Advanced Wall Framing
Some of the techniques
described below may not be allowed under some circumstances (i.e., high winds
or seismic potential) or in some localities. Be certain to consult local
building officials early in the design phase to verify or obtain acceptance of
these techniques.
WHY USE EFFICIENT
FRAMING?
- Reduce Material Cost - buy fewer studs and top
plates, use smaller headers
- Reduce Labor And Construction Time - carry and install fewer
studs, make fewer cuts
- Save Energy - replace wood with better insulating
materials
- Save Natural Resources - less wood used = fewer
trees cut, shipped ,and processed
- Reduce Waste - less scrap from fewer cut
studs, full use of modular sheathing and drywall
- Increase Comfort - reduce or eliminate cold
surfaces
- Reduce Drywall Cracking - fewer drywall-to-framing
attachments = fewer cracks 7.
BASIC TECHNIQUES
- Two-Foot Module 1. 24-Inch On-Center (oc)
Framing 1.
- Single Top Plates 1. Properly Sized (and
insulated) Headers 1.
- Reduced Use of Cripples, Jacks, Drywall Backers
1. Insulating Sheathing 1.
Figure 1 - Two-Foot Module Figure 2 - In-Line Framing
PLANNING
Two-Foot Module - Building on a two-foot module
(Figure 1) reduces material use, labor, and waste since many products come in
multiples of two feet. For example, with proper planning, the cutoff from a
sheet of plywood cut in half can be used in full somewhere else, saving an
additional cut and eliminating waste.
In-Line Framing - This refers to aligning floor,
wall, and roof framing members directly above or below each other, allowing
direct downward transfer of loads from one to the next (Figure 2). In-line
framing allows elimination of double top plates and is often thought of in the
context of 24-inch on-center studs placed directly below roof trusses, which
are most commonly placed at 24 inches on-center.
Window and Door Layout - Windows with rough openings of
22-1/2” are available. These windows can fit between studs that are on a
standard 24” oc layout. Headers can then be eliminated with this method when
using in-line framing. For windows or doors wider than the stud spacing, only
one extra stud is required if one side of the window or door is placed against
a stud which is on the standard layout and metal header hangers are used
(Figure 2).
Other items - Careful planning of roof length
and width (i.e., altering pitch and/or overhang width) can also reduce labor,
material use, and waste (consider spacing required for ridge vent - Figure 1).
Detailed plans that indicate the presence of each piece of wood, cross bracing,
etc. in the house and locations for all other items such as wiring, ducts, and
pipes can eliminate conflicts over space, speed installation, and eliminate the
need to alter or move studs, joists, etc. later.
FRAMING
Stud Spacing -In many cases, increasing stud
spacing from 16 inches oc to 24 inches oc is structurally acceptable and
accepted by codes. The CABO One- and Two-Family Dwelling Code allows the
following for studs up to 10 feet long:
Lumber plus labor costs for 2x6 @
24” oc are similar to those for 2x4 @ 16” oc. 2x6 @ 24” oc walls allow more
cavity insulation but will require extension jambs (unless drywall returns are
used). Also consider 2x4 @ 24” oc walls with foam sheathing when allowed.
Single Top Plates - If used in conjunction with
in-line framing, single top plates are usually acceptable from a structural
standpoint, and accepted by model building codes such as CABO and BOCA. These
codes require that 3”x 6”, 0.036-inch-thick (20 Ga.) galvanized steel plates be
nailed across wood plate joints with three 8d nails at each side (Figure 3).
Backer
Single top plates affect sheathing
and drywall needs and installation due to changed wall height. In some areas,
94-1/4” studs (often used for interior walls) are available that allow
installation of sheathing and drywall without cutting. Use of 96” studs
necessitates cutting to length or adding a strip of drywall at the bottom of
the wall. Pre-cut 92-5/8” studs will require “ripping” approximately 1” off the
sheathing and drywall. If 94-1/4” studs are not available, using 92-5/8” studs
requires the least labor and creates the least waste.
Jacks (shoulder studs/cripples)-Jacks can be eliminated when
structural headers are eliminated or when metal hangers, such as shown in
Figure 7, are used to support structural headers. Elimination of jacks reduces
the available nailing area for siding and trim if nailable sheathing (plywood
or OSB) is not used - there may be as little as 1-1/2 inches of nailable width
next to a window. If needed, a wood backer may be installed behind the
sheathing.
