Conventional framing techniques use about 15 percent to 20 percent more framing material than is structurally needed, according to the U.S. Green Building Council (USGBC). Those extra materials represent wasted dollars.
The challenge for any particular multi-housing building design is, which joists, beams and other framing members can be left out while maintaining a safe, code-compliant structure? For wood-framed buildings, several technologies can help optimize material use and reduce costs. These include software for designing and evaluating structural floor systems before construction begins, and specifying pre-cut and labeled framing packages.
The goal isn’t to build the cheapest floor, but to better match the floor’s performance to the specific needs of each building project. Whereas a low-cost floor designed to building code minimums may be sufficient for affordable apartments, occupants of high-end condos typically expect a firmer floor. Design tools can help work out cost-effective solutions for various classes of projects and avoid excess materials.
Improved floor system design
Structural frame design software enables building development teams to obtain detailed floor framing plans that show the precise size and location of every framing member. Designers can use such tools to evaluate a range of factors that affect floor performance and cost. These include joist size, spacing and span, as well as floor panel thickness. The software then provides a detailed material list, which can help avoid unnecessary costs from over-ordering.
Some framing design programs also incorporate performance ratings that help predict how the building occupants will perceive the floor’s quality. They can evaluate structural materials to provide a sense for how the completed floor will feel. Such ratings can also take into account how other framing components, such as wall placement, affect floor performance. In multifamily structures, this can be particularly helpful since the larger number of interior walls can help dampen floor vibration, thereby allowing for more efficient framing.
Software with a floor rating prediction system built-in enables designers to readily evaluate various floor framing configurations and materials to balance performance and cost. The project developer can then make an informed decision whether a given level of performance is worth the cost for a project overall, or even within certain rooms. For example, a high rating may be especially important in rooms with a lot of traffic such as living rooms, kitchens and common areas, but less important in bedrooms or home offices.
Some structural frame design software packages can also go beyond floors to design and optimize all members in the roof and walls. Designers can view the structure from all angles and identify and solve framing conflicts on screen. This helps reduce the potential for costly framing fixes on the job site and provides a way to design a solid structure with just the right amount of materials. As a result, this software can help reduce material cost and construction site disposal fees.
Project teams can further expand the benefits of designing a cost-effective floor by using framing materials pre-cut and labeled at a lumberyard, rather than on the job site. This can help reduce building cycle time and virtually eliminate scrap created during floor framing.
Lumber and building material dealers typically stock large quantities of framing materials in various sizes, allowing them to plan cuts better than is possible in the field. For example, if a floor design calls for multiple 22-foot I-joists, they can cut the appropriate lengths efficiently from a range of inventory, including from pieces remaining from other jobs.
Using computer-controlled saws, dealers can make precision cuts within 1/16 inch, label each piece according to a detailed framing plan, and bundle and deliver the materials ready to install. Project teams can order a range of specialized framing members suited to each building’s need, including angled cuts, bevels and pre-drilled holes for pipes, wires and conduit. These various factors can help reduce the need for skilled labor on site, and lessen the risk of framing errors arising from language barriers among crewmembers and foremen.
By comparison, contractors doing all the work on-site would likely cut needed 22-foot lengths from standard-size joists (such as 24 feet), creating several feet of scrap per cut. Or, a crewmember may inadvertently cut a 22-foot piece from a long-length joist required elsewhere (say 30 feet), resulting in the need to re-order the long joist. This can add to material and delivery costs and potentially extend the construction schedule.
Because multi-housing buildings often contain hundreds of I-joists and other framing members, using pre-cut and labeled material kits can substantially reduce wasted materials, scrap disposal costs and jobsite labor needed to make cuts.
As developers, designers and contractors are under increasing pressure to cut costs, additional planning of the structural frame can be one way to help drive out unnecessary expenditures. This is true for affordable, as well as high-end, multi-housing projects. Design software and pre-cut framing can be used for virtually any low-rise building to help teams complete quality projects under tight budgets.
Tim Debelius is an engineered wood product manager for iLevel by Weyerhaeuser, which offers a range of residential, multifamily and light commercial construction framing materials, technical support and software.