The Ontario Building Code | Clearance to the Fireplace Opening
9.22.9.1. Clearance to the fireplace Opening
(1) Combustible material shall not be placed on or near the face of a fireplace within 150 mm of the fireplace opening, except that where the combustible material projects more than 38 mm out from the face of the fireplace above the opening, such material shall be at least 300 mm above the top of the opening.