What R-value does Ontario building code require for a hearth pad under a wood stove on a combustible floor?

The Ontario Building Code does not specify a single R-value requirement for hearth protection under a wood stove — this is a common misconception. The OBC and WETT standards govern hearth pad requirements through clearance-to-combustible rules and physical protection specifications, not thermal resistance ratings expressed as R-values. The relevant standard is CSA B365, the Installation Code for Solid-Fuel-Burning Appliances and Equipment, which WETT inspectors use as their primary reference.

What the code actually requires is that the hearth pad protect the combustible floor from both radiant heat and falling embers. The specific requirements depend on the leg height of your wood stove. A stove with legs providing 150 mm (6 inches) or more of clearance to the floor requires a hearth pad of non-combustible material extending at least 457 mm (18 inches) in front of the door and 203 mm (8 inches) on the remaining sides. A stove with shorter legs — or one sitting directly on the floor — requires a more substantial assembly, typically including an air gap beneath the non-combustible surface to allow heat dissipation.

The practical implication is that your hearth pad needs to be constructed from genuinely non-combustible materials — ceramic tile over cement board, natural stone, brick, or a purpose-built steel hearth pad — rather than simply achieving a certain insulation rating. A layer of tile glued directly over a plywood subfloor, for example, does not meet the standard even though it looks non-combustible on the surface, because the plywood beneath can still char and ignite from sustained radiant heat. The assembly must be non-combustible all the way through, or must incorporate an air gap that keeps temperatures at the combustible floor surface within safe limits.

The most reliable approach is to follow your specific stove manufacturer's installation instructions, which will specify the exact hearth pad construction required for that model — manufacturers engineer these requirements based on the heat output and leg clearance of their particular stove. Those manufacturer specs, combined with CSA B365, are what a WETT inspector will check during their inspection.

This matters enormously for Ottawa homeowners because virtually every home insurer in Ontario requires a WETT inspection before covering a wood stove, and an inadequate hearth pad is one of the most common reasons inspections fail. Getting this right from the start saves you the cost and hassle of tearing out and rebuilding a hearth pad after the fact. If you are planning a wood stove installation and want to make sure the hearth assembly is built correctly the first time, you can browse WETT-certified installers through the Ottawa Construction Network directory at justynrookcontracting.com/directory.