What Is A Decking Subframe?

April 2022
Anton White

A decking subframe is the structure used to support your decking area. They are made up of joists that support the decking at regular intervals, along with a way to support the joists of the ground.  However, there are a few main different materials used for these, and in the article I will go over the main materials used, as well as a few benefits and drawbacks of each.

The three main materials that are used are as follows:

  • Wood
  • Composite/ Plastic
  • Aluminium


Subframe Material #1 – Wooden

Wooden subframes for decking, both composite and wooden decks, have been around for the longest, and is usually the most well-known. Timber is easy to work with so many landscapers and DIYers use it for building.

The biggest issue with using wood for the subframe is its lifespan. Timber subframes only last from 5-10 years before they need replaced. The main reason that this is the case is because it is very susceptible to water damage.

Water makes timber rot, especially in places where there are two materials in contact. i.e., in between the deckboard and the joist. There are ways to prolong the lifespan of the timber and stop water rotting it so quickly, such as coating the joists and decking in anti-rot or using deck tape in between the boards and the joists, but inevitably, it will still warp and rot over time.

The main benefit of using a wooden subframe is its initial upfront cost. It is usually the cheapest initially, so the initial invest is not as high. However, after 5 – 10 years it will need replacing, doubling the subframe cost over 10 years or so.


Subframe Material #2 – Plastic/Composite

Plastic or composite decking subframes are a relatively new innovation and are used to replace timber decking areas. The joists are made from either entirely plastic, or a wood and plastic composite, a bit like the actual deck boards themselves.

The main issue with plastic or composite joists is the fact that they are affected by water. Not in the same way is timber – they won’t rot – however they will still expand and contract due to the absorption of water. This can mean that over a larger area, the joists will get longer and shorter, depending on the dampness of the area. This is especially an issue where joists are in-between a building or on a terrace. The main reason for this is that when the joists press up against a wall or hard object on both sides, it will warp, making your deck bow in one way or another. This will likely give your decking area a ‘bouncy’ feel, and it may move up and down.

A great benefit of composite joists is the fact that they wont rot like timber. This means that the actual joist lifespan is longer than that of wood, however the joists may bow or warp in the meantime.


Subframe Material #3 – Aluminium

Aluminium subframes are another alternative. An in many peoples opinion, including mine, is the best option in terms of ensuring your deck lasts as long as possible, and remains in its original state – looking as good as new!

One benefit of aluminium subframes is the fact that they will not warp and will hardly expand and contract at all. This is because it is not affected by water – it won’t rust – or affected by heat badly – the expensive and contraction is minimal.

Like timber and composite, it is a relatively easy to work with, and the only difference is that all connectors are used to connect all joists, whether a corner or a straight connection. It is very simple to screw, using a self-tapping screw which most suppliers of the joist will also supply.

The only one drawback of aluminium subframes is that initially, their upfront cost can be more than that of composite and wooden joists. This is due to the fact that it is a far superior product with a longer lifespan.

However, over time the investment pays off. This is because whilst wooden subframes will need replaced, the aluminium subframes will still be going strong (assuming it is installed correctly) 

The below diagram gives a visual indication of the different elements of the materials. 5 being ‘good for’ and 1 being ‘bad for’.




What Next?

Now that you've read more about the different types of subframe, you may begin thinking about using an aluminium subframe an option for your garden or balcony. We know that it can get confusing working out quantities, so why not give us a call or an email so that we can help you out?

Also, seeing as you are looking at subframes, we’re sure you must be looking for the decking!? If so, we do have a large range, and would be very happy to send samples help you with a quote if it would help.

You can also call us on 0208 159 2999 or send us an email to sales@ovaeda.com to get quotes, guidance, and any technical support with your plans. If you think you will require the help of a professional installer, we are happy to recommend one to assist.