Civil Engineering Reference
In-Depth Information
Openings in attic trussed rafter roofs can be formed in a similar manner to those shown in
the traditionally constructed roof section, Chapter 3. Using two or more trussed rafters as
trimmers, both infilled rafters and floor joists need to be supported from those trimming
trusses. Short purlins are used to pick up the ends of the trimmed rafters, the purlins them-
selves being supported on girder trusses. The purlins should be supported on purlin posts
built in to the attic girders at the lower purlin level, and supported on the ceiling tiles as
close to the joint between top chord and ceiling tie as possible for the upper purlin. The
purlin should be notched under the top chords to give an adequate birdsmouth for the on-
coming infill rafters. The purlins will of course carry the infill rafters, leaving the floor
joists to be infilled. This can be done using short lengths of floor joists of a matching
depth to the bottom chord of the trussed rafter fixed across the
