Fence/decking posts

[notb665]

I am building an area of decking which will be 4.8 metre square. I am putting in 147x50mm joists supported by a post every 1.2 metres. The posts are 100x100mm.

To what depth and width should I dig the holes for the posts? I have tried searching but can't seem to find a definitive answer.

Any advice appreciated, thank you.

 

[2scoops0406]

Rule of thumb,about a third of the total length of the post should be underground. So for a 2 metre post above ground, a 3 metre post should be buried about 1 metre.

You can get away with less if concreted in.

 

[notb665]

Thank you very much - what about the width of the holes if I am using 100mmx100mm posts?

 

[2scoops0406]

You dont really want the hole much wider than the post, 'cos the soil is probably already nicely compacted, so say 150 - 200mm should be OK.

 

[JohnD]

If you can make a concrete or brick plinth, and put the wooden legs on that, they will not rot so quickly.