ROOF AND CEILING FRAMING RESEARCH

Roof framing quality
Good roof framing comprises:

• H3.2 for roof framing exposed to the weather
• H1.1 or KD untreated for enclosed roof framing
• H1.2 for skilllion roof framing
• H3.1 for low slope membrane clad roofs
• H1.1 or KD untrated for roof sarking
• H1.1 or KD untreated for ceiling framing
• Framing member sized and spaced in accordance with NZS 3604.  Rafters should be stored correctly and allowed to dry before being erecte. If rafter are installed green, especilly if 200 mm or deeper, they should be supported from underneath until dry to restrict bowing and sagging 
• Member fixed to resist wind uplift forces
• Member installed with any bow upwards
• Framing joined over a supporting member or loadbearing wall
• Being erected straight and true

Rules for setting out is important to getting a roof structure accurately built can be a time consuming process.(getting accurate angle and cuts)

Rules for setting out a roof are:

• Ridges are parallel to wall plates
• Common, jack and cripple rafters are at right angles to wall plates
• Hips and valleys bisect the corners formed in the external wall framing
• Short hip rafters connect different height ridges
• The highest point of the roof is over the greatest span.

The first steps to correctly set-out a framed roof are to:

• Locate the position of hips, ridges and valleys on the wall framing 
• Mark the position of the main roof members( hips and common rafters to each the ceiling joist) set-out on the top plate whe the set out for the studs is being done, i.e before the walls are erected
• Evenly space other rafters between the main rafters
• Mark the position of the ridge on the top plate
• Transfer rafter positions from the top plate to the ridge board

Erecting roof framing (to erect the roof framing)

• Check the wall framing(i.e walls are parallel at the top plate level), the top plate is straight, walls are plumb and adequately braced
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• Make a common rafter pattern and use it as a template for all other common rafters
• Fit strutting beams, struts and under purlins and any other permanent supports to rafters or ridge
• Put in place and temporarily support a common rafter, and fix rafter to top plate(ususlly a two person job or more if require)
• Erect opposing rafter and fix to the top plate
• Do the same at the other end of the roof to suit the length of the ridge
• Lift ridge into place and fix between the rafters
• Plumb and temporarily brace the end rafters
• Install end common rafters 
• Install hips, short ridges, valleys and remaining common raftes
• Check regularly to ensure the ridge, hips and valleys remain straight
• Fit collar ties or cleats as rafters are fixed into final position
• Fix cripple and jack rafters in place
• Fit bracing when roof checked for square and plane and before removing temporary bracing.

Roof framing terms

Connecting rafters to top plate

• Fix rafter top plate with 2/100 x 3.75mm skew nails, plus wire dogs in accordance with NZS3604 for the rafter span and wind zone
• Rafter -nail also to ceiling joist
• Fix ceiling joist to top plate with 2/100 x 3.75 mm nails
• Nogs -cut between ceiling joists
• Birdsmouth to form 32mm min. landing (50mm recommended) for rafters on top plate
• Not less than 80% of rafter depth or 65mm min.
• Fix rafter top plate with either 2/100 x3.75mm nails, and wire dogs or U-strap
• Rafter -birdsmouth to provide 32mm (50mm recommended) landing to top plate
• Nogs- if ceiling fixed to underside of rafter

Fixing rafters at ridge

• Fix rafters to ridge board with min. 2/100 x 3.75mm nails - where wire dogs required in NZS 3604 Table 10.2 provide to additional nails

Connecting trusses to top plate 

• 2/100 x 3.75 mm nails plus wire dogs as required by NZS 3604
• Two wire dogs to connect top plate to stud( at 900mm max crs for light roofs in high wind ares)
• 27 x 1.2 mm galv. ms strap with 10/30 x2.5 mm nails to both truss and stud in some high uplift cases

Bracing trusses during erection

• Mark truss location on top plate before erecting wall framing
• Ensure bottom plate securely fixed before fixing brace