BEFORE THE ARCHITECT – CUSTOM HOME DESIGNING BACKGROUND – HOUSE DESIGN ARTICLES
DREAM HOME DESIGNING -
WOOD STUD FRAMING WALL CONSTRUCTION
By Before The Architect Copyright 2009
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YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION
Associate only with the best - better than you at whatever it is – the greater the disparity, the more valuable the association. Before The Architect
Almost everybody’s got ‘em – wood stud framing wall construction. They’re the bones of almost all homes in the US. Building them is mostly regarded as commodity work.
Did you know that the design of wood stud framing walls can vary widely – to the benefit or bane of owners? Home builders will bring their own standards or you can set yours.
This article is about setting your own wood stud framing 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, that 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 high-stress structures.
DESIGN STANDARDS FOR WOOD STUD FRAMING WALLS
Mudsills and sole plates for exterior walls, when in direct contact with masonry, shall be preservative-treated.
Wall stud framework spacing shall not exceed 16 linear inches on center and shall be placed with its wider faces perpendicular to wall lines.
Top plate butt joints – both upper and lower top plates - shall be supported by not less than 1 stud set to share both butts equally; 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; and shall be continuous over cripple stud framework
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.
Notches and Bores
In wall stud frames, notch depth shall be limited to 20% of the actual (not nominal) stud frame depth whether load-bearing or nonload-bearing.
Bored holes in nonload-bearing stud frames shall be limited to 40% of actual (not nominal) stud frame depth; shall be limited to 60% of the actual (not nominal) double- stud frame depth; and shall be on-center.
Bored holes in load-bearing stud frames shall be limited 20% of the actual (not nominal) stud frame depth; shall be limited to 60% of the actual (not nominal) double-stud frame depth; and shall be on-center.
A notch or a bore shall not be made within 3 linear inches of a butt; shall not be made within the middle third of a member as measured in length not width; shall not occur in the same stud. Only one notch or (not “and") one bore shall occur in the same stud
Comment: That is, neither top plate member’s butts shall be unsupported by a stud framework– 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 frame on which both butts should share space atop . . . . .
Top Plate Butt Joint, Unsupported - Wrong
Exterior, right-angle corners shall be built of not less than 4 stud frames, laid out as depicted in Four-Stud Framework Corner, Section in Plan View, of not less than 2x6 members. In no instance shall there be an uninsulated void in a wood stud frame wall, notably out-facing but not to the exclusion of in-facing or, as in this section drawing, side-facing, too.
Comment: This custom, fine home designer prefers that all corners be built this way, but that’s just him.
Four-Stud Framework Corner, Section in Plan View
Stud frame 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 stud framework 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. Failing these standards, then solid full-depth blocking shall be applied at not less than midspans and at not greater than 4 linear feet on center for bracing, noting that such blocking may be applied independently for fire-blocking.
Braced exterior wall on L1 shall be fastened to code, except that nailing shall be with not less than 16d sinkers.
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 and may change for high wind-resistant locales, as well.
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.
Supply and Valve Lets
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. When not less than 4 linear feet in clearspan or when acting as shearwall, headers shall be trimmed at each end by double king stud frames and shall be supported by double jack stud frames, or jamb stud frames, or trimmer stud frames; when less than 4 linear feet in clearspan or when acting as shearwall, headers 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 framework and supported by not less than a single jack stud framework, or jamb stud framework, or trimmer stud framework 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, headers shall be run tight to the corner structure. Headers shall not be severed or otherwise amended throughout as, e.g., by butting to a window sill plate top of face.
Jack Stud Framework at Window Sill Plate, Severed - Wrong
Comment: The jack stud frames’ 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 Framework at Window Sill Plate, Severed - Wrong.
In interiors 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 frame 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 of a header, either a foam insulation or air space shall be set to the interior face.
In bearing application, a header 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 interiors around the big window with the swell view.
Header 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; shall be tight to top plates in a braced wall segment or cripple stud framework which framework is arranged in common spacing and flush to both jack, or trimmer, or jamb stud framework; and shall be steel-strapped securely fastened to both top plates, header, and not less than 18 linear inches of jamb, or jack, or trimmer stud framework at each end.
Anchor bolts shall not be less than 2 per braced wall segment; 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).
Holdowns shall be at both cornered faces and not just the short face; shall be braced at interior walls at L1 and L2 and above; shall be membered and fastened as in immediately above. Exception: 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. Exception: Not less than 5/8 linear inch carriage bolts may be applied in lieu of anchor bolts.
Wall stud frames on interiors faces to be finished shall not be greater than 1/16 linear inch difference between any three on their shared planes; shall be shimmed level for not greater than 1/16 linear inch difference between any three on their shared plane.
Narrow, or weak, returns
Narrow returns, or weak returns, shall be addressed similarly to braced, exterior walls immediately above.
Narrow Return Remediation, Isometric
Narrow returns shall be defined as an exterior wall at a corner (usually next to a garage door) less than 3 linear feet wide. See illustration addressing 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 framework 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 and 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 ˝ 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 stud framework 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 - fasten with not less than 10d common nails at not greater than 2 linear inches on center.
Wall stud frames 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; and shall be braced both sides at not less than the midpoint.
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