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Before The Architect
FRAMING A HOUSE WITH JOISTS
AS FLOOR STRUCTURE AND CEILING STRUCTURE
INTRODUCTION
This article is
about framing a house with floor joists and ceiling joists. Way more than you'll likely find anywhere
else.
Home framing
"joists" can be end joists or joist ends, common or field joists, head
joists or joist heads, ribbons, bands, doubled joists, and similar.
Joists can be
floor structure and ceiling structure.
ABOUT JOISTS HOME
FRAMING STANDARDS
Joists shall be
spaced at not greater than 16 linear inches on center
Comment: Not greater
than 16 linear inches… period. Doesn’t matter whether they’re hand-framed or
trussed, ceiling structure or floor structure. Period. Not negotiable.
Joists
Shall bear
in-line to wall studs and posts
Supported by
hangers shall be physically, firmly engaged by such hangers to the full
depth of the hung joists
Shall bear on
engineered lumber which in turn bears on hangers, walls, and posts
Joists bearing
directly on load-bearing walls
Shall have not
less than 1 1/2 linear inches bearing on wood
Shall have or
not less than 3 linear inches bearing on masonry
Failing which
joists shall be fastened at their butts with appropriate joist hangers
by Simpson Strong-Tie or equivalent
Joists exposed
directly to masonry shall be preservative-treated, unless
preservative-treated spacers will suffice at, for example, joist ends only
bearing on masonry
Joists exposed to
weather from any direction or located within 18 linear inches of exposed
earth shall be preservative-treated
In a joist
Notches and
bored holes shall not be applied in the middle 1/3 by length (not width)
A bored
hole shall not be within 2 linear inches of the top or bottom or end
of the framing member and
The
diameter of a hole shall not exceed 1/3 the member’s true depth (not
length)
A notch and a
bore shall not be in the same joist
A field notch
in the top or bottom
Shall not
be greater in depth than 1/6 the framing member’s true depth (not
length) and
Shall not
be greater in length than 3 times the member’s true depth (not
length)
An end notch
Shall be
not greater in depth than ¼ the member’s true depth
Shall be
not greater in length than the top plate top of face on which it
rests
A notch or a
bore may be applied only in a singled joist
A taper
Shall be only
to a joist top of face
Shall be not
greater in length than 3 times the member’s true depth
Shall be not
greater in depth than ½ the member’s true depth
Taper,
Bore, and Notch Study, Section in Elevation
Key to abbreviations: D=Depth; NTS=Not To Scale
Comment: To make the
point that what you’ve just read isn’t as straightforward as you might have
thought, the illustration above is offered.
Comment: THIS CUSTOM
HOME DESIGNER is amazed and amazed again and again when holes and notches are
right where they’re not supposed to be. Usual culprits from lesser to greater:
HVAC contractors, electrical contractors, plumbing contractors.
Load-bearing walls
parallel to floor joists (and beams)
Shall be
continuously and directly supported by a subordinate bearing Structure
as in double joists, beams, girders, or other load-bearing walls, or
Failing that,
shall be subject to offset not greater than the true depth of the floor
joist centerline to centerline with the subordinate bearing structure
and
The subordinate
joist bay of which
Shall have
solid, full-depth blocking
At not less
than midspan and
At not
greater than 16 linear inches on center and
The joist
that shares the bearing shall be doubled in new structure, or
The joist
that shares the bearing shall be otherwise reinforced in renewed
structure
Load-bearing walls
shall not be offset from supporting beams, girders, or other load-bearing
walls by more than the true depth of the floor joists and in new
construction the outside joist shall be doubled
If walls are
parallel to a supporting floor joist, then the floor joist supporting the
wall shall be doubled
Floor joists
Supporting
floor-loaded
Bathroom
fixtures
Masonry
hearths
Kitchen
islands
Kitchen
appliances
Water tanks
Water
heaters
Extraordinarily large pieces of furniture the planned placement of
which is known beforehand (e.g., Bavarian sideboard, grand piano, a
humongous fish tank, etc.)
And similar
Shall be
Not less
than doubled if hand-framed and
Not less
than dropped one notch in span if truss-framed, e.g., from 24 linear
inches on-center to 16 linear inches on center
Comment: The only thing
worse than a plumber unattended when running DWV pipes is a bouncy joist.
Joists shall have
full-depth, solid blocking evenly
At
Not less
than midspans for each joist and
Not greater
than 8 linear feet on center for each joist
Between
members supported, e.g., over purlins and plates
Joist ends
not headed or set with a metal connector or hanger
A beam shall be
neither notched nor bored
A girder shall be
neither notched nor bored
A header shall be
neither notched nor bored
Ledger strips
Shall not be
less than 2 linear inches x 2 linear inches nominal and
Shall be
applied only to assist in hanging structural framing members and
Shall not be
applied as a permanent structure, unless
Not less
than 2 linear inches x 4 linear inches and
Fully
flushed to structure on wider dimension and
Plated as
Doubled Joists (Face-nailed)
Metal hangers
Shall be
fastened
With not
less than 10d nails when more than 1 member is hung and
With not
less than 16d nails when more than 1 member hung (except that
Strong-Tie SDS screws may be applied with Strong-Tie connectors in
accord with manufacturer’s specifications, or where ductile strength
is a significant structural issue, e.g., seismic applications)
Failing which,
nails applied shall be in diameter not less than a 10d common galvanized
nail
Nails applied
shall not be less than 1 1/2 linear inches in length overall
For
single-member hangers, allowable spans shall be reduced by not less than
77%
For
double-member hangers, allowable spans shall be reduced by not less than
64%
Shall be
applied only to full depth of supported member
Framing below HVAC
air handlers, furnaces, water heaters, water tanks, and similar
Shall not be
less than 2 linear inches x 8 linear inches
Shall be on not
greater than 16 linear inches centers and
Shall be
sheathed
With not
less than 3/4 linear inch plywood
Over not
less than the entire burdened surface area
Plus not
less in all directions than 32 linear inches or 2 joists
Whichever
is greater
Joists over crawl
spaces shall not be less than 18 linear inches over grade
Beams over crawl
spaces shall not be less than 12 linear inches over grade
Ceiling joists
shall be spaced at equal on-centers to the rafters to which the joists shall
be fastened
Joist spacing below
walls and below plumbing fixtures shall be adjusted to let drainpipe at not
less than 6 linear inches diameter clearance on centerpoints
Comment: Therefore, for
parallel bearing walls set double joists apart approximately 1 ¼ linear inches
outside each side of a partition bottom plate.
