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Composite decking framework

Once you’ve decided on the size and location of your deck, you’ll need to decide which decking boards you plan to use and which direction you want the boards to run in each area, as this will determine the amount and type of composite decking framework needed for your project.

Remember, if you’re going to build your decking next to your house, it will need to be below the damp proof course, you must make sure you don’t cover any air bricks and you’ll need to incorporate a fall to allow water to run off the surface of the deck. If you need help with any of these stages, your decking sales rep should be able to provide you with a step by step install guide, and if you’re not a confident DIYer then it’s easy to hire a professional landscaper via BALI or the APL.

What is the framework?

Decks are mainly all built of the same structure, which is a frame that is constructed from either treated timber, composite fibreglass or aluminium. The main part of your framework is the bearers which are the solid pieces that the boards are fixed to. Bearers take most of the weight from the decking and make sure your finished deck is safe and sturdy. A simple ground level deck is built close to the ground with your bearers laid directly onto a flat surface such as paving slabs.

What materials can you use?

Composite decking frames can be built from a variety of materials, but the choice you make is actually really important as it could affect the long term performance of your decking. Generally speaking, the cheaper the material, the more maintenance it will need and the sooner you’ll have to replace it, particularly if the ground you’re building is has poor drainage and there is a chance the composite decking beams of your frame might sit in standing water.

composite decking framework
wooden decking frame


Wood is a popular composite decking subframe choice as its relatively cheap and easy to source, but if you’re opting for wood it needs to be pressure treated and even then it’s prone to rotting, splitting and twisting as it absorbs a lot of water. Using wood will also change to type of framework you install versus composite or aluminium.
To prevent wooden bearers or joists twisting, bits of timber are sometimes fixed between them. These are called noggins and are staggered to enable them to be nailed into position through the joist and into the end of the noggin. If you know that your location is prone to a lot of rainfall or has poor drainage then you may want to consider alternative options to a wooden deck frame.


Building your subframe from composite bearers and joists is another option as they are water resistant, rot-free and will expand and contract in line with the composite decking. The cost may be a little higher than timber though, and you may not find as many options in terms of bearer thicknesses as you will from other materials.


The most common metal used for composite decking framework these days is aluminium, which has a superb resistance to fire and is both long-lasting and easy to work with. Aluminium won’t warp, sag or rot and will easily outlive the life of your decking boards. It can also span greater distances, and its only real disadvantage is its cost versus timber.

Joist spacing for composite decking

If you are laying your deck substructure yourself, you will need to carefully consider the appropriate joist spacing for composite decking. If your deck is a standard square or rectangular shape, start by making an outer frame. Make sure the corners are square, the frame rests flat and is totally supported. Now mark, cut and fit the intermediate bearers or joists, ensuring you check the maximum spacing limit span between each of them in accordance with your chosen decking manufacturer’s instructions.

In many cases, the maximum span beneath supporting bearers depends on the bearer material choice and specification, but your decking provider should be able to provide all this info to you before you commit to buying.


The site you plan to install your decking on must be free draining or have a gradient of 1 in 100 (1%) which is equivalent to 10mm of fall for every 1m of deck) to allow water to run off otherwise there is a high risk of damp and mould build up beneath the deck. Never install composite decking directly onto a solid surface without supporting composite decking bearers. A minimum airflow and drainage gap beneath the deck is crucial to its longevity.

How Dura Composites can help

If you’re still not sure what composite decking supports you need to invest in for your decking project then our Technical Sales team would be happy to help advise you.

screw decking framework