Current through Register Vol. 24-18, September 15, 2024
(1)
Girders.
(a) Girders supporting floor joists must be a
minimum four-by-six Hem-Fir #2, spaced not more than eight feet on center, and
placed at least twelve inches above ground.
(b) Girders must be continuous, or must be
spliced over supports. When a girder is spliced over a support, a positive tie
to the support must be provided.
(c) Each end of each girder member must have
a minimum three inch of bearing on treated wood plates or treated wood
posts.
(2)
Floor
joists.
(a) Floor joists must be a
minimum two-by-six spaced sixteen inches on center or two-by-eight spaced
twenty-four inches on center, Hem-Fir #2 or better, spanning not more than
eight feet between supports, and placed at least eighteen inches above
ground.
(b) Floor joists must be
continuous or spliced only over a support with a minimum three-inch
lap.
(c) The end of each joist must
have not less than three inch bearing on treated wood plate.
(d) Notches on the ends of joists cannot not
exceed one fourth the joist depth. Holes bored in joists cannot be within two
inches of the top or bottom of the joist, and the diameter of any such hole
cannot exceed one-third the depth of the joist. Notches in the top or bottom of
joists cannot exceed one-sixth the depth and cannot be located in the middle
third of the span.
(e) Floor joists
must have solid blocking at the ends and at each support. Solid blocking cannot
be less than two inches nominal in thickness and the full depth of the
joist.
(3)
Interior bearing. Interior bearing footings (pads) must be of
plain concrete at least sixteen inches by sixteen inches by eight inches thick
placed on firm undisturbed soil.
(4)
Ventilation. Under floor
areas (crawl spaces) must be ventilated by one-fourth inch screened openings of
not less than one square foot of opening for each one hundred fifty square feet
of under-floor area.
(5)
Supporting interior bearing partitions. Interior bearing
partitions perpendicular to floor joists must not be offset from support
girders more than the joist depth. Interior bearing partitions parallel to the
floor joists must be supported by a doubled floor joist located directly under
the interior bearing partition.
(6)
Subflooring. Subflooring must be structural wood panels (plywood
or OSB), particleboard subfloor or combination subfloor-underlayment, or solid
wood.
(a) Structural wood panels will be
tongue-and-groove installed perpendicular to the floor joists with end joints
occurring over floor joists. The minimum thickness must be five-eighth inches
(eleven-sixteenths inches) over floor joists spaced sixteen inches on center
and three-fourths inches (twenty-five thirty-seconds inches) over floor joists
spaced twenty-four inches on center. Structural wood panels must be grade
stamped for use and span. Secure structural wood panels to the floor joist
system by use of either nails or glue and nails combination. In both systems,
nails must be 8d common or deformed shank, spaced six inches on center at the
edges and twelve inches on center at intermediate supports.
(b) Particleboard subfloor or combination
subfloor-underlayment must be installed perpendicular to the floor joists. The
minimum thickness must be five-eighths inches over floor joists spaced sixteen
inches on center and three-fourths inches over floor joists spaced twenty-four
inches on center. Particleboard must be grade stamped for use and span. Secure
particleboard to the floor joist system by use of either nails or glue and
nails combination. In both systems, nails must be 8d common or deformed shank,
spaced six inches on center at the support edges and twelve inches on center at
intermediate supports.
(c) Solid
wood must be a minimum size of one-inch by six-inch nominal tongue-and-groove
wood strip flooring applied perpendicular or diagonally to the floor joists.
Secure solid wood flooring to the floor joist system by use of either nails or
glue and nails combination as follows for:
(i) Wood strip flooring six inches or less
must be nailed to each floor joist by "2-8d" common or box nails; or
(ii) Wood strip flooring greater than six
inches must be nailed to each floor joist by "3-8d" common or box
nails.
Statutory Authority: RCW 70.114A.081. 99-03-065, §
246-359-220, filed 1/18/99, effective
2/18/99.
