Shearwalls for Coastal Homes, continued
Case Study
My current project illustrates how I incorporate these
structural solutions into my design concept from the outset
(see "A House by the Water," below). The main house is based on
a traditional colonial rectangular shape but with several
polygon bays. The bays gather in sunlight and air but are also
stronger elements than flat faces that have to be
reinforced.
For framing efficiency, I used full-length 40-foot wood
I-joists for the first floor, running them from end to end of
the house. They are supported on the two end walls and on three
framed walls built on their own footings in the basement.
Two of the cross-basement walls also act as shearwalls,
anchoring the first-floor diaphragm. Stacked directly above
them is a pair of first-story shearwalls, which carry their
share of the second floor's live and dead loads and also serve
to handle any lateral load carried into the house by the
second-floor diaphragm. Above those two walls I set a third
pair, which support the second-floor ceiling (the attic floor)
and lock the floor and ceiling diaphragms for that story into
the whole-house assembly.
Case Study: A House by the
Water
The author designed this oceanfront home with
code shearwall requirements uppermost in his mind
from the concept stage. Working with an engineer,
he stacked two primary first-story and second-story
shear panels directly above basement-level
shearwalls (section, below). In this way, he was
able to accommodate most of the wind loads from the
long axis of the house without cramping the
generous space desired in ocean-facing rooms (floor
plan, below). The unbroken expanse of the
north-facing end wall also contributes (top photo).
This wall was left windowless intentionally because
it faces the neighboring house on the narrow lot.
While the east-facing wall has many windows, the
polygonal jogs provide lateral strength through
geometry — the same way right-angle jogs in a
long foundation wall do.
Proper shear panel nailing and hold-down placement
are critical, so the engineer prepares a separate
plan sheet and fastener schedule for this purpose.
The schedule lists the hold-down spec and plywood
nail size and spacing for each shear panel location
(below). Shear Panel & Hold-Down
Schedule
All plywood panel locations (shown shaded above)
are to be fastened to studs using 8d nails spaced
at 6" on-center at all plywood edges and at 12"
o.c. at all intermediate members except for the
specially designated shear panel types indicated
below.
Mark | Force | Height | Length | Shear | Hold-Down | Plywood
Attachment | Hold-Down
Connector | SP1 | 7680 | | 20 | 384 | 3072 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD5A into (2) studs | SP2 | 12408 | 10 | 24 | 517 | 5170 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD8A into (2) studs | SP3 | 9040 | | 16 | 565 | 5085 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD8A into (2) studs | SP4 | 4032 | | | 576 | 5184 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD8A into (2) studs | SP5 | 3552 | | | 395 | 3552 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD5A into (2) studs | SP6 | 13760 | | 20 | 688 | 6192 | Glued with 8d nails at 4" o.c. at
edges, 12" o.c. intermediate | Simpson HD8A into (2) studs | SP7 | 8256 | | 21 | 393 | 3538 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD5A into (2) studs | SP8 | 6144 | | 12 | 512 | 4096 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD6A into (2) studs | SP9 | 6885 | | 13 | 530 | 4767 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD8A into (2) studs | SP10 | 3090 | | | 515 | 4635 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD8A into (2) studs | SP11 | 1650 | | | 275 | 2475 | 8d nails at 6" o.c. at edges, 12" o.c.
intermediate | Simpson HD5A into (2) studs | SP12 | 13760 | | 24 | 573 | 4587 | 8d nails at 4" o.c. at edges, 12" o.c.
intermediate | Simpson HD8A into (2) studs |
• All designated shear panels are to have
solid blocking installed between studs along
plywood edges.
• All Simpson hold-down connectors at the
second-floor level are to be fastened through to
the shear panel below.
• All Simpson hold-down connectors at the
first-floor level are to be fastened into the
foundation wall or supporting beam.
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