Retrofitting an Engineered Shear Panel - Continued
The demo work was pretty simple; the wall contained some
electrical wiring but no plumbing or ducts. We rerouted the
electrical and removed the existing studs by cutting them off
at the elevation of the new header. The last step —
removing the subflooring from the areas where the panels would
sit — gave us the access we needed to drill holes for
anchor bolts and to install new joist blocking.
Installing the Header
The header was to run the full length of the wall and rest on
jack studs at either end. The shear panels would sit directly
on the floor framing and be blocked tight to the header
Our first task was to lift the 6x12 header into position. To
avoid wrenching our backs, we hung a block and tackle from an
eyebolt we'd put in the wall and used it to hoist the header
most of the way (Figure 5). When the header got close, we used
our shoulders to lift one end onto a jack stud. We lifted the
other end the same way, but because cripple studs were now
bearing down on the new header from above, we had to angle the
jack stud under the header and persuade it into position with a
sledgehammer. This brought the header tight to the bottom of
the cripple studs, where we secured it with nails.
Figure 5. The crew used
a block and tackle (top) to hoist the header high enough to get
a worker's shoulder under one end and lift it onto a jack stud.
With cripples bearing down on the header along its span, it was
necessary to wedge the other end of the header into position by
beating the angled jack stud in with a sledge
At this point, the header was carrying the vertical load, but
the wall still lacked the necessary lateral stability.
New Anchor Bolts
Shear panels come in a variety of sizes. The ones we used were
18 inches wide by 92 inches tall and 3 1/2 inches thick; other
brands come in both 3 1/2- and 5 1/2-inch thicknesses.
The design called for two hold-down bolts (7/8-inch threaded
rod) per panel to be embedded 18 inches into the foundation
stem wall and glued in place with epoxy. With the supplied
template, we marked the location of the bolts and used a rotary
hammer to drill the required 1-inch holes.
Partway in, we hit rebar. In other circumstances, we might have
shifted the holes, but the bolts for a shear panel must be in
precise locations. So, to get through the rebar, we used one of
the special rebar-cutting bits sold by Simpson (Figure
Figure 6. The crew hit
rebar while drilling holes for new anchor bolts. Since moving
the holes was not an option, they used this special rebar
drilling bit from Simpson to cut through the
Stronger blocking. Before drilling
holes in the stem wall, we had removed the existing 2x8 joist
blocking from under the areas where the panels would go. This
was necessary for a couple of reasons: The blocking would
interfere with drilling, and the blocks would not be strong
enough to resist the crushing force of the panels when the
bolts were tightened.
Once the holes were drilled, we replaced the 2x8 blocks with
stronger pieces of 6x8 Parallam. The blocks, too, were drilled
so that the anchor rod could fit through.
Special inspection. In new
construction, anchor bolts are positioned before the foundation
is poured, so the inspector can see if they are properly
installed. In retrofits, however, the anchors are epoxied into
drilled holes, which makes it hard to know how strong the
connection actually is.
Our local building department requires a special inspection to
verify that new anchor bolts are securely attached. One option
is to hire an inspection company to perform pull tests on bolts
after they are installed. Instead, we verified the installation
by having the engineer — McCleary — come to the
site to watch us do the work.
First, he measured the holes to make sure they were the right
depth. After that, we used a Simpson hole-cleaning brush
(basically a wire bottlebrush) to knock loose material from the
sides of the holes. Then we used a copper pipe connected to a
shop vac to vacuum out the debris. We finished by blowing out
the holes with a second pipe connected to a compressed air
Gluing in the rods. Next, we used a special
mechanical "caulking" gun to pump a two-part Simpson adhesive
(Epoxy-Tie Set) into the holes. At McCleary's request, we
inserted the rods and jiggled them up and down to clear air
bubbles. We also twisted them in the holes make sure they were
completely coated with epoxy (Figure 7). In a couple of cases,
we temporarily removed the rods and pumped in more
Figure 7. The rod on the
right has already been installed through Parallam blocking and
into an 18-inch-deep hole in the concrete foundation below. The
glue-coated rod on the left was just removed from its hole so
that the author could pump in an additional load of
Once the adhesive was ready, we simply inserted the rods
— all the way to the bottom of the holes — and left
them alone until the epoxy set. McCleary provided us with a
document for the building department stating that the anchors
were installed as designed and in accordance with the epoxy
Attaching the Panels
The following day, we installed the panels. We began by
dropping a thick steel bearing plate over each pair of rods.
The bearing plates (supplied by the manufacturer) are necessary
when you install Hardy's panels over raised floor systems. Each
plate extends a few inches beyond the left and right sides of
the panel and has holes through which you are required run a
specified number of 1/4-inch-diameter wood screws. The screws
prevent the wall from sliding horizontally, and the anchor
bolts resist overturning.
Once the plates were installed, we stood the panels up over the
bolts (Figure 8); as expected, the panels stopped a few inches
short of the header.
Figure 8. A carpenter
places a required steel bearing plate (top) over anchor rods
glued in the previous day. The panel will fit over the rods and
land on the plate. At right, the crew wedges the top of the
panel against solid blocking on the underside of the
We could have eliminated this gap by ordering taller,
custom-sized panels, but that would have delayed the job.
Instead, we used stock panels and packed the space above with
2-by blocking before screwing through to the header from inside
the panels. This is permissible within specified limits, which
vary by brand and model. McCleary told us to use Simpson's
self-drilling SDS screws — 6-inch screws in the header
above and 41/2-inch screws in the joists and blocking below
Figure 9. In this view
down the open side of the shear panel, the installation is
complete; nuts and washers are on the anchor rods, and screws
pass through holes in the bearing plate into the joists and
blocking below. The upper end of the panel (not visible) is
screwed to the header above.
The epoxy set a few hours after we pumped it in place, but it
needed 24 hours to fully cure before we could apply pressure to
the bolts. A couple of days later, we placed washers and
11/4-inch nuts on the bolts and tightened them against the
bottom of the panels. After making the mistake of thinking we
could find a 11/4-inch deep-well socket at an auto-parts store,
we ended up having to go back to the shear-panel supplier to
Once we had tightened the bolts, finishing the wall was simply
a matter of studding in around the panels and replacing any
plywood missing from the kitchen side (Figure 10). With the
drywall on, it looked like any other wall in the house (Figure
11) — when in fact it will be one of the main structural
elements holding up the building if an earthquake occurs.
Figure 10. The crew
completed the structural work by studding in the panels (top)
and replacing the missing plywood shear sheathing on the
kitchen side of the wall (bottom).
Opening up the shear wall
modernized the floor plan and made the kitchen feel brighter
and more spacious.
Rick McCamydesigns and manages
residential remodels in Walnut Creek, Calif.