← Ontario Building Code FAQ
OBC DIVISION B · PART 9 · SECTION 9.22 — FIREPLACES

How big does a fireplace hearth extension need to be in Ontario?

A masonry fireplace hearth must extend at least 400 mm (16 in.) in front of the fireplace opening and at least 200 mm (8 in.) beyond each side of the opening, built of noncombustible material and properly supported, so embers land on protection rather than flooring.

Code reference
Fireplaces must have a noncombustible hearth extending in front of and beside the fire chamber opening, with the minimum projection in front of the opening set at 400 mm and the minimum side extension at 200 mm beyond each side. The hearth must be supported by noncombustible construction and detailed so combustible framing is not exposed beneath it.
OBC Division B, Subsection 9.22.5.

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

What this means in practice

The hearth extension is spark and ember protection, so it is measured from the finished opening, not the firebox back. Raised fireplaces and factory-built units may have their own listed requirements, but for site-built masonry the 400/200 mm figures govern. Watch support details: cantilevered or reinforced hearth slabs must not bear on combustible formwork left in place, and hardwood or laminate flooring must stop clear of the hearth rather than tuck under it. Renovations that reface a fireplace and shrink the surround sometimes accidentally reduce the effective hearth dimensions below minimum.

Plain language

The fireproof pad in front of your fireplace must reach at least 400 mm out into the room and 200 mm past each side of the opening. Its job is simple: when a log pops and throws an ember, it should land on stone or tile, not on your floor.

Related questions

What clearances and damper requirements apply to fireplaces 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.