The Ontario Building Code | Furring
(1) Except as permitted in Sentences 188.8.131.52.(5) and (6), furring for the attachment of cladding shall be not less than 19 mm by 38 mm lumber when applied over sheathing.
(2) When applied without sheathing, furring referred to in Sentence (1) shall be not less than,
(a) 19 mm by 64 mm lumber on supports spaced not more than 406 mm o.c., or
(b) 19 mm by 89 mm on supports spaced not more than 610 mm o.c.
(3) Furring referred to in Sentence (1) shall be,
(a) securely fastened to the framing, and
(b) spaced not more than 610 mm o.c.