The evolving rules for wall bracing have become perhaps the most
complicated part of the prescriptive International Residential
Code. Some builders point out that you can simplify your life by
viewing the choices in a black-and-white way: Either stick to small
houses with simple, boxy shapes (and keep your doors and windows
away from the corners); or, hire an engineer.
When your design wind speeds are above 110 mph, you have no choice:
Engineered design is mandatory (although there are some
"deemed-to-comply" guidebooks available that let the engineers
follow simple recipes). And for homes in wind speed zones below 110
mph, the prescriptive code does actually offer a lot of
flexibility. But if you want to play around with window locations
or sheathing types in the prescriptive IRC, there's a lot to
Let's take a look at just one example. The 2009 IRC will allow
builders to mix wall bracing types on a single building -- so for
example, one wall might have plywood sheathing on the whole wall,
while another wall might have let-in bracing and foam sheathing.
But the wall that's fully sheathed needs to be anchored at the
ends. One way to anchor those ends is with a short, 24-inch plywood
or OSB-sheathed return wall at the corner.
The code books provide a plan-view drawing that explains how that
corner has to be constructed.
Against moderate wind force, that corner is enough to hold down the
end of the wall to prevent overturning or uplift.
But suppose that wall around the corner isn't sheathed, or suppose
you want a door or window at that corner, closer than 24 inches
from the wall end? Now you don't have the requisite anchoring. So
the code gives you another option: You can place an
800-pound-capacity hold-down — an engineered anchor that is
embedded into the concrete and fastened to the side of a wall stud
— at the specified location, to replace the anchoring power
of the framed corner.
Under certain circumstances, you don't have to place that hold-down
right at the wall end. You can also put the hold-down at other
places in the braced wall line.
In the 2009 version of the IRC, the value of those 800-pound
hold-downs is recognized in another way. For fully sheathed
buildings, adding the hold-downs allows you to reduce the required
amount of wall bracing in a braced wall line — because the
presence of the hold-downs increases the power of short plywood or
OSB-sheathed wall segments to stiffen the building.
It's not simple. It's complicated, and it's fussy. It's also easy
to make mistakes — move a door or a window half a foot, and
you've gone over the line and you might fail the plan review.
Builders, especially if they build large, complicated, expensive
houses, might reasonably conclude that it's worth it to just bite
the bullet from the outset and hire an engineer, then use
engineered design with formal shearwalls to meet their bracing
On the other hand, if you take the time and trouble to learn the
complicated rules, you may find many cases where meeting the
prescriptive standard in the IRC saves time and money as compared
to the engineered solution. Here's another resource for learning
about the rules: a PowerPoint
PDF posted on the website of Henrico, Virginia. (Virginia has
already incorporated the 2007 IRC supplement, which includes most
of the upgrades coming in the 2009 IRC, into their statewide
Even building inspectors don't find the new rules easy to manage.
Simpson Strong-Tie engineer Randy Shackelford has been traveling
the country educating building department officials on the bracing
rules. On March 23 and April 26-29, 2009, Shackelford will be in
Massachusetts teaching building officials (the state has only
recently implemented the 2006 IRC). In a recent phone interview,
Shackelford said most Simpson
hold-downs have capacities well beyond the 800 pounds required
for the augmenting braced wall panels. The advantage of the new
800-pound requirement, he points out, is that it simplifies the
attachment point to the concrete foundation. "It's such a
light-duty connection," he says, "that the anchorage to the
foundation is easier. It doesn't take an epoxy adhesive. In a lot
of the country, they're not going to know where these things go
until the framers lay out the walls, and so they are going to want
to retrofit the anchorage. And for that, we have our new Titen
HD's, where you can just drill the hole and screw them in. It's not
like an expansion anchor that might have special problems right
next to the edge of the concrete, and it's not like you need any
special tools, like for injecting epoxy — since the capacity
we need is so low."
Shackelford also suggested builders take a look at a new Simpson
light-duty hold-down, the DTT2Z. The new connector was
originally designed to provide a through-bolted attachment for
connecting deck posts to deck frame joists, but Shackelford says it
also works well for holding down braced wall segment ends or house
The large hole in the base of Simpson's new DTT2Z connector
receives a concrete anchor bolt. The smaller holes are for
attaching the hardware to a wall stud, for which Simpson specifies
it's load-rated "Strong Drive" hex-head screws.