Excavation, dampproofing, drainage, footings and foundations (House)

Last updated October 22, 2026

Values this chapter turns on

added footing width per storey of veneer: 65 mm; added footing width per storey of veneer
min foundation depth, clay soils: 1.2 m; min foundation depth, clay soils
min polyethylene dampproofing under a slab: 0.15 mm; min polyethylene dampproofing under a slab
min concrete slab thickness, floors-on-ground: 75 mm; min concrete slab thickness, floors-on-ground

This chapter covers everything below the first floor: excavation, keeping water and soil gas out, drainage, footings, foundation walls and the basement slab. Sections 9.12 to 9.16 are short and full of small numbers. Expect direct lookups and a table question on footing widths or wall thickness.

Excavation, foundation depth and backfill (9.12)

Remove topsoil under the building, and keep the excavation bottom free of organic material, standing water and frost. In areas with termites, stumps and roots come out to at least 300 mm below unexcavated areas OBC Div. B 9.12.1.1.. Footings must go down to undisturbed soil OBC Div. B 9.12.2.1..

Minimum foundation depth comes from Table 9.12.2.2.. Read it with three inputs: soil type, whether the foundation contains heated space, and whether the soil drains well.

Soil	Heated basement, good drainage	No heated space, poor drainage
Rock	no limit	no limit
Coarse grained	no limit	below frost penetration
Clay or not clearly defined	1.2 m	1.2 m, and not less than frost depth

A foundation insulated so it cuts heat flow to the soil under the footings is treated as having no heated space OBC Div. B 9.12.2.2.(2). Steps with 1 or 2 risers can sit on the ground. The table depths do not apply to small accessory buildings (not masonry, 1 storey, not more than 55 m², and not more than 600 mm from ground to the underside of the joists) or to similar low decks that carry no roof and are not attached to another structure, unless differential movement is shown to be harmless.

Backfill within 600 mm of the foundation must be free of deleterious debris and of boulders larger than 250 mm diameter. Grade it so water drains away after settling, and brace the wall before backfilling if it needs lateral support or the concrete has not reached strength OBC Div. B 9.12.3.3., 9.12.3.4..

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Dampproofing, waterproofing and soil gas (9.13)

Dampproofing is the normal case: it applies where drainage per Section 9.14 is provided. Waterproofing is needed only where there is hydrostatic pressure, and for roofs of underground structures OBC Div. B 9.13.3.1..

Foundation walls are dampproofed on the outside, from finished ground level down to the top of the footing, wherever outside grade is higher than the inside floor. Waterproofing replaces it OBC Div. B 9.13.2.1., 9.13.2.4..
Masonry block walls get at least 6 mm of mortar parging, coved over the footing, before dampproofing.
Floors-on-ground are dampproofed, except garage floors, floors in unenclosed parts of a building, and floors over granular fill that meets 9.16.2.1.
Below a slab, dampproofing can be polyethylene at least 0.15 mm thick with 100 mm laps, Type S roll roofing, or suitable rigid polystyrene. Between a slab and a finished floor, 0.05 mm polyethylene is enough OBC Div. B 9.13.2.6..
A waterproofed basement floor is a membrane sandwiched between two concrete layers, each at least 75 mm OBC Div. B 9.13.3.5..

Soil gas: every wall, roof and floor in contact with the ground must resist soil gas leakage per Subsection 9.25.3 or SB-9 (garages and unenclosed spaces excepted). Houses also need a radon rough-in OBC Div. B 9.13.4.2.. The pipe option is a pipe of at least 100 mm diameter through the slab, opening into the granular layer near the centre of the floor, with an airtight cap and a label near the cap, every 1.8 m and at each change of direction OBC Div. B 9.13.4.3..

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Foundation and surface drainage (9.14)

Provide drainage at the bottom of every foundation wall that encloses interior space, unless shown unnecessary. Where exterior insulation goes deeper than 900 mm below grade, you also need a drainage layer, such as 19 mm mineral fibre or 100 mm of free-draining granular material OBC Div. B 9.14.2.1..

Item	Minimum
Drain tile or pipe diameter	100 mm
Stone cover over top and sides of tile	150 mm
Granular drainage layer under footing	125 mm deep, 300 mm past the footing
Sump pit	750 mm deep, 0.25 m², with a cover
Dry well distance from foundation	5 m

Sources: 9.14.3.2., 9.14.3.3., 9.14.4.2., 9.14.5.2., 9.14.5.3.. Sump covers resist removal by children and are airtight. Dry wells are allowed only where groundwater is below their bottom.

