Can You Put Composite Decking on Wooden Joists?

M. John
Composite decking on wooden joist

When installing ultra decking, you can put the decking on a joist. The joist will serve as a base on which you can lay your decking. If you want to build a wooden decking, you can use wooden joists.  What about composite decking? Can you put composite decking on a wooden joist?

What is a Joist?

Joists are horizontal shafts that make up the frame that supports the decking. The joist functions as a support for the decking, ensuring that its weight is evenly distributed. When constructing a decking, you have to place the decking on the joist.  You also have to use a good plank in building the joist. Remember that the joist is what supports the decking.

Can You Put Composite Decking on Wooden Joists?

So, if you don’t use good wood material in making the joist, the decking will collapse over time. Always go for a type of wood that is resistant to the elements. Pressure-treated wood and hardwood are good kinds of wood you can use.

Can You Put Composite Decking on Wooden Joists?

If you want to install a composite decking, you can put the composite decking on wooden joists. Wooden joists can provide reliable support for composite deckings if it is properly placed. When building a joist for your composite decking, it is vital to use quality wood material.

In addition, you also have to ensure that the joist is properly placed. The joist must be of equal height; one part of the wooden joist should not be taller or shorter than the others. Apart from that, you should also ensure that the joist is spaced accurately.

How to Install Composite Decking on Joists

Step 1- Lay the Foundation

First, before putting the composite decking on a wooden joist, you need to draw a plan. The plan will guide you when laying the foundation. Using the plan as a guide, mark out the area where you will place the foundation pillars. After that, dig a hole in the area you have marked to place the pillars.

You should ensure that the hole of the pillar is deep enough for good grip and balance. Then place the wooden pillar into the hole and use concrete to fill the hole. The concrete will provide a strong grip and prevent the pillars from wriggling.

Step 2 – Assemble the Joists 

Secondly, as soon as the concrete is dry, start attaching the joist to the pillars. You can make use of fasteners like a nail screw to attach it. It is important to note that when building the joist, the gaps between the joist should be above 300 mm.

Apart from that, you should lay the joist in such a way that water can flow away from it easily. It will prevent the accumulation of water when it rains. In addition, if you cut the wooden joist, you should place joist tape over the cut area to prevent the wood from absorbing water.  You can also coat the cut area with paint.

Step 3 – Put the Composite Decking on the Wooden Joists

Finally, when putting the composite decking on the wooden joist, lay it so that it is perpendicular to the joists. The decking should also slope a little to allow rainwater to flow easily.  It is advisable to start putting the composite decking on the wooden joist from the wall.

Apart from that, ensure that there is a gap of at least 5 mm between the composite decking to allow for expansion. The gaps will also prevent the composite decking from warping. After installing the decking, you can paint the edges for a finished look. If you don’t want to paint the edges, you can frame the decking if you wish.


You can put composite decking on a wooden joist. However, when building a wooden joist for your decking, it is important to use quality woods.

Tags: decking joists, joist spacing

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