Digging out clay to replace with deck.

[hopetown]

I'm planning to dig out clay backyard to replace with decking.

How deep do you think I need to go? 600mm?

Also, house extension (near planned excavation) is on a concrete slab.

Anything I need to be aware of as to not undermine foundation?

Any advice welcome.

Thank you.

[Don't believe the Hype]

Bearer Depth + joist depth + decking board depthn+ 100mm - 200mm

make sure you have fall on the clay under the deck running away from the house... you don't want water pooling under the deck when it rains or flowing back towards the house.

[AlFa]

Probably min you can get away is 200mm which would consist of 140mm bearer, 18mm decking and post just barely sticking out. Joist will be sitting between bearer on joist hangers.