Building Construction Handbook, Eighth Edition

More economical for larger spans than with double rafters and ordinary purlins. Used where the sizeof purlins would be uneconomically large and/or an excessive number of struts, ties and hangerswould be required

Top and bottom flanges/chords aretypically 100

×100mm or

100

×75mm and struts

100

×75mm

125

×

50 rafter

225

×

32

ridge board

lattice frame orother compositebeam (see page 557)

Elevationon A

wall plateor padstone

internal loadbearing wall

125

×

50

ceiling joist

wallplate

external wall

space withinthe roof voidmaximised

trussedpurlin

The lattice frame can be faced with plasterboard or with plywood for additional strength.

Trussed Purlin Roof