Netting
Netting should be run across purlins and be tensioned to remove unnecessary sag. Fastening to timber should be with
either galvanised staples or 25mm clouts avoiding contact with the roofing, and to steel with flat head screws.
Fixings should be at 150mm centres on end purlins in such a way that the netting cannot pull past the fixing. Edges
of the netting should be tied together or twitched at 300mm centres and fixed to each purlin. Safety mesh should be
installed to manufacturers recommendations.
Roofing Underlay
Horizontal Application: underlay is unrolled across the roof parallel with purlins and secured as necessary. Joins should
be lapped by a minimum of 75mm and supported on netting if roof pitch is below 8 degrees for self supporting and
have the side edges supported on purlins.
Vertical Application: underlay is unrolled vertically up the slope of the roof from guttering to ridge and secured to the
purlins as necessary before laying the roof sheet and fixing down. Joins should be lapped by a minimum of 150mm.
Support such as netting or safety mesh must be used on pitches below 8 degrees, or when using self supporting
underlays on purlin spacings greater than 1200 mm.
When used under roofing, all underlays must be supported on wire netting or strapping at 300mm maximum spacings.
Self sufficient underlays can be used on purlins spacing up to 1200mm without support.
Underlay should overlay into the gutter at least 20mm and not more than 50mm, and avoid lapping into the water flow.
Maximum single underlay sheet lengths shall be 10m for bituminous and fire retarded kraft papers. Longer runs are to
be end lapped 150mm. Synthetic underlays have no limit on their run length.
In general it is recommended that prolonged exposure of the underlay to the weather is avoided by fixing the roofing
over the same day. Always follow underlay manufacturers recommendations.
