Stud Wall Design Standards

INTRODUCTION

• Almost everybody’s got ‘em – stud walls. 
  • They’re the bones of almost all houses in the US.  Building them is mostly regarded as commodity work. 
  •  Did you know that the design of wood stud walls can vary widely – to the benefit or bane of owners? 
• Builders will bring their own standards or you can set yours. 
• This article is about setting your own stud wall design standards. 
  • A few of the entries are straight from code, included by force of their occasional failure to be performed. 
  • The rest address quality for safety and durability.
• Please note, dear reader, this monograph does not directly deal with either high-wind resistant or seismic structure, both of which are subjects of engineering latitude.  However, much of the precepts to follow are relevant to the high-stress structures. 

DESIGN STANDARDS FOR STUD WALLS, WOOD 

• Mudsills and sole plates for exterior walls, when in direct contact with masonry, shall be preservative-treated
• Wall stud
  • Spacing shall not exceed 16 linear inches on center
  • Shall be placed with its face perpendicular to wall lines
• Top plates
  • Butt joints – both upper and lower top plates 
    • Shall be supported by not less than 1 stud
    • Set to share both butts equally 

Comment:  That is, neither top plate member’s butts shall be unsupported by a stud – either full or equally shared.

To be clear – since this framing error is very common and can be very serious (AG and The Missus have seen distortion of unsupported butts greater than their depth when a superior wall line is bearing), here’s how not to frame a top plate butt joint – see how it’s completely unsupported by a stud on which both butts should share space atop . . . . . 

Top Plate Butt Joint, Unsupported - Wrong

  

• Shall be overlapped at corners and wall intersections
• Laps shall be staggered at not less than 4 linear feet
• Laps shall be fastened with not less than 18-16d common nails evenly spaced, not less than nine on each side of a lap
• Shall be continuous over cripple studs
• Butt joints in bottom plates
  • Shall be double-fastened within 3 linear inches of each butt
    • With not less than 2-10d common nails in each butt
• In wall studs
  • Notch depth shall be limited to 20% of the actual (not nominal) stud depth whether load-bearing or nonload-bearing
• Bored holes in nonload-bearing studs
  • Shall be limited to 40% of actual (not nominal) stud depth and
  • Shall be limited to 60% of the actual (not nominal) double- stud depth and
  • Shall be on-center
• Bored holes in load-bearing studs
  • Shall be limited 20% of the actual (not nominal) stud depth and
  • Shall be limited to 60% of the actual (not nominal) double-stud depth and
  • Shall be on-center
• A notch or a bore shall not be made within 3 linear inches of a butt
• A notch or a bore shall not be made within the middle third of a member as measured in length not width
• A notch and a bore shall not occur in the same stud and
• Only one notch or (not “and") one bore shall occur in the same stud 

Four-Stud Corner, Section in Plan View

 

• Exterior, right-angle corners shall be built of not less than 4 studs, laid out as depicted in Four-Stud Corner, Section in Plan View, of not less than 2x6 members
• In no instance shall there be an uninsulated void in a wood stud wall, notably out-facing but not to the exclusion of in-facing, too 

Comment:  This custom home designer prefers that all corners be built this way, but that’s just him. 

• Stud walls shall be braced
  • With let-in steel strap or wood brace attached to both top plates and the sole plate(s) at angles to the horizontal not less than 45° and not greater than 60° or
  • To studs not less than doubled at angles to the horizontal not less than 45° and not greater than 60°
  • At wall lengths not greater than 25 linear feet
  • Whether a wall is load-bearing or
    • Failing these standards, then solid full-depth blocking shall be applied at midspans for bracing, noting that such blocking may be applied independently for fire-blocking

Comment:  Note that wall bracing rules change dramatically at Seismic Zone 3 and up and can change at least some here and there in Seismic Zone 2A and 2B.

• Window framing
  • Shall have double sill plates, or double bench or double saddle and
  • Shall have supporting cripples, or sill jacks, at opposing butts plus cripples common-spaced
  • Blocking shall be
    • At not less than midspan and
    • On not greater than 8 linear feet centers
    • Solid
    • Full-depth
• For purposes of framing (i.e., not foundation), all walls shall be considered load-bearing unless otherwise noted
• A beam not less than 4 linear feet clearspan shall be supported by not less than 3 linear inches rest on top plate top of face or by joist hanger, plate, or other steel connector
• A tub or shower inset shall be framed to let water supply lines and controls an unobstructed clearance to 6 linear inches either side of the centerline of each interior wall face
• Headers of dimensioned, or sawed lumber
  • Shall be of moisture content not greater than 12%
    • At delivery to site
    • At application and
    • At closing
    • All reasonable steps shall be taken to make it so and keep it so, and
• When not less than 4 linear feet in clearspan or when acting as shearwall
  • Shall be trimmed at each end by double king studs and
  • Shall be supported by double jack studs, or jamb studs, or trimmer studs and
• When less than 4 linear feet in clearspan or when acting as shearwall
  • Shall be strapped to header studs with not less than 2 Simpson LSTA straps on each end
  • Shall be trimmed at each end by not less than a single king stud and
  • Supported by not less than a single jack stud, or jamb stud, or trimmer stud and
  • Shall be strapped to header studs with not less than 1 Simpson LSTA strap at each end
• When acting as shearwall, or braced wall, in corners, shall be run tight to the corner structure

Jack Stud at Window Sill Plate, Severed - Wrong

 

• Shall not be severed or otherwise amended throughout as, e.g., by butting to a window sill plate top of face 

Comment: The jack studs’ continuity in application to window framing should be easier to grasp than the author’s experienced, he thinks.   So here’s a pic of doing it wrong – see the split jack at the single (not double) sill plate in the illustration Jack Stud at Window Sill Plate, Severed - Wrong. 

