STRUCTURAL DESIGN FOR ARCHITECTURE

Structural Design for Architecture

Fig. 6.45 Section through truss-and-purlin roof. The

purlins are positioned so that the 'common' rafters lie

in the same plane as the top elements of the trusses.

An alternative to trussed-rafter construction

is purlin construction in which plain rafters are

supported on a series of secondary beams,

called purlins, which run parallel to the direc-

tion of the ridge. The purlins can be supported

on trusses or cross-walls of timber-stud or

masonry (Figs 6.44 to 6.47). Where trusses are

220 used they are usually spaced 2 m to 3 m apart.

Fig. 6.44 Truss-and-purlin roof. In the truss-and-purlin

system fully triangulated trusses support purlins which in

turn support common' rafters.

Purlin

Binder

Tie

Wall plate

Truss

Common rafter

Purlin

Rafters

Pack nailed

in position

Ceiling joists Hanger

Strut

Ceiling

binder