois Dutil with Hambro states: “The original intent of the floor system was to replace the need for steel erectors. The concept provides a one-stop steel package for insulating concrete forms (ICF) construction.” 

These floor systems integrate well with ICF systems or masonry and allow the builder to provide a turn-key service.  Unlike traditional concrete flooring systems, both Hambro and Speedfloor can be installed by the same tradesman who builds the ICF walls. This fact eliminates the need for multiple subcontractors, thus speeding up the job schedule and significantly reducing cost.

Nick Ruebel with Speedfloor estimates that “an experienced five-man crew can install 10,000 to 14,000 square feet of flooring in less than a week.” 
The essence of both flooring systems is a steel joist that is placed on the wall by hand. The joists are light enough to be man handled, thus eliminating the need for cranes. Once the joists have been laid approximately 4-foot on center, a lock bar or roll bar is put in place. This keeps the joists properly spaced, supports the temporary plywood forms and provides lateral and torsional stability during the concrete pour. 

The next step is to lay 4-foot by 8-foot sheets of plywood on top of the joists, which will serve as the formwork for the concrete. Wire mesh is then placed on top of the plywood in 8-foot by 20-foot sheets to provide tensile strength to the concrete. 

Both Hambro and Speedfloor feature a joist design that keeps the wire mesh centered to the concrete pour without the use of stools. This feature further speeds the installation process. 

Finally, the concrete is poured, with a minimum thickness of 2 ½ inches of 3,000 psi concrete. Once the concrete sets within 48-72 hours, the lock bars can be removed and the plywood stripped from underneath the floor deck. Because no additional shoring is required, other trades can be working below the floor deck after the concrete has set, adding additional efficiency to the construction schedule.     

Steve MacMahan with Great American Rebuilders said:  “We can eliminate wait time to remove heavy timber shoring, which truly simplifies the construction schedule.

Additionally if my crew needs to make modifications in the field, we can trim the joist without having to consult an engineer.”

The joists themselves create an 8-inch to 16-inch chase for HVAC duct work and utility lines. A hat channel can then be attached perpendicular to the joists to provide a mounting surface for drywall, thus completing the system. With fire-rated drywall the systems can provide a one- to two-hour UL fire rating. Additional coatings can be applied to the joists to increase the fire rating as needed.

Concrete flooring systems for residential applications provide more than just structural integrity, they also offer safety and security. A growing design trend in the residential construction market is the offering of a safe core concept.

Many readers have probably heard of the safe room idea, in which one room is designed to provide additional protection for occupants in disaster-prone areas. However, the safe core concept is where the bedrooms are separated from the rest of the structure by providing more solid building materials such as concrete.

The safe core concept only works if concrete is provided on all six sides of the structure. That is only possible with a concrete flooring and roofing system. Builders who provide such systems can offer a competitive advantage by marketing their homes with the safe room or safe core features. 
For an ICF home, this process provides a sound structure ideal for hurricane- or tornado-prone regions. Both Hambro and Speedfloor have been tested to significantly reduce uplift loads commonly associated with high-wind events. The cast-in-place floor can be tied to the foundation and provides significant strength over traditional wood joist systems. 

What typically destroys a house during a hurricane is the loss of windows or doors due to wind blown debris. Once the shell of the structure is penetrated, the pressure differentials create tremendous uplift on the structure. The house essentially explodes, blowing out the roof and thus walls and floors. 

With a concrete floor or roof system, the ability of the structure to resist such uplift loads is significantly increased. Therefore, even if the shell were penetrated the house would remain intact. Both flooring systems are also ideal for seismic regions as the joists are free floating. Unlike a traditional concrete floor that acts as a continuous diaphragm, the joist system allows for greater movement and flexibility when a seismic event occurs, thus further reducing the possibility of total system failure.

These systems were originally developed for the apartment building, condominium or parking deck niche. However, approximately 70 percent of business growth is connected to the ICF industry. As with all new products, there is a learning curve. 

Speedfloor‘s Ruebel said: “Most contractors bid their first job a little higher in order to cover their bases. However, most of the contractors who use the product prefer it over traditional flooring systems once they understand it.”

Both companies offer a comprehensive training program for contractors and have project managers capable of assisting customers in the field. Great American Rebuilders’ MacMahan says that a new guy on the crew can learn the system in about two hours with onsite training.

For the designer, the benefits of using steel and concrete in the construction of green buildings include strength, lightness, recyclability and reusability. These flooring systems contain up to 72 percent recycled content within the steel joist. This is determined on a job-by-job basis and documentation can be provided for LEED certification. Concrete can be made with recycled fly-ash further improving the green footprint of the structure.

While concrete joist flooring systems are a few dollars more per square foot than wood systems, the concrete joist flooring systems do offer approximately 24 percent savings versus the traditional plank floor systems.

The added safety and security of a solid concrete structure is perfect for the contractor looking to provide a complete package to their concrete home project.

Steve Samaha is a freelance writer who owns Samaha Enterprises LLC of  Milton, Fla.