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Footings (9.15.1 to 9.15.3)

Section 9.15 applies to footings on stable soil with an allowable bearing pressure of at least 75 kPa. On fill, peat or sensitive clay the footings must be designed under Section 4.2. Sensitive clay means most particles are smaller than 0.002 mm, which includes leda clay OBC Div. B 9.15.1.1.. The table sizes also assume joist spans of not more than 4.9 m and floor live loads of not more than 2.4 kPa OBC Div. B 9.15.3.3..

Basic sizes from Table 9.15.3.4., for light wood-frame construction:

Floors supported	Exterior wall strip	Interior wall strip	Column pad (3 m spacing)
1	250 mm	200 mm	0.40 m²
2	350 mm	350 mm	0.75 m²

Then adjust. Exterior strip footings grow by 65 mm for each storey of masonry veneer, 130 mm for each storey of solid masonry, and 150 mm for each storey of flat ICF wall OBC Div. B 9.15.3.5.. Column pads scale with column spacing. Double the widths and areas where the water table in gravel, sand or silt is closer than one footing width below the bearing surface.

Footing thickness is the greater of 100 mm or the projection beyond the wall it supports OBC Div. B 9.15.3.8.. A 200 mm wall centred on a 500 mm footing projects 150 mm each side, so the footing must be at least 150 mm thick. Step footings: rise not more than 600 mm, run not less than 600 mm.

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Foundation walls (9.15.4 to 9.15.6)

Unreinforced concrete, block and flat ICF wall thickness comes from Table 9.15.4.2.-A. Read it by material block (15 MPa concrete, 20 MPa concrete, unreinforced block), then thickness, then whether the wall is laterally supported at the top and how tall it is. The value is the maximum height of finished ground above the basement floor. For example, a 190 mm unreinforced block wall that is supported at the top and not more than 2.5 m high can retain up to 1.2 m of fill. The same wall unsupported at the top is limited to 0.9 m.

A wall counts as supported at the top when the floor is anchored to it with anchor bolts, the joists are embedded in it, or it carries solid masonry OBC Div. B 9.15.4.3.. Openings wider than 1.2 m, or totalling more than 25% of the wall length, make the wall below them unsupported unless reinforced.

Other numbers worth flagging:

Exterior foundation walls extend at least 150 mm above finished ground OBC Div. B 9.15.4.6..
A wall reduced in thickness at the top for joists: not more than 350 mm high and not less than 90 mm thick.
Crack control joints in walls longer than 25 m, at not more than 15 m spacing.
Hollow block walls under joists are capped with 50 mm of concrete or solid units, unless the three termite and plate exceptions all apply. At least 190 mm of solid masonry goes under beams OBC Div. B 9.15.5.2..
Pilasters are needed under beams framing into block walls 140 mm thick or less.

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Floors-on-ground (9.16)

Place at least 100 mm of coarse clean granular fill (not more than 10% passing a 4 mm sieve) under floors-on-ground, except in garages, carports and accessory buildings OBC Div. B 9.16.2.1.. Concrete slabs are at least 75 mm thick, not counting any topping. A topping, if used, is at least 20 mm. Put a bond break between the slab and footings or rock, and do not dust dry cement on the surface OBC Div. B 9.16.4.3.. A slab that carries loads from the superstructure is designed under Part 4.

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Common traps

Mixing up the heated and unheated columns of Table 9.12.2.2.
Using 0.10 mm or 0.05 mm polyethylene where 0.15 mm under a slab is required.
Forgetting the veneer add-on to footing width, or using 130 mm (solid masonry) for veneer.
Reading the unsupported column of Table 9.15.4.2.-A when the floor is bolted to the wall.

Chapter review

Chapter at a glance

One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.

