Fastener Design
V-Rib should be screw fixed to either timber or steel purlins. The use of the appropriate length of 12g or 14g screw will ensure failure by screw pull-out will not occur under loads within the scope of the Limit State Load / Span Capacity Chart.
| Purlin Type | Roofing Rib - Screw Length* (mm) | Roofing Rib - Designation | Wall Cladding Pan - Screw Length* (mm) | Wall Cladding Pan - Designation |
| Timber | 65 | T17 - 14 - 10 x 65 T17 - 12 11 x 65 Roofzip M6 x 65 HG-Z4 |
50 | Roofzip M6 x 50 HG-Z4 |
| Steel | 55 | Tek - 12 - 14 x 55 | 20 | Tek - 12 - 14 x 20 |
* If sarking or insulation is used over the purlins or for wall cladding fixing onto a cavity batten, into the stud, the screw length will need to be increased.
For screw size range and fastener / washer assembly refer Section 2.2.3.1 of the Dimond Roofing & Cladding Technical Manual.
The Limit State Load / Span Capacity Chart is based on 5 screw fasteners/sheet/purlin without the use of load spreading washers (except for Duraclad material, which must be fitted with either profiled metal washers and 36mm EPDM seals, or 32mm Weatherlok washers).
Profiled metal washers are recommended for use:
- On end spans, or large internal spans where the Ultimate Limit State distributed load is limiting. Contact Dimond for specific advice in these design cases.
- When required to enable the fixing system to accommodate the thermal movement of long sheets – see Section 2.1.3.4 Thermal Movement
- Wherever the designer wishes to ensure the risk of fastener over-tightening will not cause dishing of the crest of the profile rib.
Use in serviceability categories (1) or (2) can allow the reduction of fasteners to 3 screw fasteners/sheet/purlin. If this is done, the distributed load capacities given in the chart should be reduced using a multiplying factor of 0.6.
Long spans may require the specification and use of side lap stitching screws.
Dimond V-Rib Fastener Layout Options
Restricted access roof, 0.55mm G550 steel V-Rib has a maximum end span of 1600mm and a maximum internal span of 2400mm. The following distributed load capacities apply.
| V-Rib | 5 fasteners/sheet | 3 fasteners/seeht |
| End Span | 1600mm | 1700mm |
| Internal Span | 2400mm | 2400mm |
| Serviceability | 2.2 kPa | 1.3 kPa |
| Ultimate | 4.1 kPa | 2.5 kPa |
Dimond V-Rib Fastener Layout Options
