Chat with us, powered by LiveChat

Installing Timber & Plastic Joists & Posts

Installing Joists & Posts On A Soft Foundation

Whether installing plastic joists and posts or timber joists and posts ensure the area is clear and free of any obstacles including any cables and pipes.​

Installing Timber & Plastic Posts For Composite Decking

Measure and mark out the area including where holes need to be dug for posts ensuring posts are spaced every 1200mm approx. If Newel Posts are used, ensure the holes are dug in the right place.

Dig 600mm minimum holes into the ground making sure the width of the hole is at least 4 times the width of the post.

Measure and cut posts to the required height. Posts can be left a little longer and trimmed down at the end if preferred.

Place a layer of gravel into each post hole to help hold the posts in place while the levels are checked.

Pour concrete into the holes and wait to set.

We advise using a weed membrane to stop any vegetation growing. Roll the membrane out over the area and cut to size. Gravel or pegs can be used to hold into place.

Check all dimensions including outer board dimensions allowing any space for Newel Posts where required.​

Installing Timber & Plastic Joists For Composite Decking

Measure and mark the height of the deck taking into account the deck boards. We advice creating a decline of 1% – 1.5% away from a property acting as a drainage slope.

Measure and cut outer joists where required and clamp into place where marked. Pre-drill holes and screw together using 2 coach screws at each post.

Measure and cut support beams where required for underneath the outer joists. Pre-drill holes and screw together using 2 coach screws at each post.

Measure and cut inner joists where required. Pre-drill holes and screw together through the outer joists at each end at 300mm max intervals (centre to centre) using 2 coach screws. Add extra support by screwing through the inner joists and into the supporting beams.

​Leave a 10mm expansion gap between joist butt joins.

Double joist where deck boards meet at butt joins allowing a 3mm gap between joists.

​If Newel Posts are used measure and cut where required. Pre-drill holes and screw together using 2 coach screws through the outer joist and into each post. Ensure the posts are flush with the bottom of the outer joist. If numerous Newel Posts are used we recommend evenly spacing allowing access to the deck.​

Why Choose Composite?

We are the UK's leading supplier of cost effective high quality composite decking, composite cladding and composite fencing for residential and commercial projects. Our products are made to the highest possible standard and go through rigorous and in depth testing phases before, during and after manufacture. Our forward thinking experienced team deliver efficiency, quality and the best customer care at all times providing customers a hassle free end to end solution when purchasing our products.

Get in touch today to discuss your next project.


Claim your free composite decking, cladding and fencing samples now.

Browse Samples


Find out the materials required for your next project. Use our calculator and get a quote in less than 5 minutes.

Get Started

Calculate a Quote Calculate a Quote


If you have any questions regarding our Assured Composite® ranges then please give us a call on 0166 440 0140 or email us at

Contact Us