The Ontario Building Code | Concrete Topping
188.8.131.52. Concrete Topping
(1) Except as permitted in Sentence (2), where a floor is required to support a concrete topping, the joist spans shown in Table A-1 or the spacing of the members shall be reduced to allow for the loads due to the topping.
(a) is 38 to 51 mm thick,
(b) is normal weight,
(c) is placed directly on the subflooring="http://thehandyforce.com/flooring/" title ="Handyman flooring install Toronto">flooring, and
(d) has not less than 20 MPa compressive strength after 28 days.
(3) Where a floor is required to support a concrete topping not more than 51 mm thick, the beam spans shown in Tables A-8 to A-11 shall be multiplied by 0.8 or the supported length of the floor joists shall be reduced to allow for the loads due to the topping.