Chapter at a glance: the key idea in each section
Section	Key idea
Excavation, foundation depth and backfill (9.12)	Remove topsoil under the building, and keep the excavation bottom free of organic material, standing water and frost.
Dampproofing, waterproofing and soil gas (9.13)	Dampproofing is the normal case: it applies where drainage per Section 9.14 is provided.
Foundation and surface drainage (9.14)	Provide drainage at the bottom of every foundation wall that encloses interior space, unless shown unnecessary.
Footings (9.15.1 to 9.15.3)	Section 9.15 applies to footings on stable soil with an allowable bearing pressure of at least 75 kPa.
Foundation walls (9.15.4 to 9.15.6)	A wall counts as supported at the top when the floor is anchored to it with anchor bolts, the joists are embedded in it, or it carries solid masonry.
Floors-on-ground (9.16)	Place at least 100 mm of coarse clean granular fill (not more than 10% passing a 4 mm sieve) under floors-on-ground, except in garages, carports and accessory buildings.

Excavation, foundation depth and backfill (9.12)
Remove topsoil under the building, and keep the excavation bottom free of organic material, standing water and frost.
Dampproofing, waterproofing and soil gas (9.13)
Dampproofing is the normal case: it applies where drainage per Section 9.14 is provided.
Foundation and surface drainage (9.14)
Provide drainage at the bottom of every foundation wall that encloses interior space, unless shown unnecessary.
Footings (9.15.1 to 9.15.3)
Section 9.15 applies to footings on stable soil with an allowable bearing pressure of at least 75 kPa.
Foundation walls (9.15.4 to 9.15.6)
A wall counts as supported at the top when the floor is anchored to it with anchor bolts, the joists are embedded in it, or it carries solid masonry.
Floors-on-ground (9.16)
Place at least 100 mm of coarse clean granular fill (not more than 10% passing a 4 mm sieve) under floors-on-ground, except in garages, carports and accessory buildings.

Usual exam traps

Mixing up the heated and unheated columns of Table 9.12.2.2.
Using 0.10 mm or 0.05 mm polyethylene where 0.15 mm under a slab is required.
Forgetting the veneer add-on to footing width, or using 130 mm (solid masonry) for veneer.
Reading the unsupported column of Table 9.15.4.2.-A when the floor is bolted to the wall.

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Questions on Excavation, dampproofing, drainage, footings and foundations, in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.

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Code cited in this chapter

Based on the official 2024 Building Code Compendium on ontario.ca.

