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August 1, 2002
Americans have been building homes with wood—shaping logs, joining timbers, nailing studs—for almost 400 years. Our current approach, stick framing, grew popular in the mid-1800’s (particularly in the rapidly growing “West”) because it took less skill, required simpler tools, and took fewer people than timber framing. We apparently really like waste haulers, too. The NAHB Research Center reports that the “typical” home generates about 3,500 pounds of wood waste during its construction, about half of which is solid sawn lumber. There are opportunities to use wood more efficiently at every stage of a home’s design and construction to save time, money, energy, and resources - you could call this optimum value engineering (OVE) from start to finish.
Setting the Stage
Americans have been building homes with wood—shaping logs, joining timbers, nailing studs—for almost 400 years. Our current approach—stick-framing—grew popular in the mid-1800's (particularly in the rapidly growing “West”) because it took less skill, required simpler tools, and took fewer people than timber framing.
We still like building homes with wood. According to the NAHB Research Center’s Annual Builder Practices Survey - 1999, 87.7% of the 1.7 million homes built that year, single-family and multi-family, were stick-framed.
We also like building with lots of wood. The National Association of Home Builders (NAHB) reports that a “typical” home takes just over 13, 100 board feet of lumber. That’s about three-quarters of an acre of forest just for framing lumber.
We apparently really like waste haulers, too. The NAHB Research Center reports that the “typical” home generates about 3,500 pounds of wood waste during its construction, about half of which is solid sawn lumber.
So, let’s do the math for US home building each year (assuming that 1999 is a representative year, which it was, just slightly above the average over the last 5 years):
- just under 1.5 million homes stick-framed,
- consuming just under 2 billion board feet of framing lumber, and,
- generating just under 1.3 million tons of solid-sawn wood waste (throw in another million plus tons of engineered wood waste—mostly plywood and OSB—for good measure).
Laying out the opportunities
There are opportunities to use wood more efficiently at every stage of a home’s design and construction—you could call this optimum value engineering (OVE) from start to finish. Most people think of OVE as a method of wood frame construction, limiting the concept to just a part of the total building process. But OVE is getting the most bang for your buck throughout the building process.
Lots of builders just don’t like the term OVE, regardless of how it is used. It implies changes or solutions offered to builders but not by builders. Throughout this paper, every wood efficiency concept is supported by Building Science Corporation’s field experiences under the Department of Energy’s Building America program. Building America is all about taking ideas from the office to the field with our nation’s leading production builders. That’s from builders, for builders, period. Many aspects of efficient use of wood are inter-related, complicating or even confounding categorization. We find it useful to layout the opportunities in the following way:
- design and layout
- material selections and purchase
- delivery and on-site storage
- framing techniques (including an innovative new shear panel)
- waste/disposal (including an innovation called the SEE stud)
We say opportunities because, more often than not, using wood more efficiently saves time, money, energy, and resources—for you, your customer, and your community. Given its goals, this is why wood efficiency has been such a good fit for the Building America program. (See case studies on pages 18 — 26.)
Design and Layout
There certainly is a lot more to consider in home design than framing efficiency; there are aesthetics, marketability, utility, and siting, just to mention a few. But framing efficiency does not have to come at the expense of the others. A reasonable balance can result in efficient and beautiful buildings. Efficiency does not mean forcing it into every nook and cranny of your design; it means employing any or all of the techniques below when it makes sense and cents.
We have grouped design and layout together because we feel there is a natural and inextricable relationship between the two. The design informs layout, but we think that the reverse should be true as well. It represents
the good fit that can exist between architecture and engineering in residential buildings.
Every jog added to a square or rectangular building footprint can challenge framing efficiency, some more than others. The trick is to include framing material and framing layout considerations during building design. It is possible to engineer an elegant home, but only if the full range of structural materials and their properties are an intentional part of the design process, not an afterthought.
Real estate developers often play a game of inches when it comes to room dimensions, but it is easy to satisfy buyer expectations regarding room sizes and still use modular design. Modular design is basically using two-foot increments as often as possible, taking full advantage of the material dimensions supplied by the manufacturing industry, particularly sheathing goods and large framing members. In general, it makes more sense to optimize for outside dimensions and hence framing/ wood sheathing materials than it does to optimize for interior dimensions.
