In this respect, there are two broad functions a wall needs to perform.
It should resist moisture from the ground and therefore would normally need damp proof courses to do so. It should also be able to adequately resist the penetration of weather from the outside to the inside of the building.
Brickwork generally gives good weather resistance on its own.
However blockwork will normally require rendering to the outside, the thickness will vary depending on the type of block used, but the minimum thickness is about 16mm.
Disclaimer - Wales
This is an introductory guide and is not a definitive source of legal information. This guidance relates to the planning regime for Wales. Policy in England may differ. If in doubt contact your Local Planning Authority.