OBC Div. B 9.12.1.1. Removal of Topsoil and Organic Matter
(1)The topsoil and vegetable matter in all unexcavated areas under a building shall be removed.
(2)In localities where termite infestation is known to be a problem, all stumps, roots and other wood debris shall be removed from the soil to a depth of not less than 300 mm in unexcavated areas under a building.
(3)The bottom of every excavation shall be free of all organic material.
Open OBC Div. B 9.12.1.1. in the code viewer
OBC Div. B 9.12.2.1. Excavation to Undisturbed Soil
(1)Excavations for foundations shall extend to undisturbed soil.
Open OBC Div. B 9.12.2.1. in the code viewer
OBC Div. B Table 9.12.2.2. Minimum Depths of Foundations — Forming Part of Sentence 9.12.2.2.(1)
Table 9.12.2.2 — Minimum Depths of Foundations — Forming Part of Sentence 9.12.2.2.(1) Forming Part of Sentence 9.12.2.2.(1) Type of Soil | Min Depth of Foundation Containing Heated Basement or Crawl Space[1] With Good Soil Drainage | Min Depth of Foundation Containing Heated Basement or Crawl Space[1] With Poor Soil Drainage | Min Depth of Foundation Containing No Heated Space[2] With Good Soil Drainage | Min Depth of Foundation Containing No Heated Space[2] With Poor Soil Drainage Rock | No limit | No limit | No limit | No limit Coarse grained soils | No limit | No limit | No limit | Below the depth of frost penetration Silt | No limit | No limit | Below the depth of frost penetration | Below the depth of frost penetration Clay or soils not clearly defined[4] | 1.2 m[3] | 1.2 m | 1.2 m but not less than the depth of frost penetration[3] | 1.2 m but not less than the depth of frost penetration Notes to Table 9.12.2.2.: (1) Foundation not insulated to reduce heat loss through the footings. (2) Including foundations insulated to reduce heat loss through the footings. (3) Good soil drainage to not less than the depth of frost penetration. (4) See Note A-Table 9.12.2.2.
Open OBC Div. B Table 9.12.2.2. in the code viewer
OBC Div. B 9.12.2.2. Minimum Depth of Foundations
(1)Except as provided in Sentences (4) to (7), the minimum depth of foundations below finished ground level shall conform to Table 9.12.2.2.
(2)Where a foundation is insulated in a manner that will reduce the heat flow to the soil beneath the footings, the foundation depth shall conform to that required for foundations containing no heated space. (See Note A-9.12.2.2.(2))
(3)The minimum depth of foundations for exterior concrete steps with more than 2 risers shall conform to Sentences (1), (2) and (5).
(4)Concrete steps with 1 and 2 risers are permitted to be laid on ground level.
(5)The foundation depths required in Sentence (1) are permitted to be decreased where experience with local soil conditions shows that lesser depths are satisfactory, or where the foundation is designed for lesser depths.
(6)The foundation depths required in Sentence (1) do not apply to foundations for
(a)buildings
(i)that are not of masonry or masonry veneer construction, and
(ii)whose superstructure conforms with the requirements of the deformation resistance test in CSA Z240.2.1, "Structural requirements for manufactured homes," or
(b)accessory buildings
(i)that are not of masonry or masonry veneer construction,
(ii)not more than 1 storey in building height,
(iii)not more than 55 m² in building area, and
(iv)where the distance from finished ground to the underside of the floor joists is not more than 600 mm.
(7)The foundation depths required by Sentence (1) do not apply to foundations for decks and other accessible exterior platforms
(a)of not more than 1 storey,
(b)not more than 55 m² in area,
(c)where the distance from finished ground to the underside of the floor joists is not more than 600 mm,
(d)not supporting a roof, and
(e)not attached to another structure, unless it can be demonstrated that differential movement will not adversely affect the performance of that structure.
Open OBC Div. B 9.12.2.2. in the code viewer
OBC Div. B 9.12.3.3. Deleterious Debris and Boulders
(1)Backfill that is within 600 mm of the foundation shall be free of deleterious debris and boulders larger than 250 mm diam. (See Note A-9.12.3.3.(1))
(2)Except as permitted in Sentence (3), backfill shall not contain pyritic material or material that is susceptible to ice lensing in concentrations that will damage the building to a degree that would adversely affect its stability or the performance of assemblies separating dissimilar environments. (See Note A-9.4.4.4.(1))
(3)Backfill with material of any concentration that is susceptible to ice lensing is permitted where foundation walls are
(a)cast-in-place concrete,
(b)concrete block insulated on the exterior, or
(c)concrete block protected from the backfill by a material that serves as a slip plane.
(See Note A-9.4.4.4.(1))
Open OBC Div. B 9.12.3.3. in the code viewer
OBC Div. B 9.12.3.4. Lateral Support of Foundation Wall
(1)Where the height of foundation wall is such that lateral support is required, or where the required concrete strength of the wall has not been reached, the wall shall be braced or laterally supported before backfilling.
Open OBC Div. B 9.12.3.4. in the code viewer
OBC Div. B 9.13.3.1. Required Waterproofing
(1)Where hydrostatic pressure occurs, waterproofing is required for assemblies separating interior space from the ground to prevent the ingress of water into building assemblies and interior spaces.
(2)Waterproofing is required for roofs of underground structures to prevent the ingress of water into building assemblies and interior spaces.
Open OBC Div. B 9.13.3.1. in the code viewer
OBC Div. B 9.13.2.1. Required Dampproofing
(1)Except as provided in Sentence (4) and Article 9.13.3.1., where the exterior finished ground level is at a higher elevation than the ground level inside the foundation walls, exterior surfaces of foundation walls below ground level shall be dampproofed.
(2)Except as provided in Sentence (3) and Article 9.13.3.1., floors-on-ground shall be dampproofed.
(3)Floors in garages, floors in unenclosed portions of buildings and floors installed over granular fill in conformance with Article 9.16.2.1. need not be dampproofed.
(4)Dampproofing in Sentence (1) is not required where the exterior surfaces of foundation walls below ground level are waterproofed.
Open OBC Div. B 9.13.2.1. in the code viewer

