2024 OBC Guide: Maximum Spans for Built-up Floor Beams (Table 9.23.4.2.-J)
Sarah's Expert Insight
OBC Compliance Specialist
"As the senior consultant at empcontracting.ca Inc. your construction contractor in London, Ontario, I cannot overstate the importance of calculating 'supported length' correctly, especially in custom builds across Oakville and Muskoka where open-concept layouts are common. Incorrectly sizing a 5-ply beam for a three-story load can lead to significant floor deflection or structural failure; always ensure your bearing lengths meet the 152 mm requirement for longer supported spans to maintain the structural integrity of the home."
In Ontario residential construction, understanding the load-bearing capacities of built-up wood beams is essential for ensuring structural safety and code compliance. Table 9.23.4.2.-J of the 2024 Building Code Compendium specifies the maximum clear spans for floor beams supporting up to three stories.
Structural Requirements for Built-up Beams
The spans listed in this table are specifically designed for floors serving residential areas. These calculations vary based on the commercial designation of the lumber, the grade (Select Structural vs. No. 1 and No. 2), and the number of plies (3-ply, 4-ply, or 5-ply) used in the assembly. At empcontracting.ca Inc. your construction contractor in London, Ontario, we ensure every beam is sized to meet these rigorous standards.
Supported Length and Lumber Species
Spans are determined by the 'supported length,' which is defined as half the sum of the joist spans on both sides of the beam. The table provides data for two primary groups:
- Spruce-Pine-Fir (SPF): Includes common species like Jack Pine and Balsam Fir, often preferred for their strength-to-weight ratio.
- Northern Species: Covers various Canadian species graded under NLGA rules.
Critical Installation Notes
According to the 2024 OBC, builders must account for specific site conditions that modify these span limits:
- Concrete Topping: If a floor includes a concrete topping (up to 51 mm), the allowable spans must be reduced by a factor of 0.8.
- Bearing Lengths: While standard beams require 114 mm of bearing, 3-ply beams with supported lengths exceeding 4.2 m require a minimum bearing length of 152 mm.
- Interpolation: Straight interpolation is permitted for supported lengths that fall between the values listed in the table.
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.