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Timber or Steel Decking Support?

December 1, 2019

One of the most important decisions to make with any new deck project is whether to use timber substrates or a steel frame to support the decking. While both are viable options, there are few considerations to take into account about the properties of timber and steel and how it will affect your decking.

Timber or Steel?

Timber on Timber

At Timber Decking Supply Shed, we recommend using timber joists as the base for your decking. Timber is a natural product, and because of this will move, expand and contract in different weather conditions. Using the same material for the decking and the base ensures that the entire structure will react to the environment in the same way, greatly decreasing the amount of stress placed on the boards.

Timber on Steel?

Securing your timber boards to steel joists can create unwanted stress on your decking. Steel is much less sensitive to the environment, and expands and contracts at different rates to timber. This can mean additional pressure on the fasteners and potentially the decking itself, causing problems such as splitting of the boards over time.

The Best Way to use Steel

While using an entirely steel frame is not recommended, steel can still be used to strengthen your decking – especially for larger or elevated decking. We recommend attaching timber joists to steel bearers, and then attaching the decking boards to the timber base. This allows you to take advantage of the strength of steel without compromising your decking down the line.

Recommended Substrate Timbers


The ‘H’ stands for hazard, and categorises the treatment applied to the timber for long-term resistance against decay, insects and other wood destroying organisms. Our H3 treated pine timbers are suitable for use outdoors and above-ground.


H4 treated pine is also insect and decay resistant, but to a higher level. This is because H4 is suitable for outdoor use with in-ground contact, meaning moisture and insects are a bigger risk. The H treatments ensure that the timber will outlive many naturally durable timbers in exposed conditions.


The ‘F’ rating refers to strength – the higher the number, the stronger the timber is. Bearings and joists for decking should be rated at least F7. We offer a number of F7 timbers, and strongly recommend treated pine, which is commonly used for outdoor projects with large structural requirements such as decks, pergolas, gazebos and more.

Find out More

At Timber Decking Supply Shed we supply all the timber you will need to complete your decking, and keep it looking its best for as long as possible. We also stock laminated engineered posts and beams to compliment all aspects of your lifestyle structure.

If you have any questions about the right timber for your Perth decking substrates or would like more information, contact us or give us a call on 08 9454 9991.