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OBC Div. B 9.13.2.4. Application of Dampproofing Material
(1)Exterior dampproofing shall be applied from finished ground level to the top of the exterior of the footing.
(2)Unless otherwise stated in this Subsection, dampproofing shall be installed in accordance with the manufacturer's instructions with regard to
(a)surface priming,
(b)conditions during application,
(c)application quantity and rate, and
(d)curing times.
(3)Joints, cracks and penetrations shall be sealed to maintain the continuity of the dampproofing, where the dampproofing material is not capable of bridging such discontinuities.
Open OBC Div. B 9.13.2.4. in the code viewer
OBC Div. B 9.13.2.6. Dampproofing of Floors-on-Ground
(1)Where dampproofing is installed below the floor, it shall consist of
(a)polyethylene not less than 0.15 mm thick with joints lapped not less than 100 mm,
(b)Type S roll roofing with joints lapped not less than 100 mm, or
(c)rigid extruded/expanded polystyrene with sealed or shiplapped joints that has
(i)sufficient compressive strength to support the floor assembly, and
(ii)a water vapour permeance complying with Clause 9.13.2.2.(2)(a). (See Note A-9.13.2.6.(1))
(2)Where dampproofing is installed between a floor-on-ground and a finished floor, it shall consist of
(a)rigid extruded/expanded polystyrene with sealed or shiplapped joints that has
(i)sufficient compressive strength to support the floor assembly, and
(ii)a water vapour permeance complying with Clause 9.13.2.2.(2)(b), or
(b)polyethylene not less than 0.05 mm thick with joints lapped not less than 100 mm.
Open OBC Div. B 9.13.2.6. in the code viewer
OBC Div. B 9.13.3.5. Floor Waterproofing System
(1)Basement floors-on-ground to be waterproofed shall have a system of membrane waterproofing provided between 2 layers of concrete, each of which shall be not less than 75 mm thick, with the floor membrane made continuous with the wall membrane to form a complete seal.
Open OBC Div. B 9.13.3.5. in the code viewer
OBC Div. B 9.13.4.2. Protection from Soil Gas Ingress
(1)Except as provided in Sentence (1.1), all wall, roof and floor assemblies in contact with the ground shall be constructed to resist the leakage of soil gas from the ground into the building in accordance with Subsection 9.25.3. or MMAH Supplementary Standard SB-9, "Requirements for Soil Gas Control."
(1.1)Construction to resist leakage of soil gas into the building is not required for garages and unenclosed portions of buildings.
(1.2)Where polyethylene is used to provide a barrier to soil gas ingress through floors-on-ground, it shall conform to CAN/CGSB-51.34-M, "Vapour Barrier, Polyethylene Sheet, for Use in Building Construction."
(2)Unless the space between the air barrier system and the ground is designed to be accessible for the future installation of a subfloor depressurization system, dwelling units and buildings containing residential occupancies shall be provided with the rough-in for a radon extraction system conforming to Article 9.13.4.3.
(3)Where buildings are used for occupancies other than those described in Sentence (2), protection from radon ingress and the means to address high radon concentrations in the future shall conform to
(a)Article 9.13.4.3., or
(b)Parts 5 and 6. (See Article 5.4.1.1. and 6.2.1.1.) (See Note A-9.13.4.2.(3))
Open OBC Div. B 9.13.4.2. in the code viewer
OBC Div. B 9.13.4.3. Providing for the Rough-in for a Subfloor Depressurization System
(1)Floors-on-ground shall be provided with a rough-in for subfloor depressurization consisting of
(a)a gas-permeable layer, an inlet and an outlet as described in Sentence (2), or
(b)clean granular material and a pipe as described in Sentence (3).
(2)The rough-in referred to in Clause (1)(a) shall include
(a)a gas-permeable layer installed in the space between the air barrier and the ground to allow the depressurization of that space,
(b)an inlet that allows for the effective depressurization of the gas-permeable layer, and (See Note A-9.13.4.3.(2) (b) and (3)(b)(i))
(c)an outlet in the conditioned space that
(i)permits connection to depressurization equipment,
(ii)is sealed to maintain the integrity of the air barrier system, and
(iii)is clearly labeled to indicate that it is intended only for the removal of radon from below the floor-on-ground.
(3)The rough-in referred to in Clause (1)(b) shall include
(a)clean granular material installed below the floor-on-ground in accordance with Sentence 9.16.2.1.(1), and
(b)pipe not less than 100 mm in diameter installed through the floor, such that
