Date of Publication: June 30, 2025 [2022.04.V-02.C]
Subject: Connection of Exterior Area Drains at Below Grade Entrances.- 2024 OBC Update
Summary of Updates: Changes to references, minor editorial change, no changes to recommendation.
2024 Ontario Building Code [O.Reg 163/24 Amended to 5/25] Reference(s):
Article 1.4.1.2. of Div. A
Article 7.1.1B.2. of Div. B
Sentence 7.1.2.2.(1) of Div. B
Sentence 9.14.6.1.(1) of Div. B
Sentence 9.31.4.3.(1) of Div. B.
Incoming Request:
A builder is constructing a new home with an exterior concrete stair leading to the basement. The property is served by both a storm sewer and a sanitary sewer. The Building Inspector has been called to the site to conduct a ‘building drain’ inspection. The Inspector reviews the drains for type of pipe, slope, property fittings, etc. but notices that the pipe leading from the exterior basement stair landing into the basement has been left open-ended (unconnected).
The builder installed a floor drain at the bottom of the stairs, and will connect it to a running trap (with a cleanout) under the basement floor slab, (inside, so it won’t freeze). She is asking for guidance, as one neighbouring municipality has required connecting it to the sanitary drain as the OBC says all floor drains must be connected to the storm drain, as rain water and melting snow will enter the floor drain. Yet another municipality has required that this builder connect the floor drain to the weeping tile.
Where should the floor drain connect to?
Executive Summary:
Exterior area drains that receive storm water must be directed to a storm drainage system, a dry well or drainage ditch. A floor drain that is fully enclosed within a building’s exterior walls should be treated as a floor drain and drain to a sanitary drainage system.
Discussion & Considerations:
This is commonly encountered when a below-grade entrance (BGE) is added to an existing building, however it is equally applicable to a BGE that is part of the initial construction of a building.
Enclosed stairs:
If the below grade entrance is fully enclosed by wood-frame or masonry exterior walls and a roof
meeting the applicable OBC requirements for walls and roofs, it can be considered to be part of
the interior of the building. In this case a drain located at the bottom of the stairs would be considered a floor drain, and would be permitted to drain to the sanitary drainage system. The drain would not be required if there were another floor drain present in the basement to satisfy the requirements of Sentences 9.31.4.3.(1) and/or Sentence 7.1.1B.2.(1) of Division B, although it may still be recommended.
Exterior stairs:
For a covered or uncovered stair (open to the exterior) an area drain must be provided to satisfy Sentence 9.14.6.1.(1). By definition, this water is storm water and must be directed to a storm drainage system, or “designated storm water disposal location” as required by Sentence 7.1.2.2.(1). Municipalities may also wish consider disposal to a dry well or a drainage ditch as described in Sentence 7.1.1B.2.(2) for a floor drain that receives storm drainage. It should also be noted that subsoil drainage pipes (weepers) are not considered part of a storm drainage system and storm sewage (such as that from an area drain) may not be directed to them. In a retrofit application a sump pit that discharges to a swale or dry well is the most common practical solution. Dry well and sump pit discharge pipe locations should be planned to minimize impact on neighboring properties. In a new build, a storm drainage pipe may easily be installed during inside drain installation to serve the area drain at the below grade entrance.
Risk/Benefit Analysis:
The risk associated with allowing storm drainage pipes to be connected to sanitary is that clean water is going to the treatment plant, and adding unnecessary operating costs for the municipality. During a large localized rainfall event, adding storm water to sanitary drains may result in surcharging of the sanitary and backflow of sewage to the interior of the house. Allowing area drains to connect to subsoil drainage pipes (weepers) may result in overloading of subsoil drainage system, clogging of subsoil drainage pipes with silt, leaves and other debris, resulting in poor drainage of the foundation wall and possible water ingress.
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.