9.4.2.

(1) This Subsection applies to light-frame construction whose wall, floor and roof planes are generally comprised of frames of small repetitive structural members, and where,

(a) the roof and wall planes are clad, sheathed or braced on at least one side,

(b) the small repetitive structural members are spaced not more than 600 mm o.c.,

(c) the clear span of any structural member does not exceed 12.20 m,

(d) the maximum deflection of the structural roof members conforms to Article 9.4.3.1.,

(e) the maximum total roof area, notwithstanding any separation of adjoining buildings by firewalls, is 4 550 m², and

(f) for flat roofs, there are no significant obstructions on the roof, such as parapet walls, spaced closer than the distance calculated by,

D_o = 10(H_o – 0.8 S_s/γ)

where,

D_o = minimum distance between obstructions, m,

H_o = height of the obstruction above the roof, m,

S_s = ground snow load, kPa, and

γ = unit weight of snow, kN/m³.

(1) Except as provided in Sentences (2) and (3), specified snow loads shall be not less than those calculated using the following formula:

S = C_b ∙ S_s + S_r

where,

S = specified snow load,

C_b = basic snow load roof factor, which is 0.45 where the entire width of a roof does not exceed 4.3 m and 0.55 for all other roofs,

S_s = 1-in-50 year ground snow load in kPa, determined according to Supplementary Standard SB-1, and

S_r = associated 1-in-50 year rain load in kPa, determined according to Supplementary Standard SB-1.

(2) In no case shall the specified snow load be less than 1 kPa.

(3) Bow string, arch or semi-circular roof trusses having an unsupported span greater than 6 m shall be designed in conformance with the snow load requirements in Subsection 4.1.6.

(1) Balconies, decks and other accessible exterior platforms intended for an occupancy and subject to snow loads shall be designed to carry the specified roof snow load or 1.9 kPa, whichever is greater, where the platform, or each segregated area of the platform, serves a single dwelling unit.

(1) Ceiling joists or truss bottom chords in residential attic or roof spaces shall be designed for a total specified load of not less than 0.35 kPa, where the total specified load is the sum of the specified dead load plus the specified live load of the ceiling and where,

(a) the attic or roof spaces have limited accessibility that precludes the storage of equipment or material, and

(b) the maximum attic height is not more than 1 000 mm measured vertically from the top of the truss bottom chord to the underside of the roof deck.