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PART ONE of THREE
- Ridge board must be at least same depth (or greater) as the plumb cut end of intersecting rafters.
- Check rafters installed 24″ O.C., or per plan. (i.e., 12″, 16″, 19.2″, or 24″)
- Rafters should be structurally sound, crown up, yet cause no noticeable hump in plane of roof
- Inspect all rafter cuts
- Plumb cuts should bear fully against ridges, hips, and valleys. Conditions where a rafter cut is too short or only a small portion bears on the structural member (heel or toe) must have a 3′ scab secured and braced at the affected end.
- Birdsmouths should bear snug at topplate with minimum-to-no saw overrun(s) and create a consistently straight ceilingline.
- Rafter tail length (horizontal plane measured from the outside edge of topplate) should permit eaves construction having a soffit depth of 12-24 inches, or per plan (typical box window overhang a minimum of 6 inches).
- Check collar ties on every other rafter (secure each connection using 3 nails), within 18 inches of bottom of ridge board. Use random-length 2×4 only.
- Purlins to be same dimension lumber as the rafters being supported
- The location of purlins to be per plan and in accordance with maximum allowable unsupported span tables in the residential code (or every 8′ of rafter span).
- Purlin brace every other rafter (secure each connecting using 3 nails). Check brace angle and bearing. Alternate purlin bracing may be used, as required.
- Purlin can be notched into each brace, or bear on a 2′ long 2×4 block – teed into top of brace (secure using 5 nails)
- Brace should be oriented at approximately 90 degree angle to the supported rafter(s)
- Splice common & jack rafters over a purlin with 4′ of overlap between top & bottom segments. If a purlin is not conveniently aligned, add a brace directly under the splice (ensure the limits specified in the maximum allowable unsupported span tables of the residential code are not exceeded)
- Splices in ridges, hips and valleys shall be gusset-reinforced scissor splices. Requirements include:
- 24″ scissor-splice, nailed top & bottom
- Minimum 4-foot OSB/Plywood gussets (minimum thickness – 7/16″) cut to the same depth as the rafter, on both sides of splice
- Braced directly under the splice and supported by bearing wall or structural beam
- Ridge board to be braced at ends and where possible. Brace to be T-blocked entire length
- Hips exceeding 14 feet in span must include a midspan brace. Any brace exceeding 6-feet in length must be T-blocked 2/3 the length.
- Braces are required under valleys anytime the member crosses over a topplate or structural beam (Any brace exceeding 6 feet in length must be T-blocked 2/3 the length). Cripples and studs under valley bracing to be doubled.
- Terminate ceiling joists (interfering with valley rafter installation) short of the valley. Header off to ceiling joists on either side. Use joist hangers and consider doubling up joists, if necessary
- Rafter bracing
- Check no roof members braced to ceiling joists or strongbacks over living space
- Note: Roof structure can be braced directly to garage ceiling joists only. A 2×8 or 2×10 layed flat and spanning a minimum 3 joists must serve as the base.
- While engineered beams can be installed flush on the topplate, solid-sawn beams must be elevated (floated) a minimum 1 1/2″ above the ceiling line, whenever bracing to a wall is not possible.
- Note: Floating beams may be installed with an orientation parallel, perpendicular, or on a diagonal to ceiling joists. Roof loads must transfer from each beam end to suitable structure which in turn transfers these forces to the slab/soil compression zone. When a beam is elevated excessively high – 2×4 outriggers (diagonal braces) may be added to either side of the beam to provide lateral stability during installation of the beam
- Note: An exception to the float beam restriction exists for beams suspended over garage areas. Solid sawn beams over garages may be installed flush with the topplate to minimize the size of tapered end cuts at exterior walls.
- Any brace exceeding 6 feet in length must be T-blocked 2/3 the length.
- Palm bracing is accepted practice as long as the palm provides secure, reliable bracing to all supported members.
- Gables
- Furr out 16″ O.C. or per plan in siding areas
- Gables over 4′ in height require a stiffener or strongback at cripples, with a diagonal brace secured to a structural beam or topplate
- Note: Gable structure can be braced to garage ceiling joists only
- Detached Garages & Covered Walks
- Build to the same standards and tolerances as the house framing
- Construct fireblock between home & detached garage. Locate at garage end or mid-span to home
- Separation of walkway beams must not exceed with the width of the sidewalk (typically 4-feet) between the house and detached garage. This ensures each midspan support column will rest on the flatwork below to fully support, stabilize and transfer roof loads to the soil below.