How to Build a Base for your Decking

Posted by Kerry Wilson on

How to Build a Base for your Decking

So, you’ve worked out where your new deck is going and how big it needs to be and you’ve chosen the colour of your Composite Decking Boards. Next step is building the base.

If the site is level, a simple, ground-level deck is the easiest to construct and lay – no need for steps or railings.  If the area is sloped then you’ll need to create a raised deck – a more challenging DIY project with support joists, stairs and probably a ballustrade.  Whichever one you choose, the base structure will depend on how you’re laying the decking boards.

For a traditional deck, built for residential use with no special, heavy additions (such as a hot tub) planned, supporting joists should be no more than 400mm apart.

Decks in commercial settings should have the joists closer together – 300 to 350mm apart.

NOTE: The distance between joists is measure from centre to centre


If you’re laying your decking boards diagonally, they should be 200mm apart.

For more elaborate patterns a grid pattern may be required.


Whichever design you choose, where two boards join end to end you’ll need a double joist.  This could be an off-cut fixed to a joist or a complete joist spanning the entire deck.  The main thing is to plan the pattern before you start.

TOP TIP: You can minimise wastage by working with the size of the decking boards. If your boards are 3.6m long, a 3.6m wide deck will mean no waste at all.  Making the deck 3.5m wide means you’ll be cutting bits off and throwing them away.  And if the extra width is made up by cutting boards in half, thirds or even quarters – again there’ll be no waste.