• In interior bearing applications
  • A flitch shall be plated between the header members for structure in a x 4 linear inches wall or multiples, and 2 flitches in a x 6 linear inches wall
    • Therewith taking up wall stud depth entirely and
  • The header shall be sized to code plus one size up
    • Except that if code requires x 12 linear inches members
      • Then that header shall be specified with engineered lumber
• In exterior applications
  • Either a foam insulation or
  • Air space shall be set to the interior face
  • In bearing application
    • Shall be sized to code plus one size up
      • Except that if code requires x 12 linear inches member
        • Then that header shall be specified with engineered lumber
• In applications of significant wall amendment by large or numerous door or window features
  • Then each header shall be strapped
    • With longest appropriate length of Simpson TS or equivalent
    • From header, across top plates, and onto either ceiling joists or braces to ceiling joists or
    • By solid blocking or bracing
    • In any case at not greater than 24 linear inches on center 

Comment:  This last point is about durability.  In increasingly favored designs of larger and larger windows and, especially, doors, the unbraced walls which these features amend can become unstable….close a door with gusto and the wall shakes….a wind gust rattles the interior around the big window with the swell view. 

• Braced exterior wall on L1 shall be fastened to code, except that
  • Nailing shall be with not less than 16d sinkers
• Anchor bolts 
  • Shall not be less than 2 per braced wall segment and
  • Shall not be greater than 2 linear feet apart on center
  • Shall not be less than 5/8 linear inch in diameter and
  • Not less than 15 diameters embed (about 10 linear inches)
• Nailing patterns
  • Shall be at 4 linear inches on center
    • On both vertical and
    • Horizontal
    • Through sheathing
    • To EACH MEMBER
      • Including header and
      • EACH stud
    • Tight to top plates in a braced wall segment or cripple studs set in common spacing and flush to both jack, or trimmer, or jamb studs
    • Steel-strapped securely fastened to both top plates, header, and not less than 18 linear inches of jamb, or jack, or trimmer stud(s) at each end
• Holdowns shall be
  • At both cornered faces and not just the short face
  • Braced interior walls at L1 and L2 and above shall be
    • Membered and
    • Fastened as in immediately above
      • Except that
        • Let-in braces may be applied in lieu of ply sheathing and
        • Wall board shall be fastened with screws at relaxed patterns
• Braced exterior walls on levels above L1
  • Shall be membered and
  • Fastened as in immediately above
    • Except that
      • Not less than 5/8 linear inch carriage bolts may be applied
      • In lieu of anchor bolts
• Wall studs on interior faces to be finished
  • 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
• Narrow, or weak, returns 
  • Shall be addressed similarly to braced, exterior walls immediately above  

Narrow Return Remediation, Isometric

• Shall be defined as
  • An exterior wall at a corner (usually next to a garage door)
  • Less than 3 linear feet wide
  • See illustration Narrow Return Remediation, Isometric
    • Except that the address shall be modified as follows
      • Steel strap may be omitted for lack of depth in the crossing angle
      • Solid, full-depth blocking shall be at thirds
• The proximate header
  • Shall be extended tight to the 4-stud corner and
  • Supported at its terminus by not less than 1 jack stud
• The preservative-treated sill plate or mudsill shall be tripled
  • Therewith requiring a longer pair of anchor bolts
  • Therewith requiring a longer hold-down
  • Which extra two members shall be set BETWEEN studs and NOT BELOW them 

Comment:  This custom home designer has seen this common building mistake of a narrow return too often designed into a structure and not adequately compensated in his opinion. 

As a rule of thumb, a return (very most often in a garage at a house corner where the driveway-facing wall nearest that corner) should be 3 linear feet wide or more. 

Why?  Because about 6 linear inches of that 3 linear feet will go to conventional clad – more than that with masonry clad.  That leaves 2 1/2 linear feet at best for opening a car door and getting out…necessary and minimally sufficient space in the author’s opinion.

For another reference to reinforcing narrow garage walls, see "Practical Engineering: Building Strong Garage Door Walls" by Carl Hagstrom, Journal of Light Construction, April, 2004. 

Comment: In seismic zones above B, or 2, please consider relaxing nailing pattern of sheathing to members.  See local building authority having jurisdiction. 

• Plywood sheathing shall extend not less than 4 linear feet from the weak return’s interior jack stud
  • With not less than 16d deformed, galvanized nails
  • At not greater than 6 linear inches on center both ways 
  • Galvanized straps, not less than 1 ½ linear inches wide, not less than 20 gauge
  • Shall be applied between floors, attaching from top plates up to bottom plates
  • Shall be applied at headers at not greater than 32 linear inches on center
  • Shall be applied at each side of header studs for door and window openings or
    • Failing that for longer headers, then shall be applied as
      • Both as above and
      • Along the length of a header
      • At not greater than 32 linear inches on center
      • At multiple bearing studs, or posts, supporting load points, attaching bearing members on the vertical across
        • Top and bottom plates
        • End and head joists
        • Headers
        • Beams and
        • Similar
      • At each end-length member, e.g., header and stud, top plates and post
        • Fastening with not less than 10d common nails
      • At not greater than 2 linear inches on center
• Wall studs below point loads
  • Shall be not less than tripled
  • Shall be plated at not less than rows of 2-10ds at 12 linear inches on center faced nailed from each open side
  • Shall be braced both sides at not less than the midpoint