Brownbuilt 900 should be screw fxed 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||75||T17 - 14 - 10 x 75||50||Roofzip M6 x 50 HG-Z4|
|Steel||65||Tek - 14 - 10 x 65 or Tek - 12 - 14 x 68||20||Tek - 12 - 14 x 20|
* If sarking or insulation is used over the purlins or for wall cladding fixed 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 220.127.116.11. of the Dimond Roofing and Cladding Technical Manual.
The Limit State Load / Span Capacity Chart is based on 6 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.
- 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 by using 3 fasteners/sheet/purlin. If this is done, the distributed load capacities given in the chart should be reduced using a multiplying factor of 0.5.
Long spans may require the specification and use of side lap stitching screws.
Restricted access roof, 0.55mm G550 steel Brownbuilt 900 has a maximum end span of 2400mm and a maximum internal span of 3400mm. The following distributed load capacities apply.
|BB900||6 fasteners / sheet||3 fasteners / sheet|
|Serviceability||2.0 kPa||1.0 kPa|
|Ultimate||4.0 kPa||2.0 kPa|