During cladding installation cold rolled members will be subjected to loading from materials, manpower and equipment all of which will cause some degree of sag. This is undesirable as the accuracy of purlin installation affects sealing of cladding joints which in turn influences air leakage. Whilst some of this loading will be temporary in nature and the effect of any distortion lessened by the bracing effect of screw fixed cladding, consideration nonetheless should be given to the inclusion of anti sag support. This helps minimise sag and achieve straight sheeting lines. The following work practice should also be observed. Cladding should be installed starting at the rafter and progressing towards the centre of bay with all sheeting fully fixed as it is laid. This helps restrain the coldrolled members. 

The chart below provides guidance on the requirement for anti-sag supports during cladding installation. This is applicable where either Tube Ties or Threaded Rod Ties are used.
Caution: This chart provides simplified guidance and must be read in conjunction with the terms of use listed underneath.  

Roof slope (°)	Purlin section	Bay centres (m)
		Up to 6.1	Up to 7.5	Up to 9
4 - 10	Up to 265	0	1	2
10 - 20	Up to 265	1	1	2

The information contained above may be applied subject to the following restrictions and conditions.

• The guidelines apply where screw fixed steel sheeting is used. The cladding used must provide full restraint to the top flange of the purlin.

• Tube Ties or Threaded Rod Ties may be used with the sections listed above.

• For sections greater than 265 the more substantial support provided by Angle Struts is recommended. The frequency of use is dependent on bay centres and is generally similar to that listed in the table above however please contact Duggan Profiles to discuss specific cases.

• There are additional requirements for roofs over 20° or slope lengths greater than 20m to avoid overloading the anti sag components. Refer to Additional requirements for long slopes, steep slopes or heavy cladding during installation.

• The information outlined above is suitable for managing deflection during cladding installation. They may not be applied where wind uplift may be an issue and equally should not be used where heavy roof loads or non restraining cladding leave the top flange under restrained. Refer to Anti sag support for wind uplift and Anti sag support for non restraining roof cladding for appropriate recommendations.

• Apex Ties are required in all situations where anti sag ties are used.If this is not possible some other form of anchor support such as Tie Ropes must be used. Refer to Additional requirements for long slopes, steep slopes or heavy cladding during installation for details on use of Tie Rope in roofs.

• There are additional requirements for roofs with a single slope. Refer to Additional requirements for Mono Pitch Roofs.

• These guidelines are not applicable to flat roofs (pitch < 4°). Refer to Anti sag requirements for Flat Roofs.

Where anti sag ties are to be used they are applied as indicated in the following diagrams.

In the general “A” roof situation purlins are tied to standard Apex Ties spanning the apex using either Threaded Rod Ties or Tubular Ties. Where this is not possible (eg. where a Mono Pitch Roof is used) an alternative means of support must be provided. An adapted version of the standard apex tie may be feasible as shown here.  

In principle this is similar to that used on standard roof applications where the cladding provides adequate restraint to the top flange of the purlin. Tube Ties or Threaded Rod Ties may be used in conjunction with an Apex Tie. Where circumstances prevent the use of a standard Apex Tie an alternative may be used as outlined in Additional requirements for Mono Pitch Roofs. This effectively allows the roof to be treated as separate sections with each tied to an individual support. Tie Ropes may be needed if heavy loads or long slopes are involved and if required they are applied in the same manner as for the standard application. Refer to Additional requirements for long slopes, steep slopes or heavy cladding during installation for further guidance on the application of Tie Ropes in roofs.

Caution: Due to the constantly changing gradient of the slope Tube Ties will not fit in succession as is normally the case. Instead the offset arrangement shown in the diagram below can be used. Threaded Rod Ties are fitted in a similar manner.  

On longer slopes it may be more difficult to maintain accurate sheeting lines using the normal anti sag arrangement due to the extra weight tending to slide off the roof. A similar issue may arise on steeper slopes. When the cladding is fixed this is not a problem as its weight is transferred to the rafters by the diaphragm action of the sheets. The problem may be minimised by starting sheeting at the rafter and fully fixing the cladding as it is laid. Where additional support is required Tie Ropes can be added at intervals along the length of the slope to transfer a portion of the load to the main structure. The table below lists guidance for the more common situation. For more comprehensive details please contact Duggan Profiles for advice.

• The information contained above may be applied subject to the following restrictions and conditions. It is also advisable to seek guidance from Duggan Profiles as the information provided is of a general nature and inadequate to cover all possible scenarios.

• The guidelines apply where screw fixed steel sheeting is used. The cladding used must provide full restraint to the top flange of the purlin. For roofs over 20° or sections greater than 265 Angle Struts should be used instead of Tube Struts. It is also advisable to contact Duggan Profiles as the frequency of Tie Ropes may need to be increased.

• The information outlined above is suitable for managing deflection during cladding installation. They may not be applied where wind uplift may be an issue and equally should not be used where non restraining cladding leaves the top flange under restrained. Refer to Resisting the torsional effects of wind uplift and Resisting the torsional effects on under restrained top flange for appropriate recommendations.

• Apex Ties are required in all situations where anti sag ties are used. If this is not possible some other form of anchor support such as Tie Ropes must be used.

• These guidelines are not applicable to flat roofs (pitch < 4°). Refer to Anti sag requirements for Flat Roof.

Note: The advice presented in this section refers to situations where a combination of long slopes and the weight of cladding (or steep slopes and the weight of the cladding) create down slope forces during installation that can't be managed by the standard anti sag arrangement hence the need for Tie Ropes. It is assumed that post installation the diaphragm action derived from the cladding adequately restrains the coldrolled sections. This must not be confused with non restraining heavily laden roof situations where Tie Ropes and Angle Struts form an integral part of the structure post installation as well as during roofing. For anti sag requirement for this situation please refer to Anti sag support requirements for non restraining roof cladding.