I am planning to locate a hot tub weighing about 1500 kg, when full of water and people, on an area of decking. My question is, how should I go about supporting the decking for this weight. The tub is 7ft x 5ft and I had planned to support it on wood posts (100mm sq) , concreted into the ground at a depth of 18ins. The ground is quite hard clay. I thought about using 12 posts, (4 x 3 matrix) double joisted on either side of the posts and then further joists and noggins in between. The joists would be 50 x 150 mm. What are yout thoughts ?. The alternative is laying a concrete foundation and sitting the tub on this foundation and then building the deck around the tub.