Best sub-base for raised patio

[the_new_guy]

When I go out of my back door there's a couple of steps down to an existing patio that's 80cm below the level of the house.
The plan is to build a new patio of about 24m2 over the existing one (possibly on top of, possibly remove it: suggestions?). Anyhow, do people have suggestions for the best material to use for a sub-base.

One post (from Jan-2005) had a 12"-18" deep sub-base of broken concrete. I guess that my sub-base would be about 60cm, assuming I remove the old patio slabs. Is this the best material to use to prevent settling?

Pete

[Tony McC]

You don't need to use a sub-base material for the whole 600mm, it's just wasteful. On site, we would probably use a selected fill material (depends on what's available locally) for the first 500mm (done as 3 layers, each being 170mm-ish and fully compacted before placing the next) with 100mm of genuine sub-base. Suitable selected fills would be 75mm crusher run or SF1.

You might prefer to use old flagstones, broken brick and the like, but you need to be sure there are no voids, by blinding with sand or 20mm to dust before continuing the build-up. In such a scenario, I'd be tempted to use a good geotextile between the capping layer and the 100mm sub-base, just to be sure there's no risk of trickle down and settlement.