The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
Pan fixing can be used for roof as well as wall fixing provided certain fixing conditions are met:
- Light coloured roofs are limited to 12 m, thereafter with sliding washers and crest fixed.
- Dark coloured roofs are limited to 8 m, thereafter with sliding washers and crest fixed.
- If the insulation is laid close to the roof cladding, deduct 4 m of pan fixing from the above.
- If the ceiling is insulated, the roof cavity should be vented by a ridge ventilator or other permanent vents.
- Metal roofs that are not post painted should be regarded as dark coloured due to the oxidation and change in colour and surface over time.
- Translucent fibreglass sheets can be pan fixed for 8 m then crest fixed with sliding washers for 4 m, limited to a maximum of 12 m.
- Fasteners should be a minimum of 12 x 20 mm self-drilling for steel purlins and 12 x 40 mm for timber, both using a 25 mm metal and sealing washer.
- All fasteners should be driven snug tight with a torque driver or depth locator.
- Fasteners should be placed within 50 mm of the rib of the sheeting but allowing 25 mm clearance for water egress.
N.B. The pullover design values established by testing for pan fixing are more than twice those for crest fixing.
All sheets should have full bearing on all purlins that they cross to ensure a positive seal. Care should be taken to fix at right angles to the roof, and purlin flange alignment is critical if purlin creasing is to be avoided.
Corrugate and symmetrical profiles should not be pan fixed for roof cladding.
A limited amount of movement between the fastener and the cladding can be provided with an oversized hole for the fastener. When a greater amount of expansion is required, sliding fixings are necessary to allow for expansion and contraction. (see table 4.1.6)
There are two main types of sliding fixings.
- Sliding Washers
- Sliding Roofs
Sliding washers are used where the sheet and the fastener are separated by a material with a low friction coefficient, such as Teflon, enabling them to move independently in elongated holes. N.B. The seal should be made between the roof cladding and the washer by placing the sliding face (Teflon) upwards and the sealing face down onto the cladding.
Without lap stitching the wind and point load performance will not comply with the load span graphs in 3.14.5 Wind Load Span Graphs