When installing your composite decking, you can put the decking on wooden joists. These joists will serve as the base on which the decks will be laid and attached.

A joist is a plank or a shaft that is usually made of timber and cut into shape. 

They are mostly used to build the structure of a house, and they serve as a base on which the roofs are laid.

Wooden joists are good for constructing the substructure or the frame on which composite decks are laid. 

They provide a reliable base for your composite deck if they are appropriately situated and properly treated.

That is why it is suggested that you should utilize composite joists to erect the structure on which you will put your decks.

 In addition, it is suggested that the size of the wooden planks that will serve as the frame of your composite decks should be 4×2.

This will give you a very strong wooden structure that will support your decks.

Building Plastic-Wood Decks

Constructing the frame that you will place your composite decking on is an important task and should be done with high-quality materials. 

The materials that you need here are the woods that will serve as the joists and woods for the pillars on which you will attach the joists. Also, you need screws to attach the wood joists to one another. 

1 Set the Foundation

This should be done after you have drawn out your plan and mark the location that you will sink the pillars that will serve as the foundation.

You need to dig the spots and place the pillars deep in them. 

The pillars can be woods that have been treated and strong enough to support the joists.

Make sure that the foundation is deep enough so that you will get a good base for the structure. 

Then, concrete should be poured inside the holes and left to dry. When the concrete is dried, and the pillar is strong, you can start attaching the joists to the pillars. 

building joist

2 Build the Joists 

To build the structure, you have to attach the joists to the pillars with screws or nails.

The joists should be laid in such a way that they slope gradually away from the house. This is important because it makes the top of your decks to slope when you have finished it. 

The usefulness of this is that rainwater will not settle on your deck, but will run off the deck.

When constructing the joists, the space between them should not be more than 300mm. This is the recommended distance for composite decks installation

If you cut the joists, you will need to paint the top with preservatives to protect it.

Also, you have to reinforce the top of the joists with joist tape so that it will not absorb water and rot.

3 Put the Composite Decking on the Wooden Joists

Putting the composite decking on the wooden joist is an important but easy task that will not take your time.

Since the joists are laid lengthwise from your house, you have to lay the decks so that they will be perpendicular to the joists. 

The best place to start installing your composite decks is from the side of your house.

Place the first set of decks and fix them down with starter clips if you are using hidden fasteners or with screws if you are using surface fasteners.

It is crucial to know that there must be sufficient spaces between the joists where two edges meet so as to accommodate the expansion and contraction of the deck.

This is crucial if you don’t want your composite deck to wrap when they expand. 

The remaining deck should be installed with the intermediate clips and screws or with only screws if you are using the surface fastening.

The deck should slope after you have finished it so that there won’t be drainage issues.

building the wooden joist
completed decking job

4 Finish the Decking

When the decks have been laid on the planks and everything is set, you can finish the edges with wood trim so that they will look good. The edges can be painted if you don’t want to use wood to cover them.


Composite decking can be placed on wooden joists when constructing a decking. You must make sure that the joists that you use are pressure-treated joists and that the foundation of the decking is strong enough to hold the decks.