When building a deck, one of the most critical decisions is determining the spacing of your deck joists. The answer to “How far apart should deck joists be?” depends on two key factors: the type of deck boards you’re installing and your local building codes. Let’s break it down to help you make an informed choice for a sturdy, long-lasting deck.
Standard Joist Spacing: 16 Inches On Center
In most areas, the standard spacing for deck joists is 16 inches on center (OC). This measurement refers to the distance from the center of one joist to the center of the next.
This spacing works well for traditional pressure-treated wood or softwood decking, providing a solid foundation that balances strength and material efficiency. However, always check your local building codes, as they may have specific requirements that override general standards.
Composite and PVC Deck Boards: Consider 12-Inch Spacing
If you’re installing composite or PVC deck boards, you may need to adjust your joist spacing. These materials are more flexible than traditional wood, especially in hot weather when they can soften under the sun’s heat.
This flexibility can lead to sagging between joists, creating a wavy appearance on your deck surface. The dips between joists become visually noticeable, detracting from the deck’s aesthetics and potentially affecting its structural integrity.
To prevent this, many contractors recommend 12-inch on-center joist spacing for composite or PVC decking. The closer spacing provides additional support, minimizing sagging and ensuring a smooth, even surface. Check the manufacturer’s recommendations for your specific decking material, as some brands may explicitly require 12-inch spacing to maintain warranties or performance standards. Many composite and PVC decking manufacturers have smaller spacing requirements on deck stairs often around 8 inches on center.
Hardwood Decking: Up to 24 Inches On Center (With Caution)
For those opting for hardwood decking boards like Ipe, Cumaru, Garapa, or Tigerwood, you’re working with some of the hardest and most durable woods available. These species are incredibly strong and can often span up to 24 inches on center without compromising stability. Wider spacing can reduce the number of joists needed, potentially lowering material costs.
However, before spacing joists at 24 inches OC, consult your local building codes. Many jurisdictions restrict joist spacing to 16 inches or less, regardless of the decking material, to ensure safety and compliance. Additionally, verify the specific requirements for your chosen hardwood species, as factors like board thickness and joist size can influence the allowable span.
Key Considerations for Joist Spacing
To ensure your deck is safe, durable, and visually appealing, keep these tips in mind:
- Check Local Building Codes: Always confirm joist spacing requirements with your local permitting office, as codes vary by region.
- Follow Manufacturer Guidelines: Deck board manufacturers often specify maximum joist spacing to ensure performance and warranty coverage.
- Consider Environmental Factors: In hot climates, composite and PVC decking may require tighter spacing to prevent sagging.
- Account for Deck Design: Diagonal or herringbone decking patterns may require closer joist spacing to support the angled boards adequately.
- Use Proper Joist Sizing: The size of your joists (e.g., 2×8, 2×10) must align with the span and spacing to meet load requirements.
Conclusion
The ideal deck joist spacing depends on your decking material and local regulations. For most traditional wood decks, 16 inches on center is the standard. For composite or PVC decking, consider 12 inches on center to prevent sagging and maintain a smooth surface. With hardwood decking like Ipe or Cumaru, you might span up to 24 inches on center, but only if permitted by local codes. By aligning your joist spacing with your deck boards’ requirements and local standards, you’ll build a deck that’s both structurally sound and visually stunning.