Installing a durable, low-maintenance composite deck is a great way to enhance your outdoor living space. Properly spacing the deck joists is critical to providing adequate support for composite decking materials just as it is for lumber. This guide covers the ideal joist spacing for composite decks to help ensure your new deck stands the test of time.
What is Composite Decking?
Composite decking is made from a combination of wood fibers and recycled plastic polymers. Brands like Trex, TimberTech and Fiberon are popular composite decking manufacturers.
Composites provide benefits like:
- Resistance to weather, stains, rotting and insects
- Cooler surface in hot weather vs traditional wood
- Splinter-free and easy on bare feet
- Low maintenance – no sanding, staining or sealing required
Joist Spacing Guidelines for Composite Decks
Joists are the critical horizontal support framing in your deck structure. Properly spacing deck joists ensures composite deck boards remain flat and sturdy underfoot.
Standard Joist Spacing
The typical joist spacing guidelines for composite decking are:
- 16 inches on-center – The most common joist spacing for composite decks
- 12 inches on-center – Recommended for angled decking patterns or heavy items like hot tubs
- 24 inches on-center – Only recommended for straight deck board patterns on shorter deck spans
Follow Manufacturer Recommendations
Decking brands like Trex and TimberTech provide span charts to ensure proper joist sizing and spacing per individual product lines. Consult the manufacturer guidelines for your specific composite product.
Adhere to Local Building Codes
Your city may mandate joist sizing and spacing requirements. Common code maximums are 16 inch on-center spacing and 24 inch max joist spans depending on joist dimensions.
Building permits generally require compliance with local codes.
How Far Apart Should Composite Deck Joists Be?
For a standard residential composite deck build, here are typical joist spacing distances:
- 12 inches on-center – Joists spaced 12″ apart from center of one joist to center of the next joist
- 16 inches on-center – Joists spaced 16″ apart from center to center
- 24 inches on-center – Joists can be spaced 24″ apart but only for short spans under 10 feet with straight board patterns
Wider joist spacing beyond 16″ on-center is only recommended for shorter decks using solid composite decking materials, not hollow profiles.
Maximum Joist Spacing for Composite Decks
It’s recommended to space composite deck joists:
- No more than 16 inches on-center for most residential deck builds
- Up to 24 inches on-center only for straight board patterns on shorter deck spans under 10 feet
- Closer than 12 inches on-center if angled deck patterns are planned
Exceeding 16 inches on-center spacing risks excessive bounce or sagging over time as composite boards deform under weight. Strengthen joists and reduce spacing for heavy loads like hot tubs.
Joist Span Lengths for Composite Decking
Proper joist sizing is critical to maintain strength across required lengths. The joist length or span between supports impacts spacing needs.
Typical maximum joist spans for composite decks:
- 2×8 joists – 10 ft. span
- 2×10 joists – 14 ft. span
- 2×12 joists – 18 ft. span
Consult deck framing span tables to ensure your joist dimensions work for the required deck length.
Special Considerations for PVC and Other Composite Decking
- PVC Decking – Premium PVC decking brands like AZEK allow joist spacing up to 24″ on-center. Check manufacturer specs.
- Heavy Items – Tubs, planters, etc need 12″ joist spacing or supplemental blocking between joists.
- Angled Decking – Diagonal or herringbone composite patterns require tighter 12″ joist spacing.
Q: What is the recommended joist spacing for composite decking?
A: The recommended joist spacing for composite decking is typically 16 inches on center. However, it is important to consult the installation instructions provided by the manufacturer of the decking material you are using, as spacing requirements may vary.
Q: Can I use a larger joist spacing for composite decking?
A: While it is possible to use a larger joist spacing for composite decking, it is not recommended. A larger spacing may result in sagging or bowing of the deck boards over time, compromising the overall stability and durability of the deck.
Q: What is the maximum joist span for composite decking?
A: The maximum joist span for composite decking depends on various factors, including the thickness and strength of the decking material, as well as the joist size and spacing. It is best to consult the span tables provided by the manufacturer of the decking material you are using to determine the maximum joist span.
Q: Can I install composite decking with 24-inch joist spacing?
A: Yes, you can install composite decking with 24-inch joist spacing. However, it is important to ensure that the decking material you are using is specifically rated for this spacing. Some decking brands may require a smaller joist spacing for optimal performance.
Q: Should I use composite joists for composite decking?
A: While it is not necessary to use composite joists for composite decking, it is recommended for optimal performance. Composite joists are specifically designed to be resistant to moisture and rot, making them an ideal choice for supporting composite decking.
Q: Can I use wood joists for composite decking?
A: Yes, you can use wood joists for composite decking. However, it is important to ensure that the wood joists are properly treated and have sufficient strength to support the weight of the decking material and any additional loads, such as furniture or people.
Q: What is the best way to fasten composite decking to the joists?
A: The best way to fasten composite decking to the joists is to use hidden fasteners. Hidden fasteners provide a clean and seamless appearance, as they are not visible on the surface of the deck. They also help to prevent the risk of splintering or warping that can occur with traditional face-fastening methods.
Q: What are some popular composite decking brands?
A: Some popular composite decking brands include Trex, TimberTech, Fiberon, and Azek. These brands offer a wide range of composite decking options with various colors, textures, and durability characteristics.
Q: Can I install railing on a composite decking?
A: Yes, you can install railing on a composite decking. Many composite decking brands offer compatible railing systems that are specifically designed to complement their decking products. It is important to follow the manufacturer’s installation guidelines for proper installation of the railing.
Q: What are the benefits of using composite decking?
A: Some benefits of using composite decking include its durability, low maintenance requirements, resistance to rot and pests, and its ability to mimic the appearance of natural wood. Composite decking is also an eco-friendly choice, as it is often made from recycled materials.
Key Takeaways for Proper Joist Spacing
- Most composite decks require joists 16″ on-center spacing
- Adhere to manufacturer span charts for your specific decking
- Follow local building codes for permitted joist sizing and gaps
- Limit joist spans to 10-14ft depending on joist size
- Consider 12″ joist spacing for heavy objects or diagonal decking
With proper joist installation and spacing, your new composite deck will provide lasting stability and enjoyment for decades to come. Consult a professional deck builder to ensure your joists comply with all requirements.
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