(i)its bottom end opens into the granular layer required in Clause (a) at or near the centre of the floor and not less than 100 mm of granular material projects beyond the terminus of the pipe measured along its axis, (See Note A-9.13.4.3.(2) (b) and (3)(b)(i))
(ii)its top end permits connection to depressurization equipment and is provided with an airtight cap, and
(iii)the pipe is clearly labeled near the cap and, if applicable, every 1.8 m and at every change in direction to indicate that it is intended only for the removal of radon from below the floor-on-ground.
Open OBC Div. B 9.13.4.3. in the code viewer
OBC Div. B 9.14.2.1. Foundation Wall Drainage
(1)Unless it can be shown to be unnecessary, drainage shall be provided at the bottom of every foundation wall that contains the building interior.
(1.1)Except as provided in Sentences (3) and (4), where the insulation on a foundation wall extends to more than 900 mm below the adjacent exterior ground level
(a)a drainage layer shall be installed adjacent to the exterior surface of a foundation wall consisting of
(i)not less than 19 mm mineral fibre insulation with a density of not less than 57 kg/m³, or
(ii)not less than 100 mm of free draining granular material, or
(b)a system shall be installed that can be shown to provide equivalent performance to that provided by the materials described in Clause (a). ( See Note A-9.14.2.1.(1.1) )
(2)Where mineral fibre insulation, crushed rock backfill or other drainage layer medium is provided adjacent to the exterior surface of a foundation wall,
(a)the insulation, backfill or other drainage layer medium shall extend to the footing level to facilitate drainage of ground water to the foundation drainage system, and ( See Note A-9.14.2.1.(1.1) )
(b)any pyritic material in the crushed rock shall be limited to a concentration that will not damage the building to a degree that would adversely affect its stability or the performance of assemblies separating dissimilar environments. (See Note A-9.4.4.4.(1)) (See Sentence 9.12.3.3.(2))
(3)Except when the insulation provides the drainage layer required in Clause (2)(a), when exterior insulation is provided, the drainage layer shall be installed on the exterior face of the insulation.
(4)The drainage layer required in Sentence (2) is not required
(a)when the foundation wall is not required to be dampproofed, or
(b)when the foundation wall is waterproofed.
(5)Where drainage is required in Sentence (1), the drainage shall conform to Subsection 9.14.3. or 9.14.4.
Open OBC Div. B 9.14.2.1. in the code viewer
OBC Div. B 9.14.3.2. Minimum Size
(1)Drain tile or pipe used for foundation drainage shall be not less than 100 mm in diam.
Open OBC Div. B 9.14.3.2. in the code viewer
OBC Div. B 9.14.3.3. Installation
(1)Drain tile or pipe shall be laid on undisturbed or well-compacted soil so that the top of the tile or pipe is below the bottom of the floor slab or the ground cover of the crawl space.
(2)Drain tile or pipe with but joints shall be laid with 6 mm to 10 mm open joints.
(3)The top half of joints referred to in Sentence (2) shall be covered with sheathing paper, 0.10 mm polyethylene or No. 15 asphalt or tar-saturated felt.
(4)The top and sides of drain pipe or tile shall be covered with not less than 150 mm of crushed stone or other coarse clean granular material containing not more than 10% of material that will pass a 4 mm sieve.
Open OBC Div. B 9.14.3.3. in the code viewer
OBC Div. B 9.14.4.2. Installation
(1)Granular material described in Article 9.14.4.1. shall be laid on undisturbed or compacted soil to a minimum depth of not less than 125 mm beneath the footing of the building and extend not less than 300 mm beyond the outside edge of the footings.
Open OBC Div. B 9.14.4.2. in the code viewer
OBC Div. B 9.14.5.2. Sump Pits
(1)Where a sump pit is provided it shall be
(a)not less than 750 mm deep,
(b)not less than 0.25 m² in area, and
(c)provided with a cover.
(2)Covers for sump pits shall be designed
(a)to resist removal by children, and
(b)to be airtight in accordance with Sentence 9.25.3.3.(7)
(3)Where gravity drainage is not practical, an automatic sump pump shall be provided to discharge the water from the sump pit described in Sentence (1) into a sewer, drainage ditch or dry well.
Open OBC Div. B 9.14.5.2. in the code viewer
OBC Div. B 9.14.5.3. Dry Wells
(1)Dry wells may be used only when located in areas where the natural groundwater level is below the bottom of the dry well.
(2)Dry wells shall be not less than 5 m from the building foundation and located so that drainage is away from the building.
