← Ontario Building Code FAQ
OBC DIVISION B · PART 9 · SECTION 9.6 — GLASS

Is there a maximum glass size or thickness rule for houses in Ontario?

Yes. Glass must be a type and thickness appropriate to its area and exposure, chosen from CAN/CGSB glass standards and Part 9 sizing provisions, so larger panes and windier or more exposed locations require thicker or stronger glass.

Code reference
Glass types must conform to the applicable CAN/CGSB glass standards, and the maximum area of individual panes is limited according to glass type, thickness and exposure to wind load. Larger panes require greater thickness or stronger glass types, and glass in doors and hazard locations must additionally meet safety glazing requirements.
OBC Division B, Subsection 9.6.1.

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

In practice, manufactured windows certified to NAFS handle this internally: the manufacturer selects glass thickness for the tested size and performance grade. The sizing rules matter most for site-glazed work such as custom fixed picture windows, interior glass partitions, and glass ordered loose from a glass shop. For big feature windows, get the supplier to confirm the glass meets the required design wind pressure for your location and height. Undersized 3 mm glass in a large opening is a real breakage and liability risk.

Plain language

Bigger windows need thicker or tougher glass, and the code has tables tying pane size to glass thickness and wind exposure. Factory-made windows sort this out for you; custom or site-cut glass is where you need to check.

Related questions

Where is safety glass required in a house in Ontario?

Get answers like this for any code question

BUILDAiD Assist searches the building code and answers in plain English with exact citations — in seconds.

Try BUILDAiD Beta

This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.