How is guard height measured on Ontario deck stairs?

On deck stairs in Ontario, guard height is measured vertically from the top of the guard down to an imaginary line drawn through the nosings of the treads below. That line, not the stringer or the tread surface directly beneath the guard post, is the reference point.

The 2024 Ontario Building Code sets the minimum guard height at 900 mm for exterior guards serving not more than one dwelling unit, where the walking surface served is not more than 1 800 mm above finished ground level. That 900 mm minimum applies to the stair guard as well, measured the way described above. If the deck surface itself is more than 1 800 mm above grade, the guard on the landing must be at least 1 070 mm, and guards on exterior stairs or landings more than 10 m above adjacent ground must be at least 1 500 mm.

A few other Code rules matter just as much as the height:

• Openings through the guard must prevent the passage of a 100 mm sphere. On a stair guard specifically, the triangle formed by the riser, the tread and the bottom rail must also prevent the passage of a 150 mm sphere.
• The Code requires that no member, attachment or opening between 140 mm and 900 mm above the walking surface facilitates climbing. This is an Ontario-specific rule that applies to every required guard, including stair guards. Horizontal rails or cable infill running between those heights can facilitate climbing, which is what this rule targets.

The measurement method matters on a sloping stair: measure vertically from the nosing line, not from the tread directly under a post, and put the guard height in the drawings and the quote.

If your stair guard is part of a manufactured or pre-engineered system, glass panels for example, the City of Ottawa asks for the manufacturer's information and attachment details with the permit application. The Code's height and opening rules above still apply to it.

If your deck's walking surface is more than 600 mm (24 in.) above adjacent grade, or if the deck is raised and is the main way into the house, the City of Ottawa requires a building permit. The City's framing inspection is at completion of structural framing and guards, and the final inspection at completion of the deck framing, stairs and guards.