Civil Engineering Reference
In-Depth Information
Small openings for flues or loft hatches are dealt with in Chapter 7 under the appropriate
headings. Details below apply to large openings, i.e. those greater than two standard
trussed rafter spacings. Such openings can be provided using specially designed girder or
compound trusses either side of the opening, or by taking support from the structure itself,
in which case special trusses will be required for the infill area.
On the true trimmed opening, a purlin or purlins must be fitted between the girders onto
which common rafters are fixed. The ceiling joists will be supported on a purlin at bottom
chord level on the girder truss. All purlins and binders must be fixed to the trussed rafters
at the node or joint points. It is good practice to have the common infill
