Slab on grade or Conventional foundations are traditional NZS 3604 type foundations that were exclusively used prior to Raft floor foundations being developed. They transfer the building loads directly into the ground through foundations excavated into good ground as opposed to distributing throughout the foundation as in a raft slab. The slab itself is rarely a structural component with the exterior foundations and Hardfill doing all the work.
Conventional foundations are good on sloping sites or where the floor level is at least 1.0 m above finished Ground Level. The benefits of Raft foundations are making Traditional, conventional foundations less popular.