Pitch

The minimum pitch is the roof cladding pitch and not the building design roof pitch. The allowable cumulative deflections of the frame, purlin, and roof sheeting require the building design roof pitch to be increased to comply with minimum cladding pitch.

Plastic roof lighting profiles deflect more than metal roof or wall claddings of the same dimension.  See Deflection. 

The COP recommends that the roof pitch for plastic roof lighting profiles is increased to more than the minimum for the profile, in addition to that recommended for allowable deflections (1.5°).

It is better practice that all plastic roof lighting profiles with sheets longer than 15 m should be a high rib profile (more than 35 mm) or that the roof pitch should be increased by 3° over that required in Minimum Roof Cladding Pitch.