Section 27-622. Empirical provisions in lieu of design

The provisions of
  this section may be used in lieu of structural analysis only  for  those
  buildings   in  occupancy  group  J-3  where  the  specific  occupancies
  correspond to a live load requirement of forty  psf,  or  less,  and  to
  constructions  wherein  the  supporting  framing  consists  of multiple,
  closely spaced members, such  as  joists,  studs,  platform  or  balloon
  frames.  All  wood  structural  members in other classes of construction
  shall be proportioned on the basis of  the  analysis  of  stresses.  All
  requirements established in this section may be reduced when an analysis
  of  stresses,  executed  in  accordance with reference standard RS 10-8,
  indicates such reduction is feasible. Sizes of wood  members  stated  in
  this section are nominal sizes.
    (a) Stud walls and partitions.
    (1)  Studs  shall  be  of  equivalent or better grade than the minimum
  grades for the various species as established in reference  standard  RS
  10-13.
    (2)  Corner  posts  shall  be  3-stud members or members of equivalent
  strength.
    (3) Load bearing studs shall be set  with  the  larger  cross  section
  dimension  perpendicular  to  the  wall  or partition. Studs in exterior
  walls of one story buildings of construction class II-D and  II-E  shall
  be  at  least  two  inches  by three inches spaced not more than sixteen
  inches on center, or where studs are two inches by four  inches,  spaced
  not  more  than twenty-four inches on center. Studs for other classes of
  construction shall be at least two inches by four inches spaced not more
  than sixteen inches on center.
    (4) Stud walls resting on concrete or  masonry  shall  have  sills  at
  least  two  inches  in  nominal  thickness.  Where  such  sills  bear on
  concrete, they shall  be  fastened  with  minimum  one-half  inch  bolts
  embedded  at  least  six inches. Each sill piece shall have at least two
  anchor bolts, with one bolt located at least one inch from each  end  of
  the plate, and with intermediate spacing not more than eight feet. Where
  such  sills  bear  on masonry, they shall be anchored in accordance with
  the applicable provisions of reference standard RS 10-1.
    (5) Stud partitions that rest directly over each  other  and  are  not
  parallel to floor joists or beams may extend down between the joists and
  rest  on the top plate of the partition, partition girder, or foundation
  below, or may be constructed on sill plates running on top of the  beams
  or joists.
    (6)  All  load  bearing  stud  partitions shall be supported on walls,
  other partitions, double joists or beams, solid bridging, or on beams at
  least as wide as the studs. Joists supporting a  partition  parallel  to
  the  joists wherein the joists are spaced apart to permit the passage of
  piping or duct work shall be provided with solid blocking  at  intervals
  of not more than sixteen inches.
    (7)  Load  bearing  partitions  perpendicular  to  joists shall not be
  offset from supporting girders, walls or partitions  by  more  than  the
  depth  of  the joists unless the joists are proportioned on the basis of
  analysis of stress.
    (8) In interior walls and in bearing partitions, double studs shall be
  provided at the sides of openings that are greater than three  feet  six
  inches  up  to  six feet in width, and triple-studs shall be provided at
  the sides of openings of greater width.
    (9) Headers shall be provided over each opening in exterior walls  and
  bearing  partitions.  Where the opening does not exceed three feet, each
  end of the header shall be supported on a stud or framing anchor.  Where
  the  opening exceeds three feet in width each end of the header shall be