Outside and Inside Corners -Corners can be framed to decrease
lumber use and enable more complete insulation, compared to typical practice
(Figures 4 & 5). Attachment of exterior trim and siding at corners should
be considered if nailable sheathing is not used. For example, vinyl-siding
corners require nailing at a point several inches from the corner. If foam or
other non-nailbase sheathing is used, it may be necessary to add a wood nailer
behind the sheathing.
When drywall clips are used, they
should be installed above the level of the interior trim so trim nails will not
hit them. The non-coped trim piece should be installed first, against the
drywall that bears on the clip, so that the final coped trim piece can be
nailed to the stud.
Partition Connections to Exterior
Walls (T’s) - These
are often made by adding studs at each side of the partition, which serve only
to attach drywall. In addition to wasting wood, this creates an area that is
very hard to insulate. Alternatives include installing “ladder blocks” (Figure
6), drywall clips, or a full length 2x6 or 1x6 behind the first partition stud.
Intermediate Blocking - Installing horizontal blocks
between studs is generally not required for structural strength or fire/draft
stopping in platform framing, at least with standard eight foot high walls.
Headers -Structural headers are often
oversized or installed where not needed, largely for convenience. Properly
sizing headers allows better insulation and saves wood. In some cases,
single-ply (single 2x6, for example) headers can be used, allowing even better
insulation. Headers are not required in non-bearing walls, including most
interior walls and gable-end walls with only non-bearing trusses directly
above. The following table and accompanying language outlines some header
requirements in the 1995 CABO code:
a Also applies to nominal 4-Inch single headers.
Based on No. 2 lumber with 10-foot tributary loads. Not to be used where
headers support concentrated loads.
b Load-bearing headers are not required in interior
or exterior nonbearing walls. Single flat 2-inch-by-4-inch members may be used
as headers in interior or exterior nonbearing walls for openings up to 8 feet
in width if the vertical distance to the parallel nailing surface above is not
more than 24 inches. For such nonbearing headers, no
cripples or blocking are required above the header.
Insulated headers are
possible by using foam sheathing as a spacer in place of plywood or OSB, either
between or on one side (preferably exterior) of doubled headers. This is an
excellent way to re-use scrap foam sheathing, reducing waste. For assistance in
designing headers, consult local structural engineers, code officials, lumber
suppliers, or others such as the Western Wood Products Association (WWPA).
SHEATHING
OSB or plywood
sheathing is typically used to provide racking resistance to walls (lateral
resistance to wind or seismic loads). Often, some other type of sheathing is
used to cover the remainder of the framing. One way to increase the insulating
value of a wall is to replace non-insulating sheathing with insulating (foam)
sheathing, while still providing racking resistance by one of the following
methods:
- Use structural sheathing at corners and
intermediate points as required (typically every 25 feet), with foam
sheathing at all other locations.
- Use thin, structural paperboard sheathing at
corners, covered completely with foam sheathing.
- Use full foam sheathing with cross bracing
(flat metal straps, let-in T-shaped metal straps, or let-in wood 1x’s).
Note that the choice
of sheathing impacts the ability to nail siding and affects the air leakage and
moisture performance of the wall assembly.
GRAPHICS
All of the graphics
for Advanced Wall Framing come from the Building Science Corporation (Boston,
MA) and are being used with their permission.
FOR MORE INFORMATION
NAHB Research Center: sells Cost-Effective
Home Building and EEBA Builder’s Guides (series of practical books
for various climates). Contact their HOMEBASE SREVICES Hotline: 800-898-2842;
http://www.nahbrc.org;
homebase@nahbrc.org
Energy Efficient
Building Association: P.O. Box 22307, Eagan, MN 55122. 651-994-1536; http://www.eeba.org
Southern Pine Council: P.O. Box 641700,
Kenner, Louisiana 70064. 504-443-4464;
Southface Energy
Institute: 241 Pine Street, Atlanta, Georgia 30308. 404-872-3549; http://www.southface.org
Western Wood Products
Association: 522 SW Fifth Ave., Suite 500, Portland, Oregon 97204.
503-224-3930; http://www.wwpa.org
Fact Sheet Source
The material provided
in this fact sheet comes from Appendix J of the National Association of Home
Builders Research Center’s “A Guide to Developing Green Builder Programs” and
is used with their permission.