Minimum Wall Studs

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ENERGY STAR Version 3, (Rev. 07)

Thermal Enclosure Checklist, Reduced Thermal Bridging. Reduced thermal bridging at above-grade walls separating conditioned from unconditioned space (rim / band joists exempted) using advanced framing. Minimum stud spacing of 16” o.c. for 2x4 framing in all Climate Zones and, in Climate Zones 5 through 8, 24” o.c. for 2x6 framing unless construction documents specify other spacing is structurally required.

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International Energy Conservation Code (IECC) Climate Regions

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Description

Adding more studs than necessary wastes lumber and reduces the wall’s thermal resistance because the lumber blocks cavity space that could be filled with insulation and because each stud represents a thermal bridge that can transfer heat between the interior and exterior of the building. Wood-framed houses have traditionally been built with 2x4 studs spaced 16-inches on-center. Research has shown exterior framed walls can be adequately supported by 2x6 studs spaced 24-inches on-center. This wider spacing reduces the number of studs in the wall, thus reducing thermal resistance and increase the amount of space available for insulation. Building walls of 2x6s 24-inch on-center has long been permitted in building codes in most jurisdictions, and is particularly appropriate for colder climates (IECC Climate Zones 5-8) where higher wall R-values are required (Baczek, Yost, and Finegan 2002; DOE 2002; Lstiburek 2010). In some jurisdictions, particularly in hurricane zones, 16-inch on-center is the maximum stud spacing allowed; check with local code officials.

This 2x6, 24-inch on-center stud spacing is one of many components of advanced wall framing that reduce costs and provide materials and energy savings. Techniques for installing 24-inch on-center exterior and interior wall framing and single top plates are described below. Other techniques are described in other resource guides: see Insulated Corners, which explains how to construct corners with 2 studs instead of 3 studs to permit more insulation, Insulated Headers for tips on how and when to build open and insulated headers over windows and doors, Minimal Framing at Doors/Windows for efficient framing around doors and windows, and Insulated Interior/Exterior Wall Intersections for ways to reduce framing and add insulation where interior walls intersect exterior walls.
 
In one study employing several advanced framing techniques, such as 2x6 24-inch on-center wall framing, 24-inch on-center floor joist and rafter spacing, 2x4 24-inch on-center interior framing, 2-stud corners, open and insulated headers, reduced studs around windows and doors, and single top plates, all of the measures combined contributed to energy savings of 13% over standard framing but this single measure alone  - switching from 2x4 16-inch on-center to 2x6 24-inch on-center framing– accounted for energy savings of 11% (Lstiburek and Grin 2010). The energy savings is accounted for by two factors – the thicker wall enables wall insulation to be upgraded from R-13 to R-19 and less studs mean less thermal bridging.

Building scientists suggest that builders should consider the “whole-wall” R-value as opposed to the center-of-cavity or rated R-value of the insulation. In one study, a 2x4 16-inch on-center wall was insulated with batts labeled R-13, but researchers calculated the actual whole-wall insulation value of the wall at R-9.4 (or 72% of R-13) when the thermal conductivity of the framing, windows, and doors are taken into account. In the same simulation, researchers found that the calculated whole-wall R value of a 2x6 24-inch on-center wall insulated with R-19 batts, was R-15.2, or 80% of R-19 (Baczek, Yost, and Finegan 2002). While both walls had a lower whole-wall R-value than rated R-value, the 2x6, 24-inch on-center wall with R-19 performed closer to its rated R-value because the wall had less thermal bridging.

Stud spacing can also affect cost savings. In one study of a 2,910-square foot home, switching from 2x4 16-inch on-center framing to 2x6 24-inch on-center framing reduced board feet of lumber by 1,634 feet and cut costs by $171. When other advanced framing measures were added, like switching to single top plates, 24-inch spacing of interior walls, and open headers, lumber costs were reduced $1,117 (Baczek, Yost, and Finegan 2002).

Framing on a two-foot also saves money by reducing material waste. Most sheet goods (plywood, OSB, foam insulation) come in 4x8-foot sheets. When the entire home is designed on a 2-foot grid from roof rafters to wall framing to floor joists, sheet good and lumber waste are greatly reduced. Reducing the number of studs in the walls by one-third also reduces labor costs in terms of the time it takes to handle, cut, install, drill through, and attach to studs. Based on numerous field experiments, Building Science Corporation estimates savings of up to $1,000 per home in materials and labor are possible for production builders who use a combination of advanced framing techniques (Lstiburek and Grin 2010).

