Most but not all conservatories will sit quite happily on a simple concrete slab base that will serve both as a foundation and floor structure. If the ground is covered by a deep layer of topsoil it will be better to dig trench foundations down into the natural subsoil. Even with foundations under your walls you will still need to support the floor slab on a sound base and the construction of a conservatory is no different in this. Ground-bearing conservatory bases are usually in the region of 100mm thick and are cast over a level bed of hardcore. For the concrete base to function properly it must be carefully formed and there are several key elements to its design and construction.