No modifications!
Under no circumstances are roof trusses to be modified on-site. If trusses are forced to work in ways they were not designed for, problems will develop.
![Diagram showing the effect on a roof truss of one of the bottom chords being cut away.](images/page_002_roof_trusses_on_site_cautions_4.gif)
Cutting the bottom chord will cause the other parts to work
more in bending than axial loading. The truss will sag and break.
![Diagram of the effect on a roof truss of a web cut.](images/page_002_roof_trusses_on_site_cautions_5.gif)
Cutting a web will cause the truss to be no longer a pattern of rigid triangles.
The truss will become unstable and distort out of shape.
![Diagram showing the effect on a roof truss of the middle being wrongly supported by a wall.](images/page_002_roof_trusses_on_site_cautions_6.gif)
The bottom chord is designed to work mainly in tension. If the middle is wrongly
supported by a wall, the chord will be put into bending. The truss may break.