Advanced framing techniques should be specified in the framer’s contract. Detailed framing elevations should be prepared after confirming that these advanced framing techniques are permitted by code in the local jurisdiction. There is a cost associated with redrawing existing floor plans or providing framing details for new plans, but the cost per home is minimal if the plan will be used several times. Also, cost savings will be realized because the details will help gain building official approval, improve accuracy for materials purchasing, clarify instructions for the lead framer, assist in training subs, and greatly improve the chances that the specified measure will actually be implemented (Baczek, Yost, and Finegan 2002).

Advanced framing uses less wall studs

Figure 1 - Traditional framing of stud-framed walls with 2x4 studs spaced 16-inches on-center uses more wood than necessary and limits the amount of insulation that can be installed. Advanced framing uses as 2x6 24-inch on-center wall framing, single top plates, and no more studs than are structurally needed, providing a dimensionally thicker wall with more space for insulation. Reference

Advanced Framing technique

Figure 2 - This house is being built with advanced framing techniques including 2x6 24-inch on-center wall framing, single top plates, open headers over windows on non-load-bearing walls, and minimal studs around windows. Reference

How to Construct Walls with Fewer Studs

  1. Design homes on a two-foot grid with 2x6 studs spaced 24-inches on-center. Align rafters, wall studs, and floor joists so that the load is transferred and adequately supported to allow installation of single top plates. Align windows and doors with this two-foot stud spacing to reduce the number of extra king studs needed. [See Minimal Framing at Doors/Windows.]
  2. Specify single top plates in framing elevations. For an 8-foot wall, don’t purchase standard precut 92.5-inch studs, purchase 8-foot (96-inch) studs and cut them to 94 inches (Lstiburek 2010).

Advanced framing details throughout house limit use of lumber

Figure 3 - Advanced framing details throughout the house minimize the use of lumber. Reference

  3.  Connect top-plates using either a metal plate or a wood splice.  

A metal plate is used to connect top plates to one another

Figure 4 - Single top plates can be connected with a metal plate. Reference

Wood blocking is used as a splice to connect top plates together

Figure 5 - Single top plates can be connected with a splice. Wood blocking is used as a splice to connect the top plates together. The “middle” stud is cut shorter to accommodate the wood splice. Reference

  4.  For interior walls, specify 2x4 studs placed 24-inch on-center with single headers. Non-structural connectors can be installed for non-load-bearing interior walls.

Interior non-load bearing walls are 2x4 studs spaced 24-inchon- center, can have non-structural connectors

Figure 6 - Interior walls are made of 2x4 studs spaced 24-inch on- center. If they are non-load bearing, they can have non-structural connectors. Reference

Ensuring Success

Advanced framing details should be specified in the construction plans (i.e., framing elevations should be provided) and reviewed with framers. The construction supervisor should ensure that framing crews are knowledgeable of or trained in advanced framing techniques. The framing should be visually inspected by the site supervisor before electrical, plumbing, HVAC, and drywall are installed.

Scope

Minimum stud spacing of 16 inch o.c. for 2x4 walls in all Climate Zones and, in Climate Zones 5 through 8, 24 inch o.c. for 2x6 framing unless construction documents specify other spacing is structurally required

Reduced Thermal Bridging

Minimum stud spacing of 16-inch on-center for 2 x 4 walls in all climate zones; and in climate zones 5 through 8, 24-inch on-center for 2 x 6 framing.

  1. 16 inches for 2 x 4 framing on center in all climate zones.
  2. 24 inches for 2 x 6 framing on center in climate zones 5 to 8.

ENERGY STAR Notes:

All items of 4.4.5a-4.4.5e of the ENERGY STAR Thermal Enclosure System Rater Checklist must be installed to comply with ENERGY STAR.

Mass walls utilized as the thermal mass component of a passive solar design (e.g., a Trombe wall) are exempt from this Item. To be eligible for this exemption, the passive solar design shall be comprised of the following five components: an aperture or collector, an absorber, thermal mass, a distribution system, and a control system. See DOE's guidance for passive solar home design.

