Understanding Ontario Building Code Deck Joist Span Tables
When planning a deck construction project in Ontario, it's crucial to adhere to the provincial building code to ensure safety and structural integrity. One key aspect of this is understanding the deck joist span tables outlined in the Ontario Building Code (OBC). This guide will help you navigate these tables and provide insights into their application.
Why Deck Joist Span Tables Matter
Deck joist span tables are essential for determining the appropriate spacing between joists, a critical factor in ensuring your deck can safely support its intended load. The OBC provides these tables to help builders and homeowners make informed decisions about joist spacing based on the type of decking material and the expected live load.
Understanding Live Loads
Before diving into the tables, it's important to understand live loads. In the context of deck construction, live loads refer to the anticipated weight that the deck will bear, such as people, furniture, and snow. The OBC requires decks to be designed to support a minimum live load of 40 lbs per square foot (psf) for residential decks and 100 lbs psf for public decks.
Ontario Building Code Deck Joist Span Tables
The OBC provides two primary deck joist span tables: one for solid sawn decking and another for engineered wood decking. These tables consider the material's strength and stiffness to determine the maximum allowable span between joists.
Solid Sawn Decking Joist Span Table
| Joist Size (nominal) | Maximum Span (inches) |
|---|---|
| 2x6 | 16 |
| 2x8 | 24 |
| 2x10 | 32 |
| 2x12 | 40 |
For solid sawn decking, the maximum allowable span increases with the size of the joist. A 2x6 joist can span up to 16 inches, while a 2x12 joist can span up to 40 inches.
Engineered Wood Decking Joist Span Table
| Joist Size (nominal) | Maximum Span (inches) |
|---|---|
| 2x4 | 16 |
| 2x6 | 24 |
| 2x8 | 32 |
| 2x10 | 40 |
Engineered wood decking, such as I-joists, can span farther than solid sawn joists due to their increased strength and stiffness. A 2x4 engineered joist can span up to 16 inches, while a 2x10 joist can span up to 40 inches.
Adjusting for Load and Slope
The tables provided in the OBC assume a uniformly distributed live load of 40 lbs psf and a deck slope not exceeding 1/4 inch per foot. If your deck has a different live load or slope, you'll need to adjust the maximum allowable span accordingly. The OBC provides adjustment factors for these variables to help you determine the appropriate joist spacing.
Adjustment Factors
- Live Load Factor: Multiply the maximum span by the live load factor to account for loads greater than 40 lbs psf.
- Slope Factor: Divide the maximum span by the slope factor to account for decks with slopes greater than 1/4 inch per foot.
Additional Considerations
While the deck joist span tables provide a solid foundation for designing your deck, there are additional factors to consider:
- Concentrated Loads: Ensure joists can support concentrated loads, such as those from deck furniture or hot tubs.
- Edge Support: Provide adequate support for the outer edges of the deck to prevent joist sagging.
- Local Building Codes: Always check for local building codes that may have additional requirements or restrictions.
Conclusion
Understanding and correctly applying the Ontario Building Code deck joist span tables is crucial for constructing a safe and durable deck. By following the guidelines outlined in this article, you can ensure that your deck is designed to support its intended load and provide years of enjoyment. Always consult the latest version of the OBC and consider working with a professional if you're unsure about any aspect of your deck construction project.
