For a fuller explanation of this refer to the nz metal roof and wall cladding code of practice.
Purlin spacing for metal roof nz.
Do all roofing projects require purlins.
It should be noted that timber purlins for metal roof cladding are minimum 70mm x 45mm h1 2 18 moisture content and that battens used previously for tiles must not be used.
The adjustable cleat can be rotated up to 15 degrees from normal to accommodate the change in angle from vertical portal to the roof slope of the rafter.
Ridge boards were 25 mm 1 wide with a depth dependent on the rafter size.
For heavier material such as gage steel the metal roof purlins spacing length could go up to 4 feet.
Purlins up to 1200mm spacing must be fixed with a 1 10g 80mm long purlin screw minimum or a pryda purlin strap bs 70.
This result should be referenced to the wind load span design graphs.
The purpose of the purlins is to provide a solid foundation for the metal roofing panels and trim to be screwed to.
We do recommend it however.
Fastener patterns on nzs 3604 buildings should be consistent throughout the roof excluding top and bottom rows.
Two nails maybe preferred to prevent batten rolling over with high roof pitches.
If the space between posts is greater than 8 feet then brace is needed to avoid buckling.
For the lighter material such as lightweight aluminum the common spacing length is 4 inches of clear gap.
By the standard the most used placement of purlin span for metal roof is five foot intervals.
Purlin batten purlin batten fixing type d 3 45kn 2 blue screws or 2 skew nails plus 2 wire dogs for purlin on edge fixing type c 2 4kn purlin batten 1 blue screw 2 nails fixing type b 0 8kn purlin batten fixing type a 0 55kn 1 nail purlin batten note.
Purlins typically 75 x 50 mm and fixed across the rafters were spaced at 760 900 mm centres depending on the roof cladding.
If a design quotes wind speed in m s ask for a roof plan showing design loads and purlin spacing apply serviceability loads for pierce fastened products ultimate loads for clip fastened profiles.
The purlin spacings should be limited to the lower of the trafficable limitations and design wind load with the capacity of the structure.
For 2x4s purlins the posts are spaced in 4 feet distance.
Rafters were birdsmouthed over the top plate and extended beyond the wall framing to create the eaves.
Where the end purlin spacing is less than 800mm an adjustable end brace with a bolted end cleat is available as twisting of the end cleat is not practical.
