CLASS G:- The installation, alteration or replacement of a chimney, flue or soil and vent pipe on a dwellinghouse.

To you and I this means chimneys, soil and vent pipes and other flues for heat producing appliances.  There will be exceptions but this is what it means to most people and extension projects.

The Legislation breaks this down into several classifications that at first hand appear fairly generous but it is not until you read the restrictions, it becomes clear that there are some very definitive constraints. 

The Governments approach in their wording is to tell you with a very 'broad brush' what your are allowed to build & then want to install the 'masking tape' to define the areas where the 'broad brush' can only be applied.

We will not repeat the wording of PD legislation here as you can read it for yourself elsewhere on this web site. 

Most extension work under class A & B for example will normally include the alteration or installation of a new chimney or svp.

It is this Class G where most normal works to these external items are allowed within certain dimensional limits and site zoning of the dwelling (eg conservation Area).