Date of Publication:  July 17, 2025    [2022.07.V-02.C]

Subject: Foundation Wall Drainage Layer Location 2024 OBC UPDATE

Summary of updates: Referenced sentences updated. Recommendation remains the same.

2024 Ontario Building Code [O.Reg 163/24 Amended to 5/25] Reference(s):

Article 9.13.2.1 of Div. B.

Article 9.14.2.1 of Div. B.

Incoming Request: 

Is it permissible to omit the drainage layer on the foundation wall separating the unexcavated garage from the interior full basement space?

Discussion & Considerations:

Assuming insulation is required to extend to more than 900mm below the exterior grade, dampproofing or waterproofing is required (9.13.2.1.(1), 9.13.2.1.(4). If dampproofing is provided, then a drainage layer must be provided. Sentence 9.14.2.1. allows different materials for this drainage layer. The question really boils down to three points:

• Should the foundation wall between the interior basement and the unexcavated garage be considered to “contain(s) the building interior” for the purposes of 9.14.2.1.(1)?

1. Yes, the basement can be considered the interior of a house.

• Should the interior slab of a garage be considered “adjacent exterior ground level” for the purposes of 9.14.2.1.(1.1)?

1. While this area may not be subject to the same precipitation and moisture as an uncovered, unenclosed ground surface, it may be subject to moisture from snow or rain brought in on vehicles or from surface runoff if not properly graded or garage doors are left open.

• Should the interior slab of a garage be considered “exterior finished ground level” for the purposes of 9.13.2.1.(1).?
  1. See above.

Generally the OBC speaks of exterior walls as separating conditioned from unconditioned space. Since insulation is required on the wall between the unexcavated garage and the basement interior, it is reasonable to apply this principle to the foundation wall in question as well.

Risk/Benefit Analysis:

It has been argued that garage interior space is not subject to the same rain, snow and temperature changes that a fully exterior space is subject to, and as a result the walls in question may be less subject to water ingress. The Objectives and Functional Statements indicate that preventing water ingress is the primary goal of these code clauses. Omission of a drainage layer on the wall in question could lead to moisture entering the building, which could expose a municipality to liability.

The only benefit here is to the constructor who may save a small amount of money by omitting a portion of drainage layer.

Other considerations:

BCC Ruling:

The BCAS Working Group recognizes that the Building Code Commission issued Ruling No. 03- 27-925, re: Application No. 2003-14 that involved a dispute with the Town of Grimbsy, regarding a foundation wall located under the garage, which had not been provided with a drainage layer. Without specifics regarding that particular site, our committee acknowledges it and remains confident it in its final guidance.

Final Recommendation:

Based on the information above, it is the opinion of the BCAS that a drainage layer is required on the foundation wall separating an unexcavated garage from a basement interior.

 Potential Exceptions:

The BCAS believes there are potential scenarios involving walkout or lookout basements with complex designs and/or stepped footings and foundations, which may change the final recommendation herein.

Referenced Documents:

 2024 OBC [O.Reg 163/24 Amended to 5/25]

Article 9.13.2.1 of Div. B.

Article 9.14.2.1 of Div. B.

Disclaimer:

This guidance document is intended to assist building officials by gathering relevant information to interpret the OBC Act and the prescriptive requirements of the Ontario Building Code, and is intended to be a best practice aid for building officials.

The views expressed within this guidance document should not be considered as the official interpretation of legislated requirements based on the Ontario Building Code, as the final responsibility for interpretation rests with the local Authority Having Jurisdiction. 

The views of this advisory committee should not be construed as legal advice.