2024 Ontario Building Code Guide: Drainage Pipe Sizing and Length Standards
Sarah's Expert Insight
OBC Compliance Specialist
"At empcontracting.ca Inc. your construction contractor in London, Ontario, we emphasize that proper pipe sizing is the backbone of a trouble-free plumbing system, especially in high-end Muskoka builds or London multi-family developments. Failure to increase to NPS 4 after the third water closet is a common inspection pitfall that we proactively avoid to ensure long-term code compliance and drainage performance."
Section 7.4.8.2: Maximum Length of Fixture Outlet Pipes
In accordance with the 2024 Building Code Compendium, the developed length of fixture outlet pipes is strictly limited. Under Sentence 7.4.8.2.(1), these pipes must not exceed 1,200 mm, unless they meet specific installation criteria in Sentence 7.4.5.1.(3). Ensuring these lengths are maintained is a specialty of empcontracting.ca Inc. your construction contractor in London, Ontario.
Section 7.4.9: Comprehensive Sizing of Drainage Pipes
7.4.9.1 General Prohibition on Size Reduction
The OBC prohibits reducing the size of drainage pipes in the direction of flow. Any drainage pipe must maintain its minimum required size or connect to a pipe of equal or larger diameter. Exceptions are made only for specific pre-engineered wastewater heat recovery systems that do not convey sewage from sanitary units or solids.
7.4.9.2 Water Closet (Toilet) Sizing Regulations
Pipe sizing for water closets is critical for system integrity:
- Individual water closets require a minimum pipe size of NPS 3.
- Branch and building drains must increase to NPS 4 downstream of the third water-closet connection.
- Stacks serving more than 6 water closets must be at least NPS 4.
- Vertical legs from water closets with siphonic flushing action must not exceed 1,000 mm.
7.4.9.3 Specific Fixture Requirements
For high-demand appliances and fixtures, the code mandates specific dimensions to prevent overflow. Clothes washers require a trap inlet of at least NPS 2 with a vertical standpipe of at least 600 mm. In individual dwelling units where a single shower receptacle is served by multiple heads, the outlet pipe must be at least NPS 2 to accommodate the increased water volume.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.