5 inch reinforced concrete slab - no sub-base

Hi You should always excavate for a sub base, normally 150/200mm if well compacted mot type1 or crushed concrete, depending on ground conditions then construct the raft foundation , hope this helps

It all depends on the ground type and the weight being applied. A raft foundation or large slab is designed to effectively float above weak ground and spread the load over a larger area. But theres a difference between soil and load bearing ground. Soil usually contains grass and vegetation and is roughly the top 100-250mm. In all situations as an absolute minimum the top soil should be removed to expose the load bearing ground that sits below. Its good practice when pouring concrete to provide a hardcore subbase which has been mechanically compacted. Hope this helps Nathan @ Revo