BEFORE THE ARCHITECT
– CUSTOM HOME DESIGNING BACKGROUND
– HOUSE DESIGN ARTICLES
SHEARWALL DESIGN AND SHEARWALL CONSTRUCTION
Before The Architect Copyright 2009
YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION
You've heard of the
walking wounded? Sure, everybody has. Well, I've met their close relatives -
the walking witless. Who are the walking witless? Alice, so glad you asked.
Take this fellow,
please, who a) is generations deep in builders with dad and bro still hard at
it; b) works as a real estate broker; c) enters stage left with a foregone
conclusion on what working with us will cost; d) reckons his bro could do up
this middling addition with a few words of encouragement; e) grinds through 6 -
count them, 6 - draws of a floor plan; f) reckons in spite of that track record
that he doesn't need more than floor and roof framing plans to get it all going
and gone through; g) figures he'll just waive his arms to clue in bro on how the
roofline will work to chop off the bucks out of pocket when he's certain he's
spent enough wherever that's gotten him to the moment he decided that he has
spent enough; h) exits stage right acting as though he's been screwed.
Well, your Honor, he's
right. We're guilty, as charged. This victim's been screwed out of his
egocentric fantasy. That is, unless bro could have spared the time and our
client the cash to build up and tear down five additions before the guys got it
right on the sixth shot. And unless bro's electrician and plumbing subs are
already on pensions. And unless they could get the rooflines just right adding
on to a pristine style for the existing. And unless the local authorities
having jurisdiction will pass a two-story, 2000 square feet of addition without elevations
and a wad of other plans. And unless they're keen on new acquaintances – you
know – debt collection agents, credit reporting bureaus, and lawyers.
Now that's
entertainment. Alice, that's the walking witless. Before The
Architect
INTRODUCTION
 | Shear wall sheathing shall be
 | Not less than 5/8 linear inch, Structural 1
plywood |
| Applied in a vertical orientation only |
| Lapped over sill and top plates, sharing double
top plates in multilevel-overgrade designs
|
|
| Shear wall shall be fastened
| At joints to other sheathing |
| With galvanized wood screws, not nails |
| Driven only perpendicular (i.e., only straight) to
a shear wall plane |
| Not overdriven |
| Only after approval of fastener materials and
methods by engineer, inspector, and contractor |
| For inspection before wrapping the house |
| On not greater than 4 linear inch centers |
| At not less than ½ linear inch in from sheathing
perimeters |
| Without application of construction adhesive at
joints with members
|
|
| Shearwall fastening shall be off eave blocking to roof
frame and top plate, the latter with not less than 3-10d common galvanized
nails per block
| Which eave blocking shall be full depth and |
| Which eave blocking may be bored to let passive
airflow from soffit to ridge or gable vent |
| Which eave blocking shall baffle to block wind
from insulation while still assuring not less than 2 linear inch air gap
to roof deck bottom of face
|
|
| Shearwall fastening of an anchor bolt
| Shall not be double-dutied as a hold-down bolt
|
| Shall be less than 5/8 linear inch in diameter
|
|
| Shearwall fastening of sole plate or mudsill
| Shall be not less than 12 linear inches on center
for bottom, of sole plate, or mudsill |
| Shall be spaced at half field spacing when applied
to walls shear wall- sheathed on both faces |
| Shall be fastened each with a square washer 3
linear inches on a side and not less than 3/16 linear inch thickness |
| Shall penetrate its sill
 | Through a hole not larger than 1/16 linear
inch larger than the bolt diameter, failing which |
| The hole shall be fully filled with a
nonshrink grout or epoxy or epoxy-grout by Laticrete International,
Inc. et al. |
|
| Shall be, with its washer and nut
| Set flush to sill top of face and not recessed
|
| Tightened at the last possible moment finger
tight plus a half-turn |
|
| Shall be as an in-line grouping reinforced with a
single, continuous deformed #5 rebar set a J-bolt curve
|
|
| Shearwall fastening of a tie-down
