Spans for Joists, Rafters and Beams
(1) Except as required in Sentence (2) and Article 184.108.40.206., the spans for wood joists and rafters shall conform to the spans shown in Tables A-1 to A-7 for the uniform live loads shown in the Tables.
(2) Spans for floor joists that are not selected from Tables A-1 and A-2 and that are required to be designed for the same loading conditions, shall not exceed the design requirements for uniform loading and vibration criteria.
(4) Spans for roof ridge beams shall conform to the spans in Table A-12 for the uniform snow load shown.
Article 220.127.116.11 Ontario Regulation 332/12 Building Code, Information published by oncodes.ca for educational purposes only.
Joists : Joists uses wood, steel or concrete beams and are set parallel from wall to wall or across or abutting girders to support a floor of ceiling
Rafters : Rafters are structural components of a roof on a building. Traditionally, rafters are cut to sizes and land on a ridge board, which runs across the length of the building. Ceiling joists then connect the rafters and exterior walls, producing a vaulted ceiling filled with insulation and drywall to finish the space. Alternatively, it can be left as open space in an attic.