How Far Apart Should You Place Your Joists?

M. John
Joist consideration, decking base planning

Composite decking is the leading choice for homeowners. Composite materials are a durable and beautiful decking option made from recycled plastic and reclaimed wood. Not only is it reliable, but it’s eco-friendly as well. Aside from that, it’s also cheaper than regular decking when compared in the long term.

Another great thing about composite decking is the ease of installation. You don’t need to cut, treat, or sand the materials. Instead, you can immediately start working with them. In some cases, you can also have the materials measured and customised. One of the best conveniences of using composite materials is that they don’t require any complicated foundation. You don’t have to lay a solid foundation or set up concrete for your composite decking. Instead, you will only need a basic joist frame to act as the foundation.

However, here’s what is confusing for many people: how close should joists be when using composite materials?

A strong foundation is the first step to a well-built decking. To ensure long-lasting composite decking, the precise placing of the deck joists is crucial. If you want to install decking in your outdoor space, you should place the joists accurately. This article will shed light on joist spacing for composite decking. It will also discuss how far apart you should place your joists.

What Are Decking Floor Joists?

Deck joists are horizontal beams that make up the frame that supports the deck. The joists are important to perfect the deck. It functions as a support for the deck, ensuring that the decking weight is evenly distributed. When building your decking, you have to place the deck joists correctly and ensure they are properly spaced apart.

How Far Apart Should You Place Your Joists


Why Is Joist Spacing Important?

Joist spacing is very crucial in decking buildings. Correct spacing of the joists will prevent your ultra-decking from sagging. If the decking joists are placed too far apart, it will cause the composite decking to spring and sag. In addition, if the joist height is not equal to each other, it can also cause an uneven decking surface. To keep that from happening, appropriate spacing of the joists is important as they serve as the foundation for the deck. If the foundation is not installed properly, it will surely affect the decking. The decking space should not be too far apart, nor should it be too close. So, how far apart should you install your decking joist?

How Far Apart Should You Place Your Joists?

Most composite decking manufacturers have guidelines on the length of joist spacing for their decking. When you purchase a decking, you should ask your supplier or manufacturer what are the decking joists guidelines during installation. So, how far apart should you place the joists? Subject to the brand of composite decking you choose, some manufacturers recommend maximum joist spacing of 30cm (300mm) on centres, 35cm (350mm) on centre and 40cm (400cm) on centre. When installing the joists, you must follow the manufacturer’s guidelines. There are various guidelines for placing joists for different decking sizes and brands.

Additionally, joist spacing also depends on the angle and length of your decking. Some brands recommend 40cm (400mm) at the centre for 90 degree angles. And also, 35cm (350mm) on the centre for 30-degree angles and 30cm (300mm) for 45-degree angles.

For residential decking, the joist space should not exceed 30cm (300mm), as measured in the centre. But if you want a more rigid feel for your decking, you can space the joists 20cm (200cm) in the centre. Please note: Lower joists centres will require additional accessories. Additionally, for commercial decking, the standard joist spacing is 20cm (200mm) in the centre using either a circular hollow or solid core composite decking board to compensate for the additional footfall and weight. Some areas in the UK have building regulations for deck joist spacing. You should always check for the recommended joist building regulations if required with your local authority to know exactly the appropriate joist spacing for composite decking and how the joists should be correctly installed?

Tips For Properly Installing Composite Decking Joist

First, when placing a joist for composite decking, you should ensure that the joist is level. You can do that by running a string line across the top of the joists. If any of the joists are too high these should be cut to the same level as the others. For any joists that are lower add shims to make them level.

Secondly, you should ensure that the joist is structurally sound. You can do this by using blocking to support the joist. Blocking involves installing small pieces of wood between the joists. It increases rigidity, and it also prevents sagging or twisting of the joist.

Lastly, you should cross-check your work. Check for protruding nails and screws. Take your time to inspect the joist can add to the lifespan of your decking. Always check your work to ensure the joists are properly placed.


Always follow the manufacturer’s guidelines. Depending on the brand and type of composite decking purchased the manufacturers guidelines for joist spacing can vary from product to product.


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