- Integration of design with framing and the HVAC system
The performance, complexity and even the expense of the HVAC system can be driven by its relationship to framing layout and design, particularly with respect to duct layout. Some forethought about wall locations, direction of floor framing, and depth and type of floor framing members can result in some beautiful synergy between the framing and HVAC systems. Its absence can bring framing and thermodynamic chaos, and all for no particularly good reason. See Figure 5 for an example.
- Detailed framing plans
It pays to do detailed framing plans, both as a double-check on opportunities for efficiency gains from small design modifications back at the office, and as detailed guidance for the framers at the job site. We have found that detailed framing plans must make it to the job site, particularly when elements of efficient framing are new to the crew or crews. And, there is nothing worse than a mandate coming from the home office about efficient use of wood accompanied by designs and layouts that make efficient framing difficult, cryptic or even impossible. Detailed framing plans can make the difference. (Detailed framing plans don’t hurt with local building officials either, giving them advance notice and heading off subsequent approval issues.)
Material Selections and Purchase
Some materials inherently make better use of wood resources than others; some materials come from inherently more resource-efficient sources. This provides two more opportunities to optimize your use of wood resources.
- Engineered wood products (EWPs)
Any wood product that derives at least some of its structural properties from more than just natural wood fiber or solid-sawn lumber is an engineered wood product. They all contain adhesive or mechanical fasteners, or both. EWPs tend to be more consistent in their performance properties than their solid-sawn counterparts; less tolerant of site modifications; and more flexible in extending design beyond what is possible with solid-sawn counterparts. In recent years, many EWPs have become very competitive in price with solid-sawn counterparts.
Because EWPs (except plywood) utilize smaller, fastergrowing trees, they can relieve pressure placed on more environmentally sensitive old-growth resources. (With the exception of some pressure-laminated thin fiberboard sheathings such as ThermoPly“, no structural EWPs currently being produced utilize any recycled wood.) EWPs range from oriented strand board (OSB) to floor and roof trusses, to horizontal framing members such as I-joists, laminated veneer lumber (lvls), and glulam beams. Their use can increase spacing schedules, yield deeper framing cavities for accommodating mechanicals, and result in fewer problems with the cross-width shrinkage common in deeper solid-sawn framing members. Although it is always possible to use any wood resource inefficiently (including EWPs), EWPs generally represent the opportunity for more efficient wood use.
- Wood products from sustainably harvested sources
As a renewable resource, wood has inherent resource efficiency. But there is quite a range of harvesting practices, within and beyond the United States. True renewability necessitates harvesting practices, replanting, and forest diversity maintenance that sustain the resource. There are currently four forest certification programs active within North America—the American Tree Farm System, the Canadian Standard Association’s (CSA) Sustainable Forest Management Program, the Forest Stewardship Council (FSC) program (http://www.fscoax.org), and the American Forest and Paper Association’s (AF&PA) Sustainable Forestry Initiative. Only one program—the FSC-certified program—requires third-party certification, chain of custody documentation, and product labeling; attributes that we think are crucial for long-term efficient wood use. But judge for yourself—all of the programs represent significant departures from long-standing unsustainable harvesting practices and can be compared: http://www.certifiedwood.org/index.htm. This site also includes a nationwide sourcing database for FSC-certified wood products. The availability of FSC-certified solid-sawn wood products is still limited but definitely growing; on the EcoVillage Cleveland Building America project, we had no trouble specifying FSC-certified lumber in terms of availability or impact on the budget.
Delivery and On-Site Storage
It's pretty easy to just lay this out in simple terms—only deliver to the job site exactly what you need and then treat the materials with respect once they arrive.
- Waste factors
You always need to pad the lumber take-off with a "waste" factor, to account for bad stock and labor errors on the job site. But the question is: what waste factor is reasonable—is it 5% or 15% of the take-off? One job site proverb applies here: you send it, we will use it. Only you know just how closely you can set this factor, but detailed framing plans can work well with a honed-down waste factor. And some builders are experimenting with color-coding or some other way of designating stock so that there is an easy way for everyone from the site super to the carpenter's helper to know for what use each stick was intended.
- Dunnage and Coverage
It's pretty amazing to see how disrespectfully lumber packages can be treated on the job site—lifts sitting in mud or puddles of water with no top cover. Why pay for kiln-dried stock and then treat it like landscaping material once it gets to the job site? The performance of wood products — particularly sheet goods — can suffer if left exposed. Protecting wood products on the job site prior to their use is cheap and simple—stick the load to keep it up off the ground and top cover. It will remind your framing crew that they work with valuable product and show your potential homebuyers how you manage what could soon be their materials.
Download complete report here.