Flat Roof Construction < = 3 °

1. Fix the Purlins as described for the more usual roof slopes, but exercise caution when laying the roof deck and make sure that the roof Purlins are normal to the roof slope before fixing the decking to them. This can be achieved by using PurlinTies on all spans in excess of 4.5 metres, see requirements table.

2. For "built up" roof design using multi-spanning decking, our solution requires that the Purlins are fixed as opposing pairs and restrained by using supports bolted between Purlin pairs. Diagram 2 illustrates this method. We recommend that the supports are used on all Purlin spans exceeding 5 metres. This ensures that a stable working platform has been constructed and eliminates the need for eaves restraint.

PLEASE NOTE: There is a risk of 'ponding' on very shallow roof designs.

Some proprietary decking systems have a low deflection tolerance.

If specifying cladding which provides little or no restraint to Purlins then refer to Unrestrained Roof Construction table (link).

CLEAT LOCATIONS

A= Required Purlin centres PLUS one Purlin top flange width.

B=Required Purlin centres LESS one Purlin top flange width.

The above formulas place the top flange centre line of each Purlin equidistant. When Purlins are used in this manner, no Eaves Restraint is necessary.