Mass walls that are not part of a passive solar design (e.g., CMU block or log home enclosure) shall either utilize the strategies outlined in Item 4.4 (of the ENERGY STAR Thermal Enclosure System Rater Checklist). Or, the pathway in the assembly with the least thermal resistance, as determined using a method consistent with the 2009 ASHRAE Handbook of Fundamentals, shall provide >= 50% of the applicable assembly resistance, defined as the reciprocal of the mass wall equivalent U-factor in the 2009 IECC – Table 402.1.3. Documentation identifying the pathway with the least thermal resistance and its resistance value shall be collected by the rater and any Builder Verified or Rater Verified box under Item 4.4 (of the ENERGY STAR Thermal Enclosure System Rater Checklist) shall be checked.

Up to 10% of the total exterior wall surface area is exempted from the reduced thermal bridging requirements to accommodate intentional designed details (e.g., architectural details such as thermal fins, wing walls, or masonry fireplaces; structural details, such as steel columns). It shall be apparent to the Rater that the exempted areas are intentional designed details or the exempted area shall be documented in a plan provided by the builder, architect, designer, or engineer. The rater need not evaluate the necessity of the designed detail to qualify the home.

In Climate Zones 5 - 8, a minimum stud spacing of 16-inch on-center is permitted to be used with 2x6 framing if >= R-20.0 wall cavity insulation is achieved. Regardless, all vertical framing members shall either be on-center or have an alternative structural purpose (e.g., framing members at the edge of pre-fabricated panels) that is apparent to the rater or documented in a framing plan that encompasses that member and is provided by the builder, architect, designer, or engineer. The rater need not evaluate the structural necessity of the framing plan to qualify the home. However, all 2x6 framing with stud spacing of 16-inch on-center in Climate Zones 5 - 8 shall have >= R-20.0 wall cavity insulation installed regardless of any framing plan or alternative equivalent total UA calculation.

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Compliance

ENERGY STAR Version 3, (Rev. 07)

Thermal Enclosure Checklist, Reduced Thermal Bridging. Reduced thermal bridging at above-grade walls separating conditioned from unconditioned space (rim / band joists exempted) using advanced framing. Minimum stud spacing of 16” o.c. for 2x4 framing in all Climate Zones and, in Climate Zones 5 through 8, 24” o.c. for 2x6 framing unless construction documents specify other spacing is structurally required. In Climate Zones 5 - 8, a minimum stud spacing of 16-inch on-center is permitted to be used with 2x6 framing if >= R-20.0 wall cavity insulation is achieved. Regardless, all vertical framing members shall either be on-center or have an alternative structural purpose (e.g., framing members at the edge of pre-fabricated panels) that is apparent to the rater or documented in a framing plan that encompasses that member and is provided by the builder, architect, designer, or engineer. The rater need not evaluate the structural necessity of the framing plan to qualify the home. However, all 2x6 framing with stud spacing of 16-inch on-center in Climate Zones 5 - 8 shall have >= R-20.0 wall cavity insulation installed regardless of any framing plan or alternative equivalent total UA calculation.

DOE Challenge Home

Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3.

2009 IECC

This topic is not specifically addressed in the 2009 IECC.

2009 IRC

This topic is not specifically addressed in the 2009 IRC.

2012 IECC

This topic is not specifically addressed in the 2012 IECC.

2012 IRC

This topic is not specifically addressed in the 2012 IRC.

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References and Resources*

  1. Author(s): U.S. Department of Labor
    Organization(s): U.S. Department of Labor
    Publication Date: January 2012

    Website with information about advanced framing techniques.

  2. Author(s): Baczek, Yost, Finegan
    Organization(s): BSC
    Publication Date: August 2002

    Report describing approaches to using less wood in home building that minimize waste.

  3. Author(s): NAHB, Southface Energy Institute, ORNL, NREL
    Organization(s): NAHB, Southface Energy Institute, ORNL, NREL
    Publication Date: January 2002

    Information sheet about advanced wall framing.

  4. Author(s): Lstiburek, Grin
    Organization(s): BSC
    Publication Date: November 2010

    Report investigating implementation of advanced framing in both production and prototype built homes built in a variety of climate regions across the USA.

  5. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: February 2010

    Report detaining advanced framing techniques, including discussion of cost and energy savings.

  6. Author(s): DOE
    Organization(s): DOE
    Publication Date: June 2013

    Standard requirements for DOE's Challenge Home national program certification.

  7. Author(s): EPA
    Organization(s): EPA
    Publication Date: June 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  8. Author(s): EPA
    Organization(s): EPA
    Publication Date: October 2011

    Guide describing details that serve as a visual reference for each of the line items in the Thermal Enclosure System Rater Checklist.

Last Updated: 08/15/2013

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