Open OBC Div. B 9.14.5.3. in the code viewer
OBC Div. B 9.15.1.1. General
(1)Except as provided in Articles 9.15.1.2. and 9.15.1.3., this Section applies to
(a)concrete or unit masonry foundation walls and concrete footings not subject to surcharge
(i)on stable soils with an allowable bearing pressure of 75 kPa or greater, and
(ii)for buildings of wood-frame or masonry construction,
(b)wood-frame foundation walls and wood or concrete footings not subject to surcharge
(i)on stable soils with an allowable bearing pressure of 75 kPa or greater, and
(ii)for buildings of wood-frame construction, and
(c)flat insulating concrete form foundation walls and concrete footings not subject to surcharge (See Note A-9.15.1.1.(1) (c) and 9.20.1.1.(1)(b))
(i)on stable soils with an allowable bearing pressure of 75 kPa or greater, and
(ii)for buildings of light-frame or flat insulating concrete form construction that are not more than 2 storeys in building height, with a maximum floor-to-floor height of 3 m.
(2)Foundations for applications other than as described in Sentence (1) shall be designed in accordance with Section 9.4.
(3)Where a foundation is erected on filled ground, peat or sensitive clay, the footing sizes shall be designed in conformance with Section 4.2.
(4)For the purpose of Sentence (3), sensitive clay means the grain size of the majority of the particles is smaller than 0.002 mm, including leda clay.
Open OBC Div. B 9.15.1.1. in the code viewer
OBC Div. B 9.15.3.3. Application of Footing Width and Area Requirements
(1)Except as provided in Sentence 9.15.3.4.(2), the minimum footing width or area requirements provided in Articles 9.15.3.4. to 9.15.3.7. shall apply to footings, where
(a)the footings support
(i)foundation walls of masonry, concrete, or flat insulating concrete form walls,
(ii)above ground walls of masonry, flat insulating concrete form walls or light wood-frame construction, and
(iii)floors and roofs of light wood-frame construction,
(b)the span of supported joists does not exceed 4.9 m, and
(c)the specified live load on any floor supported by the footing does not exceed 2.4 kPa. (See Table 4.1.5.3.)
(2)Except as provided in Sentence 9.15.3.4.(2), where the span of the supported joists exceeds 4.9 m, footings shall be designed in accordance with Section 4.2.
(3)Where the specified live load exceeds 2.4 kPa footings shall be designed in accordance with Section 4.2.
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OBC Div. B Table 9.15.3.4. Minimum Footing Sizes — Forming Part of Sentence 9.15.3.4.(1)
Table 9.15.3.4 — Minimum Footing Sizes — Forming Part of Sentence 9.15.3.4.(1) Forming Part of Sentence 9.15.3.4.(1) Number of Floors Supported | Minimum Width of Strip Footings Supporting Exterior Walls[2], mm | Minimum Width of Strip Footings Supporting Interior Walls[3], mm | Minimum Footing Area for Columns Spaced 3 m o.c.[1], m² 1 | 250 | 200 | 0.40 2 | 350 | 350 | 0.75 3 | 450 | 500 | 1.0 Notes to Table 9.15.3.4.: (1) See Sentence 9.15.3.7.(1). (2) See Sentences 9.15.3.5.(1). (3) See Sentence 9.15.3.6.(1).
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OBC Div. B 9.15.3.5. Adjustments to Footing Widths for Exterior Walls
(1)The strip footing widths for exterior walls shown in Table 9.15.3.4. shall be increased by
(a)65 mm for each storey of masonry veneer over wood-frame construction supported by the foundation wall,
(b)130 mm for each storey of masonry construction supported by the foundation wall, and
(c)150 mm for each storey of flat insulating concrete form wall construction supported by the foundation wall.
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OBC Div. B 9.15.3.8. Footing Thickness
(1)Footing thickness shall be not less than the greater of
(a)100 mm, or
(b)the width of the projection of the footing beyond the supported element.
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OBC Div. B Table 9.15.4.2-A. Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m