| Shall be at each end of each wall section
| Applied to a post interior if possible |
| Fastened to a post with self-tapping screws |
| Concentric in application to a post
|
|
|
| Fastening of a shear wall panel
| Shall be applied on the interior directly to
structure and thereafter finished with gypsum wallboard – screwed in
shear wall plywood fastening patterns |
| Shall, as a group and without regard as to whether
its site is interior or exterior, extend at gable end fully from sill to
top plates continuously and without interruption or gaps (except, of
course, for stand 1/8 linear inch spacing between ply sheets) |
| Shall be addressed as a load to be born by
subordinate structure |
| Shall be at each and every one of its intra-bay
joints blocked fully and firmly with x4 whole or built-up lumber
|
|
| Load paths
| Shall be of materials continuously solid and
sufficient throughout to prevent crushing, notably (and preferably)
up-sizing posts, and blocking below post- and stud-loaded sills, i.e.,
crush blocks |
| Shall be of metal connectors, straps, hangers,
etc. fastened only with a full complement of nails or screws specified
by the manufacturer or engineer of record |
| Shall be of connections of members shall be to
full members without exception
|
|
| Shear wall shall be braced
| With not less than full-depth, solid blocking |
| With not less than x4 material, whole or built-up
| On center to blocking at joints and |
| On not greater than 6 linear feet centers |
| Plus inside of and tight to top and bottom
plates |
|
| Not with flat straps for compression |
| Possibly with block-U, structural steel channel |
| Possibly – with space to be taken up – with
members sistered at 90-degrees to studs' narrow faces
|
|
| Shear wall shall be framed
| With not less than x4 nominal width, i.e., narrow
face, at all joints to sheets and otherwise at all perimeters of sheets |
| With not less than x6 linear inch nominal depth
members overall |
| Maybe of engineered lumber |
| With metal hangers and not jack studs to affix a
beam, including a header |
| Where jack studs are changed-out for king studs |
| With lumber
| Identified by the grade mark of a lumber
grading or inspection bureau or agency approved by the American
Lumber Standards Committee (a/k/a ALSC) |
| Group 2 or 3 |
| Not less than #2 Grade |
| In decreasing order of preference of specie:
Douglas Hemlock Fir-Larch; Southern Yellow Pine; Spruce-Pine-Fir,
the latter for engineered applications only and then Only as last
resort |
| Naturally continuous for a given member |
| Fully dimensioned |
| With members on application not less than 2
linear inches in nominal thickness in the field |
| With members on application not less than 4
linear inches – built-up or whole – in nominal thickness |
| With members at sheathing sheet joints to
other sheets; in any case, at perimeters |
| Containing not more than 12% moisture content
on delivery to the jobsite, on application, and on closing |
| Except preservative-treated wood products
which shall contain not more than 19% moisture content on delivery
to the jobsite, on application, and on closing |
| Determined to have been stored dry before
being delivered to a site |
| Delivered to a site on other than a rainy day
and |
| Stored on a site sheltered from natural
elements |
| If graded, then not ripped to structural
application |
| If engineered, may be ripped if appropriate
adjustments are made to performance metrics given the member's
post-rip dimensions |
| As rim board or end or head joist of solid,
sawn lumber or engineered lumber
|
|
|
| Shear wall shall be sheathed
| Separated with framing clips |
| Fastened directly to a member |
| Fastened firmly and without bending and gapping to
a member |
| Fastened with the full complement of nails or
screws prescribed by the manufacturer
| Applied in lieu of toed nails in fastening
blocks and end and head joists, or rim boards, to subordinate
structure |
|
| At plates, nails shall be applied one size above
that specified for nonshear wall application
|
|
| A shear wall sole plate or mudsill above concrete
| Shall have a moisture impermeable membrane, e.g.,
galvanized steel, EPDM, peel-and-stick, etc., shall be applied
continuous between sill atop foundation and the foundation top of face
