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Selecting Trussed Rafter Profiles
Determination of the required truss rafter profile assumes the ability to read a two dimensional drawing and visualise the required structure in three dimensions.

This skill is acquired by experience, although certain powerful graphical aids in the form of computer programs are now available to assist the designer in
this area.
The designer's task is to take the roof plans, sections and elevations presented to him by his client and form the required roof shape in his mind. The technique of 'sectioning' the roof will then give the required profile of the truss required at any point.
'Sectioning' requires the designer to consider the height dimension of a particular point on the roof line, as well as its plan position. The profile change
points for a truss are often seen on the roof plan as hip or valley intersection lines, or at points where the apex or eaves line changes in some respect.  The following figures illustrate the transition from two-dimensional roof plan to three-dimensional impression of the roofscape to the required trussed rafter profiles.