Building Construction Handbook, Eighth Edition

Trussed Rafters ~ these are triangulated plane roof frames designed to give clear spans between the externalsupporting walls. They are delivered to site as a prefabricated component where they are fixed to the wallplates at 600mm centres. Trussed rafters do not require any ridge board or purlins since they receive theirlateral stability by using larger tiling battens (50

¾

25mm) than those used on traditional roofs.

Longitudinal ties (75

¾

38) fixed over ceiling ties and under internal ties near to roof apex and rafter

diagonal bracing (75

¾

38) fixed under rafters at gable ends from eaves to apex may be required to provide

stability bracing † actual requirements

specified by manufacturer. Lateral restraint to gable walls at top

and bottom chord levels in the form of mild steel straps at 2„000 maximum centres over 2 No. trussedrafters may also be required.

Timber Pitched Roofs up to 7.5 m Span--Types