Most builders use plywood or OSB sheathing to laterally brace
their framed walls and typically feel comfortable when they
have a full sheet at both ends of the wall. I suspect that
feeling is based more on intuition than on calculated strength,
but most of the time it works. The plywood prevents the studs
from racking and folding over, while nails through the bottom
plate and hold-down straps prevent sliding and uplift from wind
But what about walls with large openings and not much room for
sheathing on each side? The most common example is the garage
wall with, say, an 18-foot overhead door and two 16-inch walls
at each side.
It's not difficult to prevent the wall from sliding using
anchor bolts; the sliding forces at the plate are fairly small.
The anchor bolts might also prevent uplift, but what about the
racking issue? We no longer have a full sheet of sheathing at
each end — only a 16-inch-wide strip. Considering the
gaping hole for the garage doors, it's hard to imagine that a
strip of sheathing would provide adequate lateral
But, in fact, if they're built properly, those 16-inch end
walls can provide the needed lateral strength. When it comes to
the engineering calculations, APA has done the heavy lifting
for us, having tested and documented a method they refer to as
the Narrow Wall Bracing Method (see Figure 1). Using this
approach, builders can develop the required lateral bracing in
walls with end panels as narrow as 16 inches.
Figure 1.APA determined the nailing schedule for
the Narrow Wall Bracing Method by building the assembly and
testing it under measured loads.
The best news about the APA approach is that it requires no
exotic connectors or expensive materials. The entire system can
be built using off-the-shelf materials. The APA method does
require that you pay close attention to details, however
— details that likely differ from the way you're used
to building garage end walls.
Sizing the Header
When faced with a long span, builders typically double or
triple the cripple studs, and while that provides additional
bearing for the ends of the header, it adds no lateral strength
to the wall system. In the Narrow Wall Bracing Method, the
header must extend to the end of the wall (minus 1 1/2 inches
to allow for a king stud on each end).
Extending the header like that increases the available
fastening area where the narrow wall sheathing overlays the
header, a critical element in developing the needed lateral
strength. The header must be built using at least two 2x12s.
Solid-sawn headers, glulams, and built-up LVLs are also
acceptable as long as they're at least 11 1/4 inches deep and 3
When framing the narrow walls at either end, you start with an
outside king stud, with a single jack fastened to the king stud
and another pair of jacks at the edge of the garage door
opening. Also, make sure to frame the narrow walls so they run
by the side walls at the corner. This allows the sheathing on
the side walls to lap the edges, which ties the corners of the
garage door wall to the side walls.
To prevent the header from rolling toward the outside of the
wall, you have to install two 1,000-pound tension straps
connecting the header to the double cripple studs next to the
door opening (Figure 2). These connectors are available at most
lumberyards; just make sure that the strap is rated for at
least 1,000 pounds in tension, and that you use the right
number of fasteners to develop the required strength.
Figure 2.A 1,000-pound tension strap on the back
side of the header prevents the header from rolling off the
supports under load.
The minimum allowable sheathing is 3/8-inch structural-rated
plywood. Both 7/16-inch OSB and 15/32-inch exterior structural
plywood — the most common sheathings in my area
— are therefore acceptable. The sheathing must run
from the bottom of the sill plate to the top of the header but
does not have to be "L cut" around the header — the
way you would typically install sheathing or interior drywall.
It's okay to L-cut the sheathing, but no lateral strength gain
is recognized. In cases where the narrow wall is taller than 8
feet, you must piece the plywood so the joint is located within
24 inches of mid-height in the narrow wall.
The maximum hole size in the sheathing is 7/8 inch, so be sure
you consider any penetrations in the narrow wall area
(electrical boxes, for example). The sheathing on the return
walls must completely cover the king stud at the corner.
Nails, Nails, and More Nails
The heart of the Narrow Wall Bracing Method is the nailing
schedule. The top plate of the narrow walls gets two rows of
16d sinker nails (0.148-inch diameter x 3 1/4 inches long) 3
inches on-center. The end stud on the return wall is fastened
to the narrow-wall king stud and double cripple studs with two
rows of 16d nails at 24 inches on-center. Nail the narrow wall
sheathing 3 inches on-center using 8d common nails
(.131-inch-diameter shank x 2 1/2-inch length). The sheathing
lapping the ends of the narrow walls should also be nailed with
8d commons, every 6 inches. Keep in mind that nail heads must
be flush with the sheathing. Overdriven nails compromise the
To resist the uplift forces, two 1/2-inch anchor bolts are
installed for each narrow wall section. The bolts should be
located 1 1/2 inches from the doubled cripple studs to provide
enough room for the required 2x2x3/16-inch plate washers. Don't
cheat and use standard 1/2-inch round washers: The square
washers provide approximately three times more hold-down area
— a critical detail when uplift loads start to ratchet
up (Figure 3). These washers are standard issue in seismic
areas and are readily available from connector manufacturers.
The anchor bolts should be imbedded in the foundation at least
7 inches. When using a single bottom plate, you'll need an
anchor bolt that's at least 10 inches long.
Figure 3.Standard anchor bolts and 3/16-inch-thick
square washers available from metal connector manufacturers
secure the narrow wall to the foundation stem
The minimum width of the narrow end walls is governed by the
height of the top of the header. The APA recommended ratio is 1
to 6. For example, an 8-foot-tall wall — measured at
the top of the header — requires a minimum 16-inch end
wall (16 x 6 = 96). A 10-foot wall — the maximum
allowable — requires a minimum 20-inch end