How Much Space Do You Need Between Composite Decking Joists

Henry A
Composite decking joist

A well-designed frame is essential if you want a safe, reliable, and long-lasting ultra decking. Every decision you make regarding your decking frame affects the overall outcome of the deck. One of the questions that you may encounter is about the joist spacing. All decking joists need spacing. But the question is, how much space do you need between the composite decking joist? And why is it crucial to make the right decision?

Composite decking joist

Why is Proper Joist Spacing Is Important?

Joist spacing affects several things. As such, people who want to build decks should pay close attention to them. The reason why it matters so much is that it determines the load-bearing capacity of your decking.

If you space them too far, the decking boards have less support. Less support means the decking will be more prone to sagging. Exposing it to high foot traffic can snap the boards, leading to expensive repairs and dangerous accidents.

On the other hand, spacing them too near each other offer the best structural strength. The downside is, you will be using more wood, screws, and other materials for the decking. You also have to spend more time and effort in installing the decking boards. It will cost you more money and energy.

How Much Space Do You Need?

Joist spacing refers to the distance between the centre of one joist to the other. The term used is on-centre or OC. You’ll have to be careful not measure it from one edge to the other. Alternatively, you can subtract the joist width from the recommended joist spacing if you want to measure it from edge to edge. But the question is, how much space is needed?

There are several options for joist spacing, namely 12″, 16″, 24″. While it may seem easy to pick one from the three, there are several things you will need to consider first to get the best choice.

For residential properties, 16″ OC is the go-to joist spacing. It’s usually the standard for many building codes, thus the most widely used spacing. On the other hand, though not as common as 16″, 24″ OC is another option for houses. However, you may need to use thicker boards, or the floor will sag. It’s also not suited for areas with foot traffic. It’s not recommended for elevated decks or ones that require permission planning.

While some use 12″ OC spacing for residential decking, it’s more common in non-residential areas. Decks on commercial and public establishments will bear higher foot traffic. With that in mind, they require sturdier and stronger floors. The downside to having only 12″ OC spacing is that it can contribute to a more expensive decking.

Follow the Manufacturer’s Guidelines

The best way to know how much space you need between composite decking joists is to ask your decking board manufacturers. They can give you more specific information on building a subframe for their products, including joist spacing instructions. Following their guidelines, if any, also protects you and the products and keeps the warranties valid.

Next, you will also need to follow your local building codes. The standards are there to keep you safe and ensure the structural integrity of the decking. While you may not necessarily need to follow the requirements in some instances, such as building a ground-level deck, it’s still best to consider them.


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