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.

    (2)  Except as provided in Sentences (4) and (5), 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).

    (3)  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

    (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.

    (4)  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.

    (5)  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.

    (6)  Where drainage is required in Sentence (1), the drainage shall conform to Subsection 9.14.3. or 9.14.4.

Article Ontario Regulation 332/12 Building Code,   Information published by for educational purposes only.

Foundation drainage is required unless it can be shown that natural, free-draining soil makes it unnecessary. Foundation drainage normally consists of a drain pipe installed around the perimeter of the basement and usually a wall drainage layer. A layer of granular material can be used in lieu of a perimeter drain for foundations such as preserved wood foundations, where the granular layer slopes to a sump.

Adequate drainage is essential to prevent the infiltration of water into the basement. Drain pipe should be laid on solid undisturbed soil around the footings, with the top of the pipe below the level of the basement floor or crawl space, and with a slight slope to the outlet. Cover the pipe with a minimum of 150 mm (6 in.) of coarse, clean gravel or crushed rock (Figure 50). The pipe should be wrapped with a filter fabric “sock” to prevent fine particles in the backfill from clogging the drain. Backfill must not contain pyritic shale or materials finer than 4 mm (5⁄32 in.).

Connect the drain pipe with a tight joint to a storm sewer or other satisfactory outlet. A sump may be necessary in some cases.

On wet sites, special drainage features such as lateral drain pipes under the floor slab may be needed to avoid hydrostatic pressures on basement walls and slab. Note that foundation drainage is not intended to deal with high water tables. Foundations located on sites with high water tables must be designed by an engineer.

Figure 50

Drain pipe at foundation wall

Source : Canada Mortgage and Housing Corporation (CMHC)