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| Sustainable Building Sourcebook | ||||||||
| Chapter: Materials | ||||||||
| Optimum Value Engineering | ||||||||
| CSI Numbers: 06100 Rough Carpentry | ||||||||
| Introduction: | ||||||||
| Optimum Value Engineering (OVE) refers to design and framing techniques for wood construction that were developed by the Forest Products Laboratory and the National Association of Home Builders approximately two decades ago. Buildings designed and constructed employing proper OVE practices use less lumber while maintaining their structural integrity, which lowers costs for both the builder and the owner. The builder saves money by reducing the amount of lumber purchased, transported, cut, and hauled away from the jobsite. The resulting building has improved thermal performance, as insulation replaces wood members; this results in energy savings for the owner. OVE techniques can be implemented in both the design and the construction phases of the project, and include: designing the building on 2-foot modules; aligning openings with stud spacing, increasing wall stud spacing from 16" centers to 24" centers; spacing floor joists, roof rafters, and/or trusses at 19.2" or 24" instead of 16"; utilizing single top plates at walls and aligning floor, wall, and roof framing members such that loads are transferred directly; sizing door and window headers correctly and eliminating headers in non-load-bearing conditions; using 2 instead of 3 studs at corners; and ladder blocking where interior partitions meet exterior walls. These and other techniques are discussed in the "Guidelines" section of this chapter | ||||||||
| At-A-Glance Notes: | ||||||||
| Technology: | ||||||||
| Traditional framing crews using standard tools, fasteners, and materials can implement OVE practices; however, some training may be necessary, as some crews may be unfamiliar with OVE techniques. | ||||||||
| Suppliers: | ||||||||
| OVE materials are readily and widely available; choosing suppliers who can provide pre-fabricated joists and trusses and custom-cut studs reduces on-site labor. | ||||||||
| Cost: | ||||||||
| Up-front costs for OVE practices are higher than in typical projects; however, these costs plus gains are recovered through savings in material wastes and reduced labor costs. A study conducted by the National Association of Home Builders Research Center (NAHBRC) found that OVE methods saved $0.24 to $1.20 per square foot in framing wood compared with conventionally built houses (NRDC, "Efficient Wood Use in Residential Construction," 1998). | ||||||||
| Public Acceptance: | ||||||||
| The public is generally unaware of how much wood and labor goes into conventionally framed wood buildings; therefore, educating owners about the process might help them identify and appreciate the economic advantages of OVE. | ||||||||
| Regulatory: | ||||||||
| Most building codes support OVE framing techniques; however, OVE practices may be unfamiliar or new to building officials in some jurisdictions. Consulting building officials early in the design phase is recommended. | ||||||||
| Considerations: | ||||||||
(Excerpted from "Efficient Wood Use in Residential Construction," NRDC, 1998) "It is crucial to understand that OVE does not mean skimping on materials or adopting structurally inferior building practices. OVE techniques may not make sense under all circumstances they should only be adopted after close scrutiny as to their appropriateness and with adequate training of framing crews to ensure that the structural integrity and durability of the [building] are not compromised. [The applicability of OVE techniques] is also limited by four general factors: need for up-front investment, structural considerations, acceptability to building officials, and risk concerns. OVE typically requires an up-front investment in design and engineering, as well as framing crew training and supervision. The evaluation and application of OVE techniques so that they will comply with all of the various building code requirements is typically the responsibility of the architect or engineer. The design professional may be reluctant, because of a competitive industry, to include this additional cost in a proposal. It is also a cost that the builder or developer may sometimes be unwilling to pay, despite downstream savings. Structural considerations that may limit the use of OVE are entirely case-specific: size and configuration of the structure, live and dead loads, wind and seismic exposure, etc. In some instances (as with different header designs), tables in the reference publications may provide adequate design information; in others, an engineer or architect will need to be consulted. The need to involve an engineer or architect is often governed by local regulations or may be required at the discretion of the building official. In jurisdictions where building permit drawings must be stamped by an engineer or architect, the building official may allow the use of any OVE techniques that appear on the stamped drawings. However, the building official has the power to deny the use of any practices s/he deems unsafe, whether or not stamped drawings are furnished. It is advisable to consult with the building official early in the design process. Deviation from the standard practices of the industry is generally felt to be risky. Unfortunately, this can make the developer, the design team, or even the framing crew reluctant to adopt innovations, even in the face of test data or stamped engineering calculations. One tool that may be helpful in combating this hesitancy is a performance-based contract, which provides incentives for meeting specific performance goals, such as wood savings or energy efficiency. Additional limitations may apply to specific OVE techniques. For instance, some builders have reported difficulty getting exterior plywood to lie flat on studs at 24" centers. Where feasible, applying sheathing with the 8-foot dimension horizontal can help prevent wall warping; in addition, if the lowest 'course' of sheathing covers the first floor rim joist, the third course will cover and reinforce the joint between first and second floors, potentially eliminating the need for costly strapping hardware. In some cases, when spacing is increased, it may be necessary to use thicker sheathing to stiffen the diaphragm. Also, two-coat stuccos and vinyl sidings may not always be admissible on studs at 24" on center." | ||||||||
| Guidelines: | ||||||||
| Below are OVE techniques that involve both the design and construction phases. This section is intended only as an introduction to OVE methods and practices; consult code requirements and/or OVE/Advanced Framing guides for more specific requirements, descriptions, and instructions.
Design and Engineering
Optimum Value Engineering, Fig. 1
Construction
Optimum Value Engineering, Fig. 2
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| Resources: | ||||||||
| Professional Assistance: | ||||||||
How-To GuidesBuilder's Guide , Joseph Lstiburek, 1997. Builder's Manual , 1995. Cost-Effective Home Building , 1994. Efficient Wood Use in Residential Construction , Ann Edminster and Sami Yassa. Exemplary Home Builder's Field Guide , Joseph Lstiburek, 1997. Residential Construction Waste Management: A Builder's Field Guide Super Good Cents Builder's Field Guide to Energy Efficient Construction Advanced Framing CodeAdvanced Energy Efficient and Resource Efficient Single Family Residence Code (Section 326), Lake County, IL, Joseph Lstiburek and Betsy Pettit, 1996. Building Science Corporation. TrainingNational Association of Home Builders What's Working |
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| Components/Materials/Systems: | ||||||||
| Body Copy | ||||||||
| General Assistance: | ||||||||
Affordable Resource Efficiency , by Laura Armstrong Stone, 1993. Builder's Guide , Energy Efficient Building Association Building America Website: Guide to Resource Efficient Building Elements , Tracy Mumma, et al., 1997. ReCRAFT 90 , Steve Loken, 1993. Reducing Home Building Costs with OVE Design and Construction , NAHB Research Center, Inc., 1977. ToolBase Hotline Western Wood Products Association |
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