OBC 2024 Guide: Maximum Spans for Built-up Floor Beams (Table 9.23.4.2.-I)
Sarah's Expert Insight
OBC Compliance Specialist
"In my experience, many DIY builders overlook Note 2 regarding concrete toppings; failing to apply the 0.8 reduction factor for radiant floor systems is a common reason for failed inspections in London and Muskoka. At empcontracting.ca Inc. your construction contractor in London, Ontario, we always cross-reference the supported length with the bearing requirements to ensure the floor system feels stiff and exceeds the minimum safety requirements of the OBC."
Table 9.23.4.2.-I of the 2024 Ontario Building Code (OBC) Compendium outlines the structural requirements for built-up floor beams in residential settings. When planning your next renovation or new build, consulting with empcontracting.ca Inc. your construction contractor in London, Ontario ensures that your framing meets these rigorous safety standards for beams supporting up to two floors.
Understanding Maximum Spans for Built-up Floor Beams
The maximum allowable span of a beam is determined by the species of wood, its commercial grade, the number of plies (size of the built-up beam), and the supported length. The OBC provides specific data for both Spruce-Pine-Fir (SPF) and Northern Species, covering grades from Select Structural down to No. 1 and No. 2.
Material Species and Grading
Spruce-Pine-Fir (SPF) is a common choice for framing in Southern Ontario. According to the table, a 5-ply 38 x 286 mm SPF Select Structural beam can achieve a maximum span of 4.87m under a 2.4m supported length. However, if the supported length increases to 6.0m, the maximum span reduces to 3.14m to maintain structural integrity.
Calculation of Supported Length and Clear Spans
Supported length is defined as half the sum of the joist spans on both sides of the beam. It is vital to note that the spans listed in the table are 'clear spans' between supports. For the total length of the beam, contractors must add the required bearing lengths at each end to ensure the beam is properly seated.
Critical Installation and Bearing Notes
Proper installation is just as important as sizing. The 2024 Building Code mandates specific bearing lengths to prevent wood crushing:
- 3-ply beams: Require a minimum bearing length of 114 mm.
- 4-ply and 5-ply beams: Require 114 mm if the supported length exceeds 3 m.
- Standard beams: Most other configurations require a minimum of 76 mm.
Impact of Concrete Toppings
Modern luxury homes in areas like Oakville and London often feature radiant in-floor heating. If the floor includes a concrete topping of up to 51 mm, the OBC requires the spans in Table 9.23.4.2.-I to be multiplied by 0.8. This 20% reduction accounts for the significant increase in dead load on the floor system.
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.