Section 9.4. Structural Requirements

9.4.1. Structural Design Requirements and Application Limitations

9.4.1.1. General (See Appendix A.)

(1) Subject to the application limitations defined elsewhere in this Part, structural members and their connections shall,
(a) conform to requirements provided elsewhere in this Part,
(b) be designed according to good engineering practice such as provided in the CWC, "Engineering Guide for Wood Frame Construction", or
(c) be designed according to Part 4 using the loads and deflection and vibration limits specified in,
(i) this Part, or
(ii) Part 4.

(2) Where floor framing is designed in accordance with Clause (l)(b) or (c) and where supporting wall framing and fastenings, or footings are designed according to Clause (l)(a), the specified live load on the floor shall not exceed 2.4kPa (50psf).

(3) Location-specific information for structural design, including snow and wind loads and seismic spectral response accelerations, shall be determined according to Supplementary Standard SB-1. (See Appendix A.)

9.4.2. Specified Loads

9.4.2.1. Application (See Appendix A.)

9.4.2.1. Application (See Appendix A.)
(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 (23% in) o.c.,
(c) the clear span of any structural member does not exceed 12.20 m (40 ft),
(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 (49 000 ft2), and
(f) for flat roofs, there

D0 = 10(H0 - 0.8 Ss/Y)

where,
D0 = minimum distance between obstructions, m,
H0 = height of the obstruction above the roof, m,
Ss = ground snow load, kPa, and
Y = unit weight of snow, kN/m3.

9.4.2.2. Specified Design Snow Loads

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

s = cb • ss + sr

where,
S = specified snow load,
Cb = basic snow load roof factor, which is 0.45 where the entire width of a roof does not exceed 4.3 m (14 ft 1 in) and 0.55 for all other roofs,
Ss = l-in-50 year ground snow load in kPa, determined according to Supplementary Standard SB-1, and
Sr = associated l-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 (20 psf).
(3) Bow string, arch or semi-circular roof trusses having an unsupported span greater than 6 m (19 ft 8 in) shall be designed in conformance with the snow load requirements in Subsection 4.1.6.

9.4.2.3. Platforms Subject to Snow and Occupancy Loads

(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 (40 psf), whichever is greater, where the platform, or each segregated area of the platform, serves a single dwelling unit. (See Appendix A.)

9.4.2.4. Attics and Roof Spaces

(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 (7 psf), 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 (3 ft 3 in) measured vertically from the top of the truss bottom chord to the underside of the roof deck. (See Appendix A.)

9.4.3. Deflections

9.4.3.1. Deflections

(1) The maximum deflection of structural members shall conform to Table 9.4.3.1.
(2) Dead loads need not be considered in computing deflections referred to in Sentence (1).

Table 9.4.3.1.
Maximum Deflections
Forming Part of Sentence 9.4.3.1 .(1)

9.4.4. Foundation Conditions

9.4.4.1. Allowable Bearing Pressures

(1) Footing sizes for shallow foundations shall be,
(a) determined in accordance with Section 9. 15. , or
(b) designed in accordance with Section 4.2. using,
(i) the maximum allowable bearing pressures in Table 9.4.4. 1 ., or
(ii) allowable bearing pressures determined from subsurface investigation.

Table 9.4.4.1.
Allowable Bearing Pressure for Soil or Rock
Forming Part of Sentence 9.4.4.1 .(1 )

(2) The design procedures described in Section 4.2. are permitted to be used in lieu of the design procedures in this Subsection.
(3) The design procedures described in Section 4.2. shall be used where,
(a) deep foundations are used,
(b) the footing size falls outside the scope of this Section, or
(c) the foundation is constructed on peat, filled ground or on sensitive clays as described in Article 9.15.1.1.

9.4.4.2. Foundation Capacity in Weaker Soil and Rock

(1) Where a soil or rock within a distance equal to twice the footing width below the bearing surface has a lower allowable bearing pressure than that at the bearing surface as shown in Article 9.4.4.1., the design capacity of the foundation shall not be greater than would cause the weakest soil or rock to be stressed beyond its allowable bearing pressure.
(2) In calculating subsurface pressures referred to in Sentence (1), the loads from the footings shall be assumed to be distributed uniformly over a horizontal plane within a frustum extending downward from the footing at an angle of 60° to the horizontal.

9.4.4.3. High Water Table

(1) Where a foundation bears on gravel, sand or silt, and the water table is within a distance below the bearing surface equal to the width of the foundation, the allowable bearing pressure shall be 50% of that determined in Article 9.4.4.1.

9.4.4.4. Soil Movement

(1) Where a foundation is located in an area where soil movement caused by changes in soil moisture content, freezing, or chemical-microbiological oxidation is known to occur to the extent that it will damage a building, measures shall be taken to preclude such movement or to reduce the effects on the building so that the building's stability and the performance of assemblies will not be adversely affected. (See Appendix A.)
(2) Any surcharge shall be in addition to the equivalent fluid pressure specified in Sentence (1).

9.4.4.5. Reserved

Reserved

9.4.4.6. Wall Supporting Drained Earth (See Appendix A.)

(1) Except where constructed in accordance with Section 9.15., walls supporting drained earth shall be designed,
(a) for a pressure equivalent to that exerted by a fluid with a density of not less than 480 kg/m3 (30 lb/ft3) and a depth equal to that of the retained earth, or
(b) in accordance with Section 4.2. so as to be able to resist the loads and effects described in Article 4.1.2.1.
(2) Walls supporting other than drained earth shall be designed,
(a) for the pressure described in Clause l(a) plus the fluid pressure of the surcharge, or
(b) in accordance with Section 4.2. so as to be able to resist the loads, forces and effects described in Article 4.1.2.1.