|
|
| A concrete foundation below a shear wall
| Shall be tied on the vertical by not less than
Grade 50-#5 deformed rebar
| Which rebar hook shall be 3 linear inches up
from the footing bottom of face |
| Which rebar shall be set on not greater than
16 linear feet centers in the field |
| Which rebar shall be set not greater than 1
linear foot from a terminus or change in footing direction (both
sides) |
| Which rebar shall number not less than two in
any foundation segment |
| Which rebar shall extend into a foundation
wall not less than 40 bar diameters, noting that if this last
prescriptive presents the reinforcement above the wall top of face,
then lower the footing depth sufficiently to let 3/4 linear inch
plus maximum aggregate size cover to wall top of face
|
|
|
| Sill stock shall be labeled "KDAT" (a/k/a kiln dried
after treatment)
|
| An opening in a shear wall shall be reinforced
| With not less than full-depth, solid blocking in
line on horizontal with header (flush to header bottom of face) and top
sill plate from opening to perimeter stud of the shear wall in both
directions
| Which blocking shall be below a continuous
steel strap for tension not compression from across the wall from
perimeter to perimeter |
|
| With continuous steel strap for tension not
compression on the vertical in-line with the innermost jack stud
extending from both top plates down to the sill plate(s)
|
|
| Sheathing shall be fastened to the king studs either
side (please note that metal hangers shall be in lieu of jack studs) with
not less than 10d box nails on not greater than 4 linear inches center
|
| In stepped foundations, cripple shear walls shall have
connections concentrated on highest segment, notwithstanding alternative
engineering
|
| A strap
| Shall be straight and true and not kinked, bowed,
twisted, or bent |
| Shall be applied for tension and not compression
|
|
| A shear wall post if built-up
| Shall be stagger-nailed with 16d common galvanized
at 6 linear inches on center |
| Shall be arranged in-line vertically wherever
possible |
| Shall be not less in dimension than the post above
it, notably including crawlspace cripple walls
|
|
| Assure that metal fasteners in contact with
preservative-treated wood are appropriately qualified for durability
|
| Suggested PROHIBITEDS in shearwall construction, there
| Shall be no let-in bracing |
| Shall be no Oriented Strand Board, or OSB, or
other particled board applied as sheathing |
| Shall be no sill anchor or other substitute for an
anchor bolt |
| Shall be no nails with heads other than fully
rounded, e.g., Sheather Plus by Stanley-Bostitch or similar |
| Shall be no nails other than common galvanized or
their equivalent shank diameter. |
| Shall be no framing member that is
| Standard or utility grade lumber |
| In quality less than #2 |
| Lumber finger-jointed |
| Lumber end-jointed |
| Members scabbed |
| Members butted |
| Members spliced |
| Shall be no slots cut in a wall |
| Shall be no doubled panels on a given panel
face |
|
| Shall be of no fasteners
| Other than steel |
| Of type including screws of any sort |
|
| Shall be no plumbing conduit within a wall |
Comment: In view of other prohibitions of wall mass
amendments and other insults, this means that conduit of any sort shall not
be permitted in shear walls. Note well that such prohibition might not
extend to a centerlined bore for a water supply pipe or a small number of
electrical cables
| Shall be no strap tie-downs |
| Shall be no keyed footing or cold-joint between
foundation foot and placed wall, i.e., shall be footing and wall shall
be monolithic |
| Shall be no prefab shear walls or bracing panels
without the express advice and consent of the engineer of record,
owner(s), and both general and supporting sub-contractor
|
|
| Tie-down rod shall lean not greater than 1 linear inch
on the horizontal for each foot of rod length; otherwise, replace the
tie-down
|
| Height-to-length ratios shall be respected, especially
in re plate amendments of any sort, e.g., cable or water supply intrusion
(again, even these minor insults should be and almost always can be avoided
in shear walls), at a maximum of 3:1 without engineering an abundance of
caution |