Joist spacing below
walls –
Shall be
adjusted to let water supply pipe at not less than 1 ½ linear inches
diameter on centerpoints; therefore
For parallel
bearing walls, set double joist apart approximately 1 ½ linear inches
each side of a partition bottom plate centerline
A Pressel-Ballard
Brace (named in part for Bob Ballard, the engineer who dreamed it up with
this home designer)
May be applied
to strengthen an existing joist
When doubling
and other means are not viable for reasons of
Access
Physical
movement
Gas or
water plumbing continuity
Electrical
cable continuity, etc. and
When 1 ½ linear
inches loss of clearance from the bottom face of the existing is neither
impeded nor an impediment
May be applied
to either
The bottom
of a joist, e.g., a floor joist
The top of
a joist, e.g., a ceiling joist with unfinished attic exposure
Where the
Pressel-Ballard Brace consists of
Full and
unamended framing members of not less than #2 grade
As wide as
feasible
Plated tight to
each vertical face of existing and
The plated
members resting as deeply as possible on existing plates or are metal
hangered and
A third framing
member at 2 linear inches x 6 linear inches nominal (for a joist and 2
sisters’ width approximately) is plated on the horizontal bottom of face
to each of the 3 members — the joist and the sisters
Pressel-Ballard
Brace, Section in Elevation
Floor joists below
natural or ceramic tile shall be applied at the stiffer of
Application at
not greater than 12 linear inches on center and with solid, full-depth
blocking at not greater than 12 linear inches on center or
0therwise to
achieve a deflection limit for ceramic tile of not less than L/600
(personally assigned deflection limit)
0therwise to
achieve a deflection limit for natural stone not less than L/720 with
members space not greater than 12 linear inches on center
Comment: “Tight joist
spacing is great for tile as it minimizes sheathing curvature due to lower
bending moments in sheathing." Frank Woeste, P.E., Ph.D., Professor of Wood
Construction & Engineering, Virginia Tech.
Strongbacks shall
be applied to metal plate-connected floor trusses
As close as
possible to midpoints and
Perpendicularly
to truss orientation and
Of 2 linear
inches x 4 linear inches or x 6 linear inches lumber set vertically
faced to the bottom chord, and fastened with not less than 4 nails not
less than 10d to a vertical web or
Fastened to
both bottom and top chords
With a
scrap scabbed to span both chords on the vertical
Which scrap
shall be the same dimension as the Strongback and
The nails shall
be in size and total equal to the nails that fastened the strongback to
the scabbed scrap
Load-bearing joists
(and plates) shall be fully supported by structure below their entirety,
notably including full support between foundation and sills and soles
Joists, on their
to-be finished faces
Shall not be
greater than 1/16 linear inch difference between any three on their
shared plane
Shall be
shimmed level for not greater than 1/16 linear inch difference between
any three on their shared plane
I-joists
Comment: Know well that
THIS CUSTOM HOME DESIGNER ‘s not big on so-called wood I-joists, you know, two
little strips of pine stuck on either edge of particle board, looks like a
capital ‘I’ in section. Why’s that? Bunch of reasons, most of which have to do
with how they’re mishandled and only one about the material itself. Plus,
there’s a substantially superior alternative almost everywhere you go these days
(except maybe still the East end of Washington State and Shasta County, CA) –
wood, metal plate-connected, open web trusses.
Why this custom
home designer does not prefer wood I-joists, by this custom home designer
Practically
begs trades to cut ‘em up willy-nilly for laying in conduit
Air
Water
supply
Water waste
Gas
Electrical
Can get in the
way as much as sawn lumber in maneuvering mechanical accoutrement in
tight spaces such as a low crawl, that is, relative to open web floor
joists
Similarly, can
raise blood pressure in finishing a basement
Reminiscent of
an early advertisement for nylon stockings that assured these niceties
wouldn’t “rip, run, tear, small, or bag at the knees," I-joists are so
user-friendly – they can roll, warp, twist, and otherwise distort pretty
easy before installation and, if conditions are just right, then after
installation, too
Get particle
board good and wet, see the strength come out of it and stay out of it
Guys who ought
to know better count on less withdrawal strength relative to engineered
wood rim boards to hang elements, such as a deck, quickly and simply
If you must
apply I-joists, then do it this way:
Store ‘em
continuously supported and out of the elements pre-application
Follow
manufacturer’s specifications scrupulously for boring and notching
and trimming
Make sure
the hangers fit the entire end of the member, i.e., both flanges
fully and tightly.
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Before The
Architect, please consider spending a few moments looking over the
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Map, in order to get a feel for the website design.
Before The Architect E-mail:
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