Variations on Wood Light Frame Construction


The 2 _ 4 (38 _ 89 mm) has been

the standard-size wall stud since

light framing was invented. In recent

years, however, pressures for heating

fuel conservation have led to energy

code requirements for more thermal

insulation than can be inserted

in the cavities of a wall framed with

members only 3½ inches (89 mm)

deep. One solution is to frame walls

with 2 _ 6 (38 _ 140 mm) studs,

usually at a spacing of 24 inches (610

mm), creating an insulation cavity 5½

inches (140 mm) deep. Alternatively,

2 _ 4-framed walls may be covered

either inside or out with insulating

plastic foam sheathing, thus reaching

an insulation value about the

same as that of a conventionally insulated

2 _ 6-framed wall. For even

greater insulation performance, 2 _

6 studs and insulating sheathing may

be used in tandem. Alternatively, in

very cold climates, even deeper wall

assemblies that can achieve greater

insulation values may be constructed

of two separate layers of wall studs

or of vertical truss studs made up of

pairs of ordinary studs joined at intervals

by plywood plates.

Usage

In wood light frame structures constructed

with advanced framing techniques

(also called optimum value engineering),

special attention is given to

minimizing the use of redundant or

structurally unnecessary wood members,

thereby reducing the amount

of lumber required to construct the

frame and, once the frame is insulated,

increasing its thermal ef ciency

A variety of techniques

may be used, including:

¥ Spacing framing members at 24

inches (610 mm) rather than 16 inches

(406 mm) o.c.: Wider spacing of framing

members reduces the amount of

lumber required. In exterior walls,

thermal ef ciency is also improved

by the reduction in thermal bridging

area in comparison to walls framed

with more closely spaced members.

¥ Designing to a 24-inch (610-mm)

module: When the outside dimensions

of a framed structure conform

to a 24-inch module, sheathing panel

waste is minimized. Planning rough

opening sizes and locations in ß oors,

walls, and roofs to conform, where

possible, to modular dimensions can

reduce waste even further. Designing

to modular dimensions also reduces

wastage of interior wallboard.

¥ Using single top plates in all walls,

both bearing and nonbearing: In the

case of bearing walls, this requires

ß oor or roof framing members to

align directly over studs in the walls

that support them.

¥ Minimizing other unneeded

framing members: DonÕt use headers over openings in nonbearing walls,

since they are not needed; in bearing

walls, use headers only as deep as

required for the loads and span.

Where corner studs serve only to

provide nailing surfaces or support

for wallboard, use other, less wasteful

blocking techniques or metal clips

designed for this purpose instead.

Replace jack studs supporting headers

at window and door openings

with metal hangers; eliminate unneeded

cripple studs under rough

sills. All of these techniques save lumber

and, in exterior walls, increase

energy ef ciency by reducing thermal

bridging through solid framing

members.

¥ Eliminating unneeded plywood

and OSB wall sheathing: Where letin

bracing is structurally adequate

for lateral force resistance, eliminate

structural panel wall sheathing entirely

and cover walls with insulating

sheathing for better thermal ef -

ciency. Where structural panels are

required, use the minimum extent of

panels necessary.

Advanced framing techniques

rely on unconventional framing

methods and signi cantly reduce

redundancy in the building frame.

For these reasons, they should not

be used without guidance from a

structural engineer or other quali

ed design professional, and special

review and approval from local building

authorities may be required. Nevertheless,

where these techniques

are used, signi cant bene ts can be

realized. According to the National

Association of Home Builders Partnership

for Advancing Technology

in Housing, advanced framing techniques

can reduce the amount of

lumber used in a wood light frame

structure by up to 19 percent and

improve the energy ef ciency of the

insulated structure by as much as 30

percent.

 


 

Figure 5.65

Roof trusses are typically lifted to the roof by a

boom mounted on the delivery truck. This is one

of a series of identical attic trusses, which will

frame a habitable space under the roof. (Photo by Rob Thallon)



Roof trusses, and to a lesser extent fl oor trusses, are used in platform frame buildings because of their speed of erection, economy of material usage,

and long spans. Though many ß oor trusses are light enough to be lifted and installed by two carpenters, most truss assemblies are erected with the

aid of a small crane that often is attached to the truck on which the trusses are delivered (Figure 5.65). Roof trusses are particularly slender

in proportion, usually only 1½ inches (38 mm) thick and capable of spanning 24 to 32 feet (7.5 to 10 m). They must be temporarily braced during

construction to prevent buckling or the dominolike collapse of all the trusses until they are adequately secured permanently by the application

of roof sheathing panels and interior nishes (Figure 5.66). Manufactured wall panels have been adopted more slowly than roof

and ß oor trusses, and are used mostly by large builders who build hundreds or thousands of houses per year. For the smaller builder, wall framing can

be done on site with the same amount of material as with panels and with


 

Figure 5.66 A roof framed with prefabricated trusses. Approximately midway up the upper chords of the trusses, temporary strapping ties the trusses to one another for bracing. Other diagonal bracing, not visible in this photograph, ties the trusses to floor or ceiling framing to prevent the entire row from collectively tipping sideways. (Photo by Joseph Iano)

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