I have a 20m2 deck to build. I have 3 bearers each having 3 supports. The deck does not support any load other than the deck itself. Allan Staines book says I need each hole to be 450x450x600 ? My ground is clay and shale (very hard). Is it absolutely necessary to have such big holes or would a 350x350x500 would do ?
Thanks in advance for any feedback