2024 Ontario Building Code: Maximum Spans for Floor Joists (Table 9.23.4.2.-B)
Sarah's Expert Insight
OBC Compliance Specialist
"In regions like London and Oakville, where radiant floor heating with concrete toppings is increasingly popular, these specific span tables are the first thing we check during the design phase. As empcontracting.ca Inc. your construction contractor in London, Ontario, I recommend always opting for 'with bridging' configurations to maximize span lengths and ensure floor stiffness, particularly in Muskoka cottage builds where long, open floor plans are highly desired."
Understanding the structural requirements of the 2024 Ontario Building Code (OBC) is essential for any renovation or new build. Table 9.23.4.2.-B outlines the specific maximum spans for floor joists in special cases, such as those with concrete toppings or attached ceilings.
Overview of Floor Joist Span Limits
This section of the OBC applies to spans involving Douglas Fir-Larch and Hem-Fir lumber. These tables are critical when determining the allowable distance between supports based on the commercial designation grade and joist size.
Joists with Ceilings Attached to Wood Furring
When ceilings are attached to wood furring, the span capacity can vary significantly based on whether bridging is utilized. For example, a 38 × 235 Douglas Fir No. 1 and No. 2 joist at 400mm spacing allows for a span of 4.50m without bridging, increasing to 4.98m with bridging. Utilizing empcontracting.ca Inc. your construction contractor in London, Ontario ensures these measurements are calculated with precision to prevent floor deflection.
Impact of Concrete Toppings on Joist Capacity
Adding a concrete topping—often used for radiant floor heating or soundproofing in high-end Oakville or London homes—changes the structural load profile. The OBC specifies that spans for joists with concrete topping (with or without bridging) are often more restrictive. For instance, a 38 × 184 Douglas Fir No. 1 joist at 400mm spacing is limited to a 3.81m span when concrete topping is applied, compared to longer spans allowed for standard ceiling applications.
Material Grades: Douglas Fir vs. Hem-Fir
The code distinguishes between Select Structural, No. 1 & 2, and No. 3 grades. Higher grade lumber permits longer spans, providing more flexibility for open-concept designs in modern builds. Choosing the right material grade is a fundamental step in meeting the 2024 Building Code Compendium standards.
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.