Composite Deck

Can You Put Composite Decking on Wooden Joists?

Composite decking requires joists because they provide strength and stability. Joists are used to provide a subframe for your composite decking, gently raising the decking boards off the ground and ensuring a flat completed deck area. 

Joists are connected together in a grid-like pattern, and decking planks are fastened to the joists using a concealed fastening system. It is entirely up to you whether to use wooden or composite joists to complete your project. However, there are several factors to consider when deciding to install composite decking on wooden joists. 

As we all know, composite material lasts longer than wood since it is more resistant to the weather. As a result, with proper maintenance, your composite decking may endure for decades. Your wooden joists may live less years than the composite decking boards.

It is vital to know that your timber joists will decay and deform before your composite decking boards need replacement. Even if your composite decking boards are still in good shape, you will need to replace your wooden joists and remove them. This is, of course, very inconvenient, time-consuming, and expensive.

This is why it is suggested to utilise composite joists when installing composite decking since their lifetime will be the same and they will be less prone to moisture damage, such as rot.

We recognise that composite joists are more expensive than wooden joists, however picking wooden joists will cost you more over the long run. 

If you still decide to go with wooden joists due to price constraints, be sure to choose pressure-treated wood, since it will last longer than non-treated wood.

Pressure-treated wood has been bathed in chemicals to extend its life and prevent rotting and insect infestation. Although treated wood lasts longer than untreated wood, it does not have the same longevity as composite joists, and you will still need to replace your joists before your decking reaches its full lifespan. 

Overall, yes, you can install composite decking on top of wooden joists; however, this is not encouraged and may create problems in the future.

If you have an existing wood subframe that has been standing for years and are only looking to replace your decking, it is not recommended to install brand new composite decking on an existing wooden frame because it will lose the structural integrity required to stabilise the decking for decades to come.

A Simple Step-by-Step Guide for Building a Wooden Subframe:

Constructing the structure on which to lay your composite decking is a critical operation that should be accomplished using high-quality materials. 

You should only try to build a subframe if you have prior experience, since it is risky and should be done with care and safety. If you have no expertise, it is best to employ a deck builder.

First, sketch up your layout and note the position where you will dig the posts to support your joists.

Once marked, dig into the areas and insert the posts deep into them. As a general guideline, your posts should be drilled underground at around one-third of their height. The posts may be constructed of treated wood, which is sturdy enough to hold the joists. 

Then, concrete should be poured into the holes and allowed to cure. Once the concrete is dry and the poles are in place, you may begin connecting the joists to them.

To construct the structure, join the joists to the pillars using screws or nails. The joists should be set such that they slope progressively away from the house. This ensures that rainfall does not collect on your deck and instead runs off.

When building the joists, the distance between them should not exceed 300mm. 

If you trim the joists, you must paint the top with preservatives to preserve it. You should also strengthen the tops of the joists using joist tape to prevent them from absorbing water and rotting.

Your joists should be put in a grid-like pattern to provide the decking boards on top optimal strength. Once everything is bolted together and secure, you can start laying the decking boards on top.

 Because the joists are set longitudinally from your home, you must align the decking planks perpendicular to the joists. Laying the decking boards from the outside in.

Use starter clips to secure the first set of decking boards around the edge, then concealed fasteners for the remaining boards. Screw the clips into the joists underneath, not the decking board itself. This will result in a flush surface finish. 

It is critical to understand that there must be enough room between the joists where the two sides meet to allow for expansion and contraction of the decking while avoiding damage.

As previously said, your decking surface should slope once you complete to prevent drainage difficulties. Pooling water on your surface will harm your decking planks. 

If you have any question relating to the composite decking build or the joists builder, talk to our composite decking build team in melbourne anytime.