Foundations will need to be dug and because conservatories are lightweight in structure, their foundation loads are usually quite low. This can often lead to the notion that shallow foundations are satisfactory however, shallow foundations are more susceptible to subsidence.
Conservatories that are built with foundations shallower than the Building Regulations advise, are likely to encounter problems.
Building Regulations state:
A2. The building shall be constructed so that ground movement caused by :-
(a) swelling, shrinkage or freezing of the subsoil; or
(b) land-slip or subsidence (other than subsidence arising from shrinkage), in so far as the risk can be reasonably foreseen, will not impair the stability of any part of the building