BCAB 2000 - Foundation wall drainage at interior locations

Foundation wall drainage at interior locations

Project Description

The project is the construction of a new house on a sloping site.  The bottom storey of the house will be set into the hillside and finished grade at the rear of the house will be 3.65 m higher than the grade at the front of the house.

To avoid bedrock and to reduce excavation volumes and foundation wall heights, the excavation will be stepped and the bottom storey will have steps in the floor levels.  Interior foundation walls, running perpendicular to the slope, will accommodate the different levels of the interior concrete floors-on-ground.

It is proposed that the rear side of the interior foundation walls be dampproofed and be equipped with a foundation drain pipe that connects to the foundation drain pipes at the exterior perimeter.

The configuration is generally as shown in the Schematic Illustration below:

Applicable Code requirements (BCBC 2024)

Sentence 9.14.2.1.(1), Division B, Foundation Wall Drainage

(1) Unless it can be shown to be unnecessary, the bottom of every exterior foundation wall shall be drained by drainage tile or pipe laid around the exterior of the foundation in conformance with Subsection 9.14.3. or by a layer of gravel or crushed rock in conformance with Subsection 9.14.4.

Sentence 9.14.3.3.(1), Division B, 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.

Sentence 9.16.3.1.(1), Division B, Control of Water Ingress

(1) Except as provided in Article 9.16.3.2. or where it can be shown to be unnecessary, ingress of water underneath a floor-on-ground shall be prevented by grading or drainage.

Decision being appealed (Local Authority’s position)

Sentence 9.14.2.1.(1), Division B, requires that foundation wall drainage pipes must be provided at the exterior (emphasis added) of foundation walls.  A drainage pipe at the interior of the building is not permitted.

Sentence 9.16.3.1.(1), Division B, refers to “grading” which would be at the exterior of the building, and to “drainage” which would also be at the exterior of the building.

Appellant's position

The Code requires the foundation wall drainage pipe to be located so the top of the pipe is below the underside of the basement slab.  Because the foundation and lower floor levels are stepped the only way to achieve this is to install a foundation wall drainage pipe adjacent to the foundation that runs through an interior area of the house.  Without this interior drainage pipe, groundwater travelling down the natural slope could bypass the upper foundation drainage pipe leaving the interior, lower foundation and adjacent basement slab unprotected.

The Code, as a minimum standard, requires drainage at the exterior but it also requires floors-on-ground to be protected.  If this interior foundation wall drainage pipe is not supported or required by Sentence 9.14.3.3.(1), Division B, then it is supported or required by Sentence 9.16.3.1.(1), Division B.

Appeal Board Final Decision #2000

The Board reverses the decision of the local authority.

It is the determination of the Board that the foundation wall drainage pipe in question protects the lower floor-on-ground and the Code does not prohibit its installation within the building footprint.

Reasons for Final Decision

Sentence 9.14.2.1.(1), Division B, requires foundation wall drainage at the exterior of the foundation walls and does not prohibit the installation of foundation wall drainage in other locations.

In this case, a foundation drainage pipe that is within the building footprint protects the lower floor-on-ground as required by Sentence 9.16.3.1.(1), Division B.

Don Pedde
Chair, Building Code Appeal Board

Dated:  June 18, 2026