Spans for Joists, Rafters and Beams

(1)  Except as required in Sentence (2) and Article, 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.

    (3)  Spans for built-up wood and glued-laminated timber floor beams shall conform to the spans in Tables A-8 to A-11.

    (4)  Spans for roof ridge beams shall conform to the spans in Table A-12 for the uniform snow load shown.

Article Ontario Regulation 332/12 Building Code,   Information published by 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.