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What should I know about deck joists?


Whilst you might have given a great deal of thought to your choice of deck boards and other elements such as balustrades, fixings and lighting, you might not have thought about deck joists.

Whilst these bits of timber cannot be seen once your deck is complete, they are perhaps more important than your deck boards! Deck joists give you the framework to attach your timber decking boards to and play a very important part in ascertaining the strength and durability of your decking. If you skimp on this part of the project you stand to compromise its service life, regardless of the quality of the deck boards. You can also create a safety issue and so it is important to get it right.

The first factor to consider with deck joists is whether they should be treated to Use Class 3 or 4. It’s quite simple to determine. If the joists will come into contact with the ground, they should be treated to Use Class 4. If however, your decking is to be raised and the deck joists will remain above the ground, Use Class 3 is appropriate.

Having determined the level of preservative treatment required, consider the size of joists that you need. This should correlate to a number of factors including the weight bearing that is required and whether the deck joists will sit directly on the ground or be raised. If you are using professional help, your installer will be able to specify the size of deck joists that you require. Alternatively, many of our TDCA approved suppliers will be able to offer you guidance on sight of your decking plan, helping you to specify the optimum timber for your project.

If you have any specific queries about deck joists, please do get in touch with the TDCA and we will be happy to help you.