The key to constructing firm, long lasting decking is in building the frame correctly.

Building the Decking Frame

The best way to avoid errors when building your sub-frame is to lay the pieces out in your garden as they will be constructed. First lay out the outer joists, remembering to allow for overlapping at the corners. Then cut your inner joists to the right size and position them inside the frame. The inner joists need to be laid in the opposite direction in which the decking boards are to run in order to allow them to be attached securely.

The inner joists should be no more than 4 metres apart to avoid contravening planning laws, so use tape measure to mark off 4 metre intervals along your outer joists, marking both sides of the frame to ensure that the inner joists are level.

You should then check that your decking frame is square by measuring across the diagonal and ensuring that the two measurements are the same. Once you are happy, then you can start screwing the decking frame together, starting with the outer joists and using countersunk coach screws.

Building a Decking Frame on Wet Ground

You may notice that some areas of your garden are prone to damp and/or water-logging, in which case you should raise your decking off the ground using concrete blocks to prevent wood rot from damaging your decking frame.

Once your site has been cleared, dig a series of small holes around 15cm square and 15cm in depth around the edge of the deck. These should be spaced a metre apart.

Fill each hole with concrete, allowing about 6cm of concrete to project out of the hole. Before the concrete dries, level off the top of the concrete blocks to keep each one level.

Once the concrete blocks are fully dried, cover the area to be decked with building membrane, and cut around the concrete blocks to allow them to show through. Keep the cut-outs ready to place on top of the concrete posts when you put the decking frame in to place. Cover the building membrane with gravel to help prevent weeds from growing through.

Check out these pages for more information on installing your own decking:

How to Build a Timber Deck

Timber Deck Ideas

Build a Simple Square Deck

This video also contains some useful tip and a visual demonstration on how to install your own decking: