The British Columbia Building Code | Section 4.2. | Foundations
Division B: Acceptable Solutions Part 4 – Structural Design
British Columbia Building Code 2018 Division B
Section 4.2. Foundations
4.2.1. General
4.2.1.1. Application
1) This Section applies to excavations and foundation systems for buildings.
4.2.2. Subsurface Investigations, Drawings and Reviews
4.2.2.1. Subsurface Investigation
1) A subsurface investigation, including groundwater conditions, shall be carried out by or under the direction of a
professional engineer having knowledge and experience in planning and executing such investigations to a degree
appropriate for the building and its use, the ground and the surrounding site conditions. (See NoteA-4.2.2.1.(1).)
4.2.2.2. Drawings
1) Drawings associated with foundations and excavations shall conform to the appropriate requirements of
Section2.2.of DivisionC. (See Article2.2.4.6.of DivisionC.)
4.2.2.3. Field Review
1) A field review shall be carried out by the designer or by another suitably qualified person to ascertain that the
subsurface conditions are consistent with the design and that construction is carried out in accordance with the
design and good engineering practice. (See NoteA-4.2.2.3.(1).)
2) The review required by Sentence(1) shall be carried out
a) on a continuous basis
i) during the construction of all deep foundation units with all pertinent information recorded for each
foundation unit,
ii) during the installation and removal of retaining structures and related backfilling operations, and
iii) during the placement of engineered fills that are to be used to support the foundation units, and
b) as required, unless otherwise directed by the authority having jurisdiction,
i) in the construction of all shallow foundation units, and
ii) in excavating, dewatering and other related works.
4.2.2.4. Altered Subsurface Condition
1) If, during construction, the soil, rock or groundwater is found not to be of the type or in the condition used in
design and as indicated on the drawings, the design shall be reassessed by the designer.
2) If, during construction, climatic or any other conditions change the properties of the soil, rock or groundwater,
the design shall be reassessed by the designer.
4.2.3. Materials Used in Foundations
4.2.3.1. Wood
1) Wood used in foundations or in support of soil or rock shall conform with the appropriate requirements of
Subsection4.3.1.
4.2.3.2. Preservation Treatment of Wood
1) Wood exposed to soil or air above the lowest anticipated groundwater table shall be treated with preservative
in conformance with CAN/CSA-O80 Series, “Wood Preservation,” and the requirements of the appropriate
commodity standard as follows:
a) CAN/CSA-O80.2, “Processing and Treatment,”
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b) CAN/CSA-O80.3, “Preservative Formulations,” or
c) CSAO80.15, “Preservative Treatment of Wood for Building Foundation Systems, Basements, and Crawl
Spaces by Pressure Processes.”
2) Where timber has been treated as required in Sentence(1), it shall be cared for as provided in AWPA M4,
“Care of Preservative-Treated Wood Products,” as revised by Clause6 of CAN/CSA-O80 Series, “Wood
Preservation.”
4.2.3.3. Plain and Reinforced Masonry
1) Plain or reinforced masonry used in foundations or in support of soil or rock shall conform with the
requirements of Subsection4.3.2.
4.2.3.4. Prevention of Deterioration of Masonry
1) Where plain or reinforced masonry in foundations or in structures supporting soil or rock may be subject to
conditions conducive to deterioration, protection shall be provided to prevent such deterioration.
4.2.3.5. Concrete
1) Plain, reinforced or pre-stressed concrete used in foundations or in support of soil or rock shall conform with
the requirements of Subsection4.3.3.
4.2.3.6. Protection Against Chemical Attack
1) Where concrete in foundations may be subject to chemical attack, it shall be treated in conformance with the
requirements in CSAA23.1, “Concrete Materials and Methods of Concrete Construction.”
4.2.3.7. Steel
1) Steel used in foundations or in support of soil or rock shall conform with the appropriate requirements of
Subsection4.3.3. or 4.3.4., unless otherwise specified in this Section.
4.2.3.8. Steel Piles
1) Where steel piles are used in deep foundations and act as permanent load-carrying members, the steel shall
conform with one of the following standards:
a) ASTM A 252, “Welded and Seamless Steel Pipe Piles,”
b) ASTM A 283/A 283M, “Low and Intermediate Tensile Strength Carbon Steel Plates,”
c) ASTM A 1008/A 1008M, “Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy,
High-Strength Low-Alloy with Improved Formability, Solution Hardened, and Bake Hardenable,”
d) ASTM A 1011/A 1011M, “Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High-Strength
Low-Alloy, High-Strength Low-Alloy with Improved Formability, and Ultra-High Strength,” or
e) CSAG40.21, “Structural Quality Steel.”
4.2.3.9. High Strength Steel Tendons
1) Where high strength steel is used for tendons in anchor systems used for the permanent support of a
foundation or in the erection of temporary support of soil or rock adjacent to an excavation, it shall conform with the
requirements of CSAA23.1, “Concrete Materials and Methods of Concrete Construction.”
4.2.3.10. Corrosion of Steel
1) Where conditions are corrosive to steel, adequate protection of exposed steel shall be provided.
(SeeArticle1.2.1.1.of DivisionA for use of other materials.)
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4.2.4. Design Requirements
4.2.4.1. Design Basis
1) The design of foundations, excavations and soil- and rock-retaining structures shall be based on a subsurface
investigation carried out in conformance with the requirements of this Section, and on any of the following, as
appropriate:
a) application of generally accepted geotechnical and civil engineering principles by a professional engineer
especially qualified in this field of work, as provided in this Section and other Sections of Part4,
b) established local practice, where such practice includes successful experience both with soils and rocks of
similar type and condition and with a foundation or excavation of similar type, construction method, size and
depth, or
c) in situ testing of foundation units, such as the load testing of piles, anchors or footings, carried out by a person
competent in this field of work.
(See NoteA-4.2.4.1.(1).)
2) The foundations of a building shall be capable of resisting all the loads stipulated in Section4.1., in accordance
with limit states design in Subsection4.1.3.
3) For the purpose of the application of the load combinations given in Table4.1.3.2.-A, the geotechnical
components of loads and the factored geotechnical resistances at ULS shall be determined by a suitably qualified and
experienced professional engineer. (See NoteA-4.2.4.1.(3).)
4) Geotechnical components of service loads and geotechnical reactions for SLS shall be determined by a
suitably qualified and experienced professional engineer.
5) The foundation of a building shall be designed to satisfy SLS requirements within the limits that the building
is designed to accommodate, including total settlement and differential settlement, heave, lateral movement, tilt or
rotation. (See NoteA-4.2.4.1.(5).)
6) Communication, interaction and coordination between the designer and the professional engineer responsible
for the geotechnical aspects of the project shall take place to a degree commensurate with the complexity and
requirements of the project.
4.2.4.2. Subsurface Investigation
1) A subsurface investigation shall be carried out to the depth and extent to which the building or excavation will
significantly change the stress in the soil or rock
, or to such a depth and extent as to provide all the necessary
information for the design and construction of the excavation or the foundations.
4.2.4.3. Identification
1) The identification and classification of soil, rock and groundwater and descriptions of their engineering and
physical properties shall be in accordance with a widely accepted system.
4.2.4.4. Depth of Foundations
1) Except as permitted in Sentence(2), the bearing surface of a foundation shall be below the level of potential
damage, including damage resulting from frost action, and the foundation shall be designed to prevent damage
resulting from adfreezing and frost jacking. (See NoteA-4.2.4.4.(1).)
2) The bearing surface of a foundation need not be below the level of potential damage from frost where the
foundation
a) is designed against frost action, or
b) overlies material not susceptible to frost action.
4.2.4.5. Sloping Ground
1) Where a foundation is to rest on, in or near sloping ground, this particular condition shall be provided for in
the design.
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4.2.4.6. Eccentric and Inclined Loads
1) Where there is eccentricity or inclination of loading in foundation units, this effect shall be fully investigated
and provided for in the design.
4.2.4.7. Dynamic Loading
1) Where dynamic loading conditions apply, the effects shall be assessed by a special investigation of these
conditions and provided for in the design.
4.2.4.8. Hydrostatic Uplift
1) Where a foundation or any part of a building is subject to hydrostatic uplift, the effects shall be provided for in
the design.
4.2.4.9. Groundwater Level Change
1) Where proposed construction will result in a temporary or permanent change in the groundwater level, the
effects of this change on adjacent buildings shall be fully investigated and provided for in the design.
4.2.4.10. Permafrost
1) Where conditions of permafrost are encountered or proven to exist, the design of the foundation shall be
based upon analysis of these conditions by a person especially qualified in that field of work.
4.2.4.11. Swelling and Shrinking Soils
1) Where swelling or shrinking soils, in which movements resulting from moisture content changes may be
sufficient to cause damage to a structure, are encountered or known to exist, such a condition shall be fully
investigated and provided for in the design.
4.2.4.12. Expanding and Deteriorating Rock
1) Where rock that expands or deteriorates when subjected to unfavourable environmental conditions or to stress
release is known to exist, this condition shall be fully investigated and provided for in the design.
4.2.4.13. Construction on Fill
1) Buildings may be placed on fill if it can be shown by subsurface investigation that
a) the fill is or can be made capable of safely supporting the building,
b) detrimental movement of the building or of services leading to the building will not occur, and
c) explosive gases can be controlled or do not exist.
4.2.4.14. Structural Design
1) The structural design of the foundation of a building, the procedures and construction practices shall conform
with the appropriate Sections of this Code unless otherwise specified in this Section.
4.2.5. Excavations
4.2.5.1. Design of Excavations
1) The design of excavations and of supports for the sides of excavations shall conform with Subsection4.2.4.
and with this Subsection. (See NoteA-4.2.5.1.(1).)
4.2.5.2. Excavation Construction
1) Every excavation shall be undertaken in such a manner as to
a) prevent movement that would cause damage to adjacent buildings at all phases of construction, and
b) comply with the appropriate requirements of Part 8.
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2) Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a
manner that may endanger the integrity of the excavation or its supports.
4.2.5.3. Supported Excavations
1) The sides of an excavation in soil or rock shall be supported by a retaining structure conforming with the
requirements of Articles4.2.5.1. and 4.2.5.2., except as permitted in Article4.2.5.4.
4.2.5.4. Unsupported Excavations
1) The sides of an excavation in soil or rock may be unsupported where a design is prepared in conformance with
the requirements of Articles4.2.5.1. and 4.2.5.2.
4.2.5.5. Control of Water around Excavations
1) Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under
control at all phases of excavation and construction.
4.2.5.6. Loss of Ground
1) At all phases of excavation and construction, loss of ground due to water or any other cause shall be prevented.
4.2.5.7. Protection and Maintenance at Excavations
1) All sides of an excavation, supported and unsupported, shall be continuously maintained and protected from
possible deterioration by construction activity or by the action of frost, rain and wind.
4.2.5.8. Backfilling
1) Where an excavation is backfilled, the backfill shall be placed so as to
a) provide lateral support to the soil adjacent to the excavation, and
b) prevent detrimental movements.
2) The material used as backfill or fill supporting a footing, foundation or a floor on grade shall be of a type that
is not subject to detrimental volume change with changes in moisture content and temperature.
4.2.6. Shallow Foundations
4.2.6.1. Design of Shallow Foundations
1) The design of shallow foundations shall be in conformance with Subsection4.2.4. and the requirements of this
Subsection. (See NoteA-4.2.6.1.(1).)
4.2.6.2. Support of Shallow Foundations
1) Where a shallow foundation is to be placed on soil or rock, the soil or rock shall be cleaned of loose and
unsound material and shall be adequate to support the design load taking into account temperature, precipitation,
construction activities and other factors that may lead to changes in the properties of soil or rock.
4.2.6.3. Incorrect Placement of Shallow Foundations
1) Where a shallow foundation unit has not been placed or located as indicated on the drawings,
a) the error shall be corrected, or
b) the design of the foundation unit shall be recalculated for the altered conditions by the designer and action
taken as required in Article2.2.4.7.of DivisionC.
4.2.6.4. Damaged Shallow Foundations
1) If a shallow foundation unit is damaged,
a) it shall be repaired, or
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b) the design of the foundation unit shall be recalculated for the damaged condition by the designer and action
taken as required in Article2.2.4.7.of DivisionC.
4.2.7. Deep Foundations
4.2.7.1. General
1) A deep foundation shall provide support for a building by transferring loads by end-bearing to a competent
stratum at considerable depth below the structure, or by mobilizing resistance by adhesion or friction, or both, in the
soil or rock in which it is placed. (See NoteA-4.2.7.1.(1).)
4.2.7.2. Design of Deep Foundations
1) Deep foundations shall be designed in conformance with Subsection4.2.4. and this Subsection.
(SeeNoteA-4.2.7.2.(1).)
2) Where deep foundation units are load tested, as required in Clause4.2.4.1.(1)(c), the determination of the
number and type of load test and the interpretation of the results shall be carried out by a professional engineer
especially qualified in this field of work. (See NoteA-4.2.7.2.(2).)
3) The design of deep foundations shall be determined on the basis of geotechnical considerations taking into
account
a) the method of installation,
b) the degree of inspection,
c) the spacing of foundation units and group effects,
d) other requirements in this Subsection, and
e) the appropriate structural requirements in Section4.1. and Subsections4.3.1., 4.3.3. and 4.3.4.
4) The portion of a deep foundation unit permanently in contact with soil or rock shall be structurally designed as
a laterally supported compression member.
5) The portion of a deep foundation unit that is not permanently in contact with soil or rock shall be structurally
designed as a laterally unsupported compression member.
6) The structural design of prefabricated deep foundation units shall allow for all stresses resulting from driving,
handling and testing.
4.2.7.3. Tolerance in Alignment and Location
1) Permissible deviations from the design alignment and the location of the top of deep foundation units shall be
determined by design analysis and shall be indicated on the drawings.
4.2.7.4. Incorrect Alignment and Location
1) Where a deep foundation unit has not been placed within the permissible deviations referred to in
Article4.2.7.3., the condition of the foundation shall be assessed by the designer, any necessary changes made and
action taken as required in Article2.2.4.7.of DivisionC.
4.2.7.5. Installation of Deep Foundations
1) Deep foundation units shall be installed in such a manner as not to impair
a) the strength of the deep foundation units and the properties of the soil or rock on or in which they are placed
beyond the calculated or anticipated limits,
b) the integrity of previously installed
deep foundation units, or
c) the integrity of neighbouring buildings.
4.2.7.6. Damaged Deep Foundation Units
1) Where inspection shows that a deep foundation unit is damaged or not consistent with design or good
engineering practice,
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a) such a unit shall be reassessed by the designer,
b) any necessary changes shall be made, and
c) action shall be taken as required in Article2.2.4.7.of DivisionC.
4.2.8. Special Foundations
4.2.8.1. General
1) Where special foundation systems are used, such systems shall conform to Subsection4.2.4.,
Sentence4.1.1.5.(2) and Article1.2.1.1.of DivisionA.
4.2.8.2. Use of Existing Foundations
1) Existing foundations may be used to support new or altered buildings provided they comply with all pertinent
requirements of this Section.
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a) such a unit shall be reassessed by the designer,
b) any necessary changes shall be made, and
c) action shall be taken as required in Article2.2.4.7.of DivisionC.
4.2.8. Special Foundations
4.2.8.1. General
1) Where special foundation systems are used, such systems shall conform to Subsection4.2.4.,
Sentence4.1.1.5.(2) and Article1.2.1.1.of DivisionA.
4.2.8.2. Use of Existing Foundations
1) Existing foundations may be used to support new or altered buildings provided they comply with all pertinent
requirements of this Section.