Elevated decks will require decking posts sinking into the ground. This is no easy task and can be back breaking, especially if you have lots of holes to dig.

Special care must be taken when digging out the holes for the decking posts as services such as gas, electric or water could be buried underneath the soil or storm water drain or soil pipes. The post holes need to be 700mm deep and the decking posts are 100mm*100mm treated timber.

deck post positions

The deck post holes need marking out. This can be difficult and can be made easier if you use some of the joists and put them into position. For the deck in this project we are spacing the joists at 400mm centre's. The decking posts need to be spaced at every metre in each direction. We have marked this onto the ledger and will temporarily screw a joist into position until we have marked the correct place for the post hole.

deck posts in position

Here we are working on the top tier deck and have temporarily screwed the joist into position so that we know exactly where the holes need to be. Once the holes are marked you can remove the joists and start digging. The joists can be replaced when you are ready to fix the post in position.

post holes dug out

Here we have dug out several post holes. The post holes need to be 700mm deep and the decking posts are 100mm*100mm treated timber. Digging these holes is not easy and the smaller the hole is the less materials needed to fill it in afterwards.

brick in post hole

At the bottom of the hole place half of a medium density block. The builders merchants had sold out of these and so we are using two engineering bricks placed on their sides. screw the joist back into position and then Position the post and level it using a spirit level. It is best of one person now holds the post and ensures that it stays level whilst the hole is packed.

pack hole with masonry

Filling a hole this size with concrete or postcrete / postfix would be very expensive and unnecessary and so we are using some broken up concrete to pack the post out a little. Hold the post straight whilst packing out the hole.

fill hole with gravel

Now we have emptied a bag of gravel into the hole, this will fill the gaps between the pieces of concrete that we put in the hole first.


Now it is time to add a couple of bags of postcrete. There are several different brands of this and they do vary in quality a little . The beauty of these products is that they set in about 15 min's and so they do not stop you working. You can use concrete if you like, but it will take hours to set fully. When the postcrete is in the hole pour water over it and it will start to cure!

cut deck post

When the posts are secured you can mark the top of the joists on the posts and then cut the post off slightly below this level. A reciprocating saw makes light work of this!

deck posts in position

Here you can see that the decking posts have been secured and they have been cut to length and the cut ends have been treated. Now the joists can be fastened to the posts.

deck posts in position

Where possible the base of the post needs to be raised so that water will not collect at the base and rot the wood. This is easy to do and can be achieved by using more postcrete than necessary in order to make a small mound at the base of the post.