How Far Apart Are Joist on a Composite Decking

Henry A
composite decking joist

Creating a well-designed frame is crucial for a deck’s safety and structural stability. One of the most important details you have to pay attention to is the joists, especially the spacing between them. But how does joist spacing affect your ultra decking performance? And how far apart are joist on a composite decking.

composite decking joist

Why Are Joists Spacing Crucial?

Joist spacing is a crucial detail in building a decking frame. It determines the rigidity of the floors. If you space them too far, the decking boards will sag. Sagging decking boards are likely to break more often due to heavy loads, leading to unwanted accidents. There is no disadvantage of spacing the joists too near to each other in terms of structural integrity. However, the downside is that you’ll be spending more on materials and putting more time and effort into building the deck. A few people also don’t like too rigid floorboards.

Joist spacing is measured by OC or on-centre. On-centre is the distance between the middle of one joist to the other, not from edge-to-edge. If you want to measure from edge-to-edge, you will need to measure the joist’s width and subtract it to your preferred spacing. That will be the actual space between the edges of the floor joists. Being familiar with this detail can help you build a better decking frame.

The Best Joist Spacing Distance

You have several choices when it comes to choosing the right joist spacing for your composite decking. In most cases, it boils down to three options, 12″, 16″, and 24″. In general, 16″ OC is considered the best option. However, there are some instances that the other two can be beneficial. But what are the advantages of each one?

12 Inches On-Centre –  12″ OC is the least cost-efficient joist spacing option among the three. Since there will be more joists, you will need more screws to drill the boards with and more materials for the frame. While still used, it is an uncommon option for residential decking. But for commercial places or areas with high foot traffic, the joist spacing is more likely 12″ OC for better durability and load-bearing ability. Unless you want a sturdier floor, 12″ OC is the least of your options.

deck joist space

16 Inches On-Centre – 16″ OC is the most recommended option by professional and experienced builders. It’s the most widely used joist spacing, both for residential or commercial premises. If you are building a standard composite decking, it’s your best option.

24 Inches On-Centre – White not as recommended as 16″ OC, but many still use 24″ OC for joist spacing. The main advantage of such spanning is that it uses fewer materials. However, the decking floors will be not as sturdy if you spaced the joists too far. It’s also not suited for places with high foot traffic. You can reinforce the floors by using thicker decking boards. However, thicker boards are usually more expensive. If your composite decking will not bear much foot traffic, then 24″ OC is a suitable option.

Overall, 16″ OC is the surest and most failproof joist spacing option. It’s not as cost-efficient as 24″, but it offers better durability and stability. However, before deciding on the joist spacing, you may also want to check your local building regulations for safety and compliance with the law. You can also ask your boards’ manufacturers or suppliers regarding this matter.

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