Ontario Building Code Practice Exam 2025 - Free Building Code Practice Questions and Study Guide

The minimum thickness required for a concrete slab in a residential building is 100 mm. This thickness is deemed necessary to ensure the structural integrity and load-bearing capacity of the slab, preventing issues such as cracking and inadequate performance under load. A 100 mm thick slab gives a balance between providing sufficient strength and being cost-effective.

Options with lesser thickness, such as 75 mm, may not provide the needed performance characteristics for residential applications, as they may be susceptible to deformation and cracking under typical loads. On the other hand, while 125 mm and 150 mm may offer additional strength, they might be considered excessive for standard residential uses, leading to increased material costs without significant benefits for typical home construction. Thus, the standard adopted is 100 mm for its practicality and compliance with the requirements outlined in the Ontario Building Code.