Further assistance may be obtained by contacting Duggan Profiles on +353-56-7722485
In roof situations the top flange of the purlin requires restraint to help resist the torsional effects generated by positive loading. Where screw fixed cladding such as single, double or composite products are used this support is achieved through the binding effect of cold rolled to cladding created by the fixings used. Where non-restraining cladding systems are used this support does not exist and so must be provided by alternative means. Non-restraining cladding may be used as a general term to describe any roof cladding material that does not resist the torsional tendencies of purlins under load. Such materials can include standing seam profiles where the product is fixed via secret fix support brackets (halters) to the cold rolled. No through fixings are used and support for the top flange is limited to whatever frictional resistance exists between the halter and the seam. Other materials that are generally considered non restraining include Fibre Cement and Tiles/Slates.

A determination on the restraining capabilities of a cladding product may be difficult to determine and somewhat subjective. The advice of the cladding manufacturer should be taken into account and where doubt exists the anti sag support system for non restraining cladding should be used.

If Tiles/Slates are fixed on top of a restraining system such as a steel deck of sufficient thickness they may be considered restrained. In such cases the advice given in the section Additional requirements for long slopes, steep slopes or heavy cladding during installation should be applied.
Use of Load Tables with non restraining cladding
The standard Load Tables assume the top flange is fully restrained and may NOT be used where non restraining cladding is involved. A separate set of tables is available for this situation. These make allowance for the unrestrained nature of the flange. Please contact Duggan Profiles for appropriate loadings.
Anti sag support requirements for non restraining roof cladding
When non restraining cladding is used the anti sag components form an integral part of the structure post installation as well as resisting sag during roofing. Angle Struts must be used as Tube Struts do not provide adequate support to the compression flange. If a heavy roof load such as tiles is involved the Angle Struts may require support from Tie Ropes at intervals along the slope. These transfer portions of the down slope load to the rafters and prevent buckling of the Angle Strut. The following construction details categorised by the distance spanned show the general configuration of components. It should be noted that the number and location of Tie Ropes will vary depending on the loads involved. Please consult Duggan Profiles for further guidance.
Construction details:
Span (M): Up to 6.1m

For spans up to and including 6.1m anti sag supports are recommended at:
Mid span
Components: Angle Struts are used to support the purlins with the load transferred to the structure by a combination of Apex Ties and Tie Ropes.
Note on above: Supports are generally not required for spans less than 3m 
Restraints for Bays over 6.1m up to 9m
Span (M): 6.1 - 9m
For spans greater than 6.1m up to and including 9m anti sag supports are recommended at:
1/3 points
Components: Angle Struts are used to support the purlins with the load transferred to the structure by a combination of Apex Ties and Tie Ropes.