What are the Ontario Fire Code requirements for chimney clearance from combustible materials during masonry repair?

Chimney clearance from combustibles during masonry repair is governed primarily by the Ontario Fire Code (O. Reg. 213/07) and the Ontario Building Code, with specific clearance requirements that must be maintained — and in many cases restored — when masonry repair work disturbs existing chimney components.

The Core Clearance Requirements

The Ontario Fire Code references the National Building Code of Canada and CSA B365 (Installation Code for Solid-Fuel-Burning Appliances and Equipment) for chimney clearance standards. For masonry chimneys, the fundamental clearances are:

2-inch (50mm) clearance from the exterior face of a masonry chimney to any combustible framing, sheathing, or structural member. This applies to wood framing, OSB, plywood, and any wood-based material. The gap must be maintained continuously from the foundation to above the roofline. When masonry repair work involves repointing, parging, or rebuilding sections of a chimney that passes through a floor assembly or roof, the contractor must verify this clearance is maintained — repair mortar or new masonry must not bridge the gap between the chimney and combustible framing.

1-inch (25mm) clearance is required between the chimney and roof decking or sheathing at the roof penetration. The flashing system must accommodate this gap while remaining weathertight. During chimney repointing or crown repair, disturbing the flashing is common — any flashing work must restore proper clearance and waterproofing simultaneously.

What This Means During Masonry Repair

When a mason is repointing, parging, or rebuilding sections of a chimney, several clearance-related issues commonly arise in GTA homes:

Mortar bridging is the most frequent problem. When repointing chimney joints near a roof penetration or floor assembly, excess mortar can inadvertently fill the required clearance gap between the chimney and combustible framing. This is a fire code violation that is invisible once the wall or ceiling is closed up. Any competent chimney mason should be inspecting these clearances as part of the repair scope.

Flashing disturbance during crown repair or upper chimney repointing can compromise the clearance at the roofline. Step flashing, counter flashing, and base flashing must be reinstalled correctly — both for waterproofing and to maintain the 1-inch clearance between chimney masonry and roof deck. In the GTA, ice damming and freeze-thaw cycling frequently damage chimney flashing, so chimney repair projects should always include flashing inspection and replacement if needed.

Heritage homes in established Toronto neighbourhoods — Rosedale, Cabbagetown, The Annex, Leslieville — often have chimneys that were built before modern clearance requirements existed. Original construction may have zero clearance between the chimney and wood framing. When masonry repair is performed on these chimneys, the Ontario Fire Code requires that the work not worsen the existing condition, and ideally that clearances be brought up to current standards where accessible. A registered chimney sweep or WETT-certified inspector can assess whether existing clearances are acceptable or require remediation.

Permits and Inspections

Chimney masonry repair — repointing, crown repair, parging — generally does not require a building permit in most GTA municipalities when it is cosmetic or maintenance work. However, if the repair involves rebuilding more than 50% of the chimney, altering the flue liner, or changing the chimney height, a permit from the City of Toronto Building Division (or your local municipality) is required, and the work must be inspected to confirm fire code clearances are maintained.

Any chimney connected to a solid-fuel appliance (wood stove, fireplace insert) should be inspected by a WETT (Wood Energy Technology Transfer) certified technician before and after masonry repair. WETT inspection confirms clearances, liner integrity, and fire code compliance — and is typically required by home insurers when a solid-fuel appliance is present.

Practical Guidance

Chimney repointing in the GTA runs $1,000-$5,000 depending on chimney size, height, and scaffolding requirements. Crown repair adds $500-$2,000. Always ask your chimney mason whether they will inspect and document clearances as part of the repair scope — a professional mason should do this automatically. If your chimney connects to any fuel-burning appliance, budget an additional $200-$400 for a WETT inspection after repair is complete.

For chimney work specifically, find experienced masonry contractors through the Toronto Construction Network at torontoconstructionnetwork.com/directory?trade=masonry — and always verify WSIB coverage and liability insurance before work begins at height.