(1) Concealed spaces in interior walls, ceilings, floors and crawl spaces shall be separated by fire blocks from concealed spaces in exterior walls and attic or roof spaces.
(2) Fire blocks shall be provided at all interconnections between concealed vertical and horizontal spaces in interior coved ceilings, drop ceilings and soffits where the exposed construction materials within the concealed spaces have a surface flame-spread rating greater than 25.
(3) Fire blocks shall be provided at the top and bottom of each stair where the stair passes through a floor containing concealed space in which the exposed construction materials within the space have a surface flame-spread rating greater than 25.
(4) Unsprinklered concealed spaces of combustible construction created by a ceiling, roof space or unoccupied attic space shall be separated by fire blocks into,
(a) compartments having no dimension greater than 60 m, if such space contains exposed construction materials having a surface flame-spread rating of 25 or less, and
(b) compartments of not more than 300 m² in area, if such space contains exposed construction materials having a surface flame-spread rating greater than 25.
(5) No dimension of the compartment described in Clause (4) (b) shall exceed 20 m.
(6) Concealed spaces in mansard or gambrel style roofs, exterior cornices, balconies and canopies of combustible construction in which the exposed construction materials within the space have a surface flame-spread rating exceeding 25 shall have vertical fire blocks at intervals of not more than 20 m and at points where such concealed spaces extend across the ends of required vertical fire separations.