The Ontario Building Code | Heat Transfer Performance
9.7.3.2. Heat Transfer Performance
(1) windows, doors and skylights described in Clause 9.7.1.1.(1)(a) and their components shall be designed, constructed and installed to,
(a) minimize surface condensation on the warm side of the component, and
(b) ensure comfortable conditions for the occupants.
(2) Compliance with the heat transfer performance requirements described in Sentence (1) shall be demonstrated by,
(a) compliance with the requirements in Article 9.7.3.3., or
(b) design and construction conforming to Part 5.
In Plain Language
Windows, doors, and skylights must meet minimum heat transfer (energy efficiency) performance levels, limiting how much heat escapes through these typically less-insulated parts of the building envelope.
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.