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The British Columbia Building Code | Section 9.4. | Structural Requirements

Division B: Acceptable Solutions Part 9 – Housing and Small Buildings
British Columbia Building Code 2018 Division B
Section 9.4. Structural Requirements
9.4.1. Structural Design Requirements and Application Limitations
9.4.1.1. General
(SeeNoteA-9.4.1.1.)
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 that provided in CWC2014, “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) Part9, or
ii) Part4.
2) Where floor framing is designed in accordance with Clause(1)(b) or(c), and where supporting wall framing
and fastenings, or footings, are designed according to Clause(1)(a), the maximum specified live load on the floor
according to Table4.1.5.3. shall not exceed 2.4kPa.
3) Location-specific information for structural design, including snow and wind loads and seismic spectral
response accelerations, shall be determined according to Subsection1.1.3.
9.4.2. Specified Loads
9.4.2.1. Application
1) This Subsection applies to light-frame constructions 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 12.2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m
2
,
and
f) for flat roofs, there are no significant obstructions on the roof, such as parapet walls, spaced closer than the
distance calculated by
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
= specific weight of snow,kN/m
3
.
(SeeNoteA-9.4.2.1.(1).)
9.4.2.2. Specified Snow Loads
(SeeNoteA-9.4.2.2.)
1) Except as provided in Sentences(2) and(3), specified snow loads shall be not less than those calculated using
the following formula:
D
o
10 (H
o
– 0.8S
s
/)
S C
b
S
s
S
r
Part 9 – Housing and Small Buildings Division B: Acceptable Solutions
Division B
where
S = specified snow load,
C
b
= basic snow load roof factor, which is 0.45 where the entire width of the 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 Subsection1.1.3., and
S
r
= associated 1-in-50-year rain load inkPa, determined according to Subsection1.1.3.
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.
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, whichever is greater, where the platform, or each
segregated area of the platform, serves a single dwelling unit. (SeeNoteA-9.4.2.3.(1).)
9.4.2.4. Attics and Roof Spaces
1) The ceiling joists or truss bottom chords in residential attic or roof spaces having limited accessibility that
precludes the storage of equipment or material 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.
(SeeNoteA-9.4.2.4.(1).)
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).
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
Table 9.4.3.1.
Maximum Deflections
Forming Part of Sentence 9.4.3.1.(1)
Structural Members Typeof Ceiling Supported
Max. Allowable Deflection as an
Expressed Ratio of the
ClearSpan
Roof rafters, roof joists and roof beams No ceiling 1/180
Other than plaster or gypsum
board
1/240
Plaster or gypsum board 1/360
Ceiling joists Other than plaster or
gypsum board
1/240
Plaster or gypsum board 1/360
Floor beams, floor joists and floor decking All cases 1/360
Beams, joists and decking for balconies, decks and other accessible exterior platforms Serving a single dwelling unit 1/240
Other 1/360
Division B: Acceptable Solutions Part 9 – Housing and Small Buildings
British Columbia Building Code 2018 Division B
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.
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 its effects on the building so that the building’s
stability and the performance of assemblies will not be adversely affected. (SeeNoteA-9.4.4.4.(1).)
2) The potential for slope instability and its consequences, such as slope displacement, shall be evaluated based
on site-specific material properties and ground motion parameters referenced in Subsection 1.1.3. and shall be taken
into account in the design of the structure and its foundations.
9.4.4.5. Retaining Walls
1) Walls shall be designed to resist the lateral pressure of the retained material.
9.4.4.6. Walls Supporting Drained Earth
(SeeNoteA-9.4.4.6. and 9.15.1.1.)
Table 9.4.4.1.
Allowable Bearing Pressure for Soil or Rock
Forming Part of Sentence 9.4.4.1.(1)
Typeand Condition of Soil or Rock Maximum Allowable Bearing Pressure, kPa
Dense or compact sand or gravel
(1)
150
Loose sand or gravel
(1)
50
Dense or compact silt
(1)
100
Stiff clay
(1)
150
Firm clay
(1)
75
Soft clay
(1)
40
Till 200
Clay shale 300
Sound rock 500
Notes to Table9.4.4.1.:
(1) See Note A-Table 9.4.4.1.
Part 9 – Housing and Small Buildings Division B: Acceptable Solutions
Division B
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 that has a density of not less than 480kg/m
3
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(1)(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 and effects described in Article4.1.2.1.
Part 9 – Housing and Small Buildings Division B: Acceptable Solutions
Division B
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 that has a density of not less than 480kg/m
3
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(1)(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 and effects described in Article4.1.2.1.