Table 9.15.4.2.-A. — Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m Forming Part of Sentence 9.15.4.2.(1) Solid concrete and concrete core in flat wall insulating concrete forms[3], 15 MPa min. strength Minimum Thickness of Concrete or Concrete Block, mm | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Unsupported at the Top[1][2] ≤ 3.0 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] ≤ 2.5 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] > 2.5 m and ≤ 2.75 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] > 2.75 m and ≤ 3.0 m) 150 | 0.8 | 1.5 | 1.5 | 1.4 200 | 1.2 | 2.15 | 2.15 | 2.1 250 | 1.4 | 2.3 | 2.6 | 2.5 300 | 1.5 | 2.3 | 2.6 | 2.85 Solid concrete and concrete core in flat wall insulating concrete forms[3], 20 MPa min. strength Table 9.15.4.2.-A. — Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m Minimum Thickness of Concrete or Concrete Block, mm | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Unsupported at the Top[1][2] ≤ 3.0 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] ≤ 2.5 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] > 2.5 m and ≤ 2.75 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] > 2.75 m and ≤ 3.0 m) 150 | 0.8 | 1.8 | 1.6 | 1.6 200 | 1.2 | 2.3 | 2.3 | 2.2 250 | 1.4 | 2.3 | 2.6 | 2.85 300 | 1.5 | 2.3 | 2.6 | 2.85 Unreinforced concrete block Table 9.15.4.2.-A. — Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m Minimum Thickness of Concrete or Concrete Block, mm | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Unsupported at the Top[1][2] ≤ 3.0 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] ≤ 2.5 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] > 2.5 m and ≤ 2.75 m) | Maximum Height of Finish Ground Above Basement Floor or Crawl Space Ground Cover, m (Height of Foundation Wall Laterally Supported at the Top[1][2] > 2.75 m and ≤ 3.0 m) 140 | 0.6 | 0.8 | N/A | N/A 190 | 0.9 | 1.2 | [4] | [4] 240 | 1.2 | 1.8 | [4] | [4] 290 | 1.4 | 2.2 | N/A | N/A Notes to Table 9.15.4.2.-A: (1) See Article 9.15.4.3. (2) See Article 9.15.4.6. (3) See Note A-Table 9.15.4.2.-A. (4) See Table 9.15.4.2.-B.
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OBC Div. B 9.15.4.3. Foundation Walls Considered to be Laterally Supported at the Top
(1)Sentences (2) to (4) pertain to lateral support for walls described in Sentence 9.15.4.2.(1).
(2)Foundation walls shall be considered to be laterally supported at the top if
(a)such walls support a solid masonry superstructure or flat insulating concrete form wall,
(b)the floor joists are embedded in the top of the foundation walls,
(c)the floor system is anchored to the top of the foundation walls with anchor bolts, in which case the joists may run either parallel or perpendicular to the foundation walls, or
(d)they extend from the footing to no more than 300 mm above the finished ground level and are backfilled on both sides such that the difference in elevation between the finished ground levels on either side of the wall is no more than 150 mm.
(3)Unless the wall around an opening is reinforced to withstand earth pressure, the portion of the foundation wall beneath an opening shall be considered laterally unsupported if
(a)the opening is more than 1.2 m wide, or
(b)the total width of the openings in the foundation wall constitutes more than 25% of the length of the wall.
(4)For the purposes of Sentence (3), the combined width of the openings shall be considered as a single opening if the average width is greater than the width of solid wall between them.
(5)Flat insulating concrete form foundation walls shall be considered to be laterally supported at the top if the floor joists are installed according to Article 9.20.17.5.
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OBC Div. B 9.15.4.6. Extension Above Ground Level
(1)Exterior foundation walls shall extend not less than 150 mm above finished ground level.
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OBC Div. B 9.15.5.2. Support of Beams
(1)Not less than a 190 mm depth of solid masonry shall be provided beneath beams supported on masonry.
(2)Where the beam referred to in Sentence (1) is supported below the top of the foundation walls, the ends of such beams shall be protected from the weather.
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OBC Div. B 9.16.2.1. Required Installation of Granular Fill
(1)Except as provided in Sentence (2), not less than 100 mm of coarse clean granular material containing not more than 10% of material that will pass a 4 mm sieve shall be placed beneath floors-on-ground. (See also Subsection 9.13.4. and Note A-9.13.4.)
(2)Granular material need not be installed under
(a)slabs in garages, carports or accessory buildings, or
(b)buildings of industrial occupancy where the nature of the process contained therein permits or requires the use of large openings in the building envelope even during the winter.
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OBC Div. B 9.16.4.3. Thickness
(1)Concrete slabs shall be not less than 75 mm thick exclusive of concrete topping. (See Note A-9.16.4.3.(1))
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