  supported on one stud and where the opening exceeds six  feet  each  end
  shall be supported on two studs.
    (10)  All  studs  in exterior walls and in bearing partitions shall be
  capped with double  top  plates  installed  to  provide  overlapping  at
  corners  and  at  intersections with other walls and bearing partitions.
  End joists in double top plates shall be  offset  at  least  twenty-four
  inches.  In  lieu  of  double top plates, a continuous header of similar
  dimensions may be used. For platform  frame  construction,  studs  shall
  rest on a single bottom plate.
    (b)  Bracing of exterior walls. Exterior stud walls shall be braced by
  one inch by four inch continuous diagonal strips let into  the  face  of
  the  studs  and  into  the  top  and bottom plates at each corner of the
  building. Bracing may also be provided by one of the following means:
    (1) Wood board  sheathing  of  one  inch  nominal  thickness,  applied
  diagonally.
    (2)  For  one and two-story dwellings, plywood sheathing at least four
  feet by eight feet (except where cut to  fit  around  openings  and  for
  similar purposes) and at least five-sixteenths of an inch thick on studs
  spaced  sixteen  inches or less on centers and at least three-eighths of
  an inch thick on studs spaced more than sixteen inches but not exceeding
  twenty-four inches on centers.
    (3) For one story dwellings and for  the  upper  story  of  two  story
  dwellings,  fiberboard  sheathing  applied vertically in panels at least
  four feet by eight feet (except where cut to fit around openings and for
  similar purposes). Fiberboard sheathing shall be at least one-half  inch
  thick  and  shall  conform  to  the  provisions of reference standard RS
  10-27.
    (4) For one story dwellings and for  the  upper  story  of  two  story
  dwellings,  gypsum  board  sheathing  applied  horizontally in panels at
  least two feet by eight feet (except where cut to  fit  around  openings
  and for similar purposes). Gypsum boards shall be at least one-half inch
  thick  and  shall  conform  to  the  provisions of reference standard RS
  10-19.
    (c) Floor and roof framing.
    (1) SPAN TABLES. Joists and rafters may be  used  in  accordance  with
  reference standard RS 10-13.
    (2)  BRIDGING.  In all floor and roof and roof framing, there shall be
  at least one line of bridging for each eight feet of span. The  bridging
  shall  consist  of  at least one inch by three inch lumber or equivalent
  metal bracing. A line of  bridging  or  solid  blocking  shall  also  be
  required  at supports unless lateral support is provided by nailing to a
  beam, header, or to the studs. Midspan  bridging  is  not  required  for
  floor or roof framing in one- and two-family dwellings where joist depth
  does  not exceed twelve inches. Bridging shall bear securely against and
  be anchored to the members to be braced.
    (3) NOTCHES. Notches in the ends  of  joists  and  rafters  shall  not
  exceed one-fourth the depth unless adequate reinforcement is provided or
  analysis of stresses indicates that larger openings are feasible without
  the  necessity  for reinforcement. Notches in joists or rafters, located
  in the span shall not exceed  one-sixth  the  depth  and  shall  not  be
  located in the middle third of the span. Bored holes shall not be within
  two inches of the top or bottom of the joists or rafter and the diameter
  of  any  such  hole  shall  not  exceed  one-third  the depth. For stair
  stringers, the minimum effective depth of the wood at any notch shall be
  three and one-half inches unless the stringer is continuously  supported
  on a wall or partition.
    (4) SUPPORT.
    a. Floor or roof framing may be supported on stud partitions.

    b.  Tail  beams over twelve feet long and all header and trimmer beams
  over six feet long shall be hung in metal stirrups having anchors, or by
  other methods providing adequate support. Trimmers and headers shall  be
  doubled where the header is four feet or more in length.
    c.  Except where supported on a one inch by four inch ribbon strip and
  nailed to the adjoining stud, the ends of floor  joists  shall  have  at
  least one and one-half inches of bearing on wood or metal, nor less than
  four inches on masonry.
    d.  Joists  framing  from  opposite  sides of and supported on a beam,
  girder, or partition shall be lapped at least four inches and  fastened,
  butted  end-to-end  and  tied by metal straps or dogs, or otherwise tied
  together in a manner providing adequate support.
    e. Joists framing into the side of a wood girder shall be supported by
  framing anchors, on ledger strips at least two inches by two inches,  or
  by equivalent methods.
    f.  Wood joists and rafters bearing on masonry walls shall be anchored
  to such walls in accordance with the applicable provisions of  reference
  standard RS 10-1.
    (5) RAFTERS AND CEILING JOISTS.
    a.  Where  rafters meet to form a ridge, they shall be placed directly
  opposite each other and nailed to a ridge board at least one inch thick,
  and not less than the cut end of the rafters in depth.
    b. Provisions shall be made to resist the thrust from inclined rafters
  by connection of collar beams at  least  one  inch  by  six  inches,  by
  connection to joists, or by equivalent means.
    c.  Where  ceiling  joists are not parallel to rafters, subflooring or
  metal straps attached to the ends of the rafters shall be installed in a
  manner to provide a continuous tie across the building.
    d. Ceiling joists  shall  be  continuous,  or  where  they  meet  over
  interior  partitions,  shall  be securely joined to provide a continuous
  tie across the building.
    e. Valley rafters shall be double members. Hip rafters may  be  single
  members.  Valley  and  hip  rafters shall be two inches deeper than jack
  rafters.
    f. Trussed rafters shall be designed in accordance with the provisions
  of reference standard RS 10-8.
    (6) Built-up members shall be securely spiked or bolted  together  and
  provision   shall  be  made  to  resist  the  horizontal  shear  between
  laminations.
    (d) Nailing schedule. The size and number  of  nails  for  connections
  shall be in accordance with table 10-4.