The B5 metric corrugation profile is a more modern profile than the traditional 3 inch profile so can be used to a lower pitch and with smaller overlaps. The sheets are approximately 40% wider, offering a better coverage per sheet. B5 is available in 14 lengths from 4′ to 10′ 6". B5 can be used to refurbish buildings clad in 3 inch sheets utilising ‘existing purlin centres’. All existing 3 inch sheets will need to be removed, it is not possible to replace individual 3 inch sheets with B5.
http://www.cembrit.co.uk/roofing/corrugated-sheets/cembrit-b5/