Roof timbers

Minimum dimensions of roof timbers shall beRafters not exceeding 7 ft. long 2 in. x 4 in. at 30 in. centre. Rafters not exceeding 16 ft. long 2 in. x 4 in. at 24 in. centre. Rafters exceeding 7 ft. in length 2 in. x 6 in. at 30 in. centre. Purlins 1 in. x 4 in. spaced at 2 ft. centres. Purlins 1 1/2 in. x 4 in. or equal if over 2 ft. centres.