COP v3.0:structure; maximum-span-and-fastener-requirements

3.16 Maximum Span and Fastener Requirements 

3.16.1 Purlin-Rafter Connections 

For sprung curved roofs, the purlin/rafter connection must be increased at the eaves.

Long lengths of pierce fixed roofing will impose added loads to the purlin connection due to thermal movement of the roof.

3.16.1A Purlin to rafter fastener requirements for SG8 Radiata pine, complying with NZS 3604:2011

 Use 70 x 45 mm radiata pine on flat minimum
 Use 90 x 45 mm radiata pine on flat minimum
Rafter SpacingPurlin SpacingLow Wind ZoneMedium Wind ZoneHigh Wind ZoneVery High Wind ZoneExtra High Wind Zone



3.16.1B Purlin to Rafter Fastener Fixing Capacity

TypeFastenerFixing Capacity (kN)
A1/90 x 3.15 gun nails0.55
B2/90 x 3.15 gun nails0.80
C1/10g x 80 mm self-drilling screw2.40
D2.10g x 80 mm self-drlling screws3.45
E1/14 g X 100 mm self-driling screws5.50

3.16.2 Sheet Overhang 

The maximum overhang for all corrugate and low trapezoidal profiles is 150  mm, unless a product has been specifically tested to withstand point load and design wind loads at a greater overhang.

The allowable overhang distance of various cladding profiles will depend on their section properties.

When using trapezoidal profiles, greater overhangs can be achieved by stiffening the edge of the sheet in various ways; the most common being using a square gutter with a horizontal flange, but this should be fastened on every pan to achieve continuity.

The limit placed on low trapezoidal profiles with a stiffened overhang is 300 mm but it is not suitable for corrugate.

The overhang distance can be increased for some trapezoidal profiles with a rib height greater than 28 mm, but this distance must be proved by testing.

Where the cladding is fixed at a ridge or apron, the overhang distance can be increased to 250 mm from the end of the sheet, as the cladding is not subjected to the same point load or UDL and the load is shared with the flashing.

Point of access and expected roof traffic loads must also be considered.

3.16.3 Maximum Spans for Corrugate Wall Cladding 

The maximum span for pan fastened wall cladding is generally governed by temporary deflection under load, rather than permanent deflection around the fastener.

3.16.3A Maximum Span for Wall Cladding: 5 Fasteners per Sheet (every second trough)

*Serviceability load governs 
The deflection criteria used in this table is span/120 + P/20, where P = the space between fasteners. Higher deflection limits may be acceptable in certain circumstances.
Wind ZoneLoad (kPa)*Maximum Spans
0.40 mm0.55 mm
Very High1.721.401.60
Extra High2.091.201.50

3.16.4 Fastener Patterns 

Fastening patterns for the most commonly used profiles are designated in the following manner.





These fastening patterns should be used in conjunction with load span graphs.

The load on a purlin and a purlin/rafter connection is determined by the wind load and the area of roof the load is acting upon. Roof fasteners transfer wind uplift-loads to the purlins, which in turn transfer them to the primary structure.

Fastening to every second purlin may be within the roof's load/span range, but will double the load acting on the fastened purlins. All purlins must be fastened to unless alternate purlins are specifically designed to take the additional loads