In Plain Language

This clause simply prohibits using cellular (lightweight, aerated) concrete masonry units in below-grade or weather-exposed applications, since that material isn't durable enough for contact with soil or the elements.

This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.