The stats remain fairly stable: 93% of new homes in the U.S. are wood-framed; concrete homes make up about 7%, and steel-framed homes less than half a percent of the market share, according to NAHB analysis of Census Bureau data tracked over the past five years.
In spite of the challenges that wood framing has faced—declining quality of the lumber, tariffs on lumber, the threat of moisture in the wall system, potential for termite infestation, VOC emission liabilities— many builders and their subs are knowledgeable and comfortable with wood-stud construction; this makes them less likely to use other building methods. However, what used to be considered “advanced framing” techniques have been adapted into the mainstream due to increasingly stringent energy and structural building code requirements.
“Advanced” Framing for Walls Becoming the Norm
Wall frames provide the most opportunities for material savings when advanced framing techniques are used in place of conventional framing methods. Advanced framing uses fewer framing materials, yet boosts structural strength and energy efficiency, lessens environmental impact, and lowers labor costs.
It’s now widely accepted to build walls with 2×6 wood studs spaced 24 inches on center. Sheathing them with OSB or plywood allows compression and tension loads to be directly transferred to the vertical framing members under the roof trusses or rafters. Wood structural panels furthermore allow for greater architectural flexibility in the number and location of door and window openings, and the fact that the sheathing serves as a base for fastener attachment between the studs supports the cost-effective use of virtually any type of siding product.
Single, rather than traditional double top plates and headers, insulated two- or three-stud corner junctions, minimal use of jack studs and cripples, elimination of redundant studs and unnecessary blocking and bridging, and ladder junctions at interior wall intersections are other advanced framing techniques. All of these advanced framing techniques reduce the potential for insulation voids and create more space for cavity insulation.
Floor Framing: More Than Just Initial Material Costs to Consider
For floor systems, the Engineered Wood Association recommends wood floor joists (such as I-joists), structural composite lumber (SCL) and/or glulam at 24 inches on center and encourages engineers to maximize member spans between supports. Specifying I-joist floor systems between finished floors will typically allow for the installation of plumbing, electrical and mechanical services within the floor frame cavity, eliminating the need for dropped ceilings.
Thicker floor panels are recommended for a stiffer, more solid floor structure. OSB (oriented strand board) or plywood subfloors are typically a 3/4-inch tongue and groove panel, nailed or preferably screwed down. The glues and processes used to make both OSB and plywood, however, make the panels prone to soaking up moisture when it rains on the wood structure before it’s died in. Up-and-down floor movement is caused when edges swell, leaving gaps beneath the floor underlayment, leading to a creaky floor and a callback. Plywood and OSB manufacturers try to improve this by sealing the panel edges, but the sealant, whether it is a wax or a paint, tends to get scuffed off. Higher-density, more water-resistant OSB products, like AdvanTech panels are made to specifically address this problem. AdvanTech panels use an advanced liquid coating during the manufacturing process to make sure the panel is thoroughly protected.
Prefabricated insulated structural components that simplify construction such as insulated headers and insulated corners, are becoming commonly available. The Tstud™ is a newly engineered building product that uses two lumber members, an internal truss system, and a frothed-in-place closed-cell foam.