Six things to consider before applying to extend your property in the Green Belt

PUBLISHED: 12:30 10 January 2018 | UPDATED: 17:20 10 January 2018

The pretty village of Ayot St Peter, north-west of Welwyn Garden City, is located within the Green Belt

The pretty village of Ayot St Peter, north-west of Welwyn Garden City, is located within the Green Belt


Applying to extend in the Green Belt? These are the things you should consider first, says Andrew Boothby, senior planning consultant at Aitchison Raffety

Andrew Boothby, Aitchison RaffetyAndrew Boothby, Aitchison Raffety

There are over 1.6 million hectares of Green Belt land in England of which over 13,000 hectares fall within St Albans district. The Government attaches great importance to Green Belts, stating that the fundamental aim of Green Belt policy is to prevent urban sprawl by keeping land permanently open; the essential characteristics of Green Belts are their openness and their permanence.

National planning policy states that ‘inappropriate’ development is, by definition, harmful to the Green Belt and should not be approved except in very special circumstances.

However, national policy identifies a number of exceptions which do not form ‘inappropriate’ development and these include “the extension or alteration of a building provided that it does not result in disproportionate additions over and above the size of the original building”.

Local Policy in St Albans states that residential extensions to existing dwellings in the Green Belt should be assessed on the following specific guidance:

1. The size of the extension

When calculating the size of your extension you must take into account any previous extensions that have been added to the buildingWhen calculating the size of your extension you must take into account any previous extensions that have been added to the building

In St Albans district an increase of between 90-180 cubic metres or 20-40 per cent of the dwelling’s original floor space is considered to be a proportionate addition. However, the amount you can add within these permitted ranges is determined by how well your extension performs against a list of other criteria.

2. Previous extensions

When calculating the size of your extension you must take into account any previous extensions that have been added to the building. The starting point for calculating the size of your extension is the cubic content or floor space of the dwelling when it was first built, or as it stood on July 1 1948 if it was built before
that date.

Consequently, be aware that existing extensions to your property may have already used some or potentially all of your available allowance.

3. The type of extension

Generally, single storey extensions are less harmful to openness than two storey extensions due to their smaller scale. Likewise, extensions to the rear are usually considered better than extensions to the side as they do not interfere with the gap(s) to the side of the existing house. Roof extensions which significantly raise the eaves or ridge of a property are normally seen as unacceptable; however, smaller additions such as dormer windows can be appropriate. Furthermore, extensions which significantly change the character and appearance of a dwelling are not generally supported.

Outbuildings or garages within five metres of the original building, and over 10 cubic metres in volume, are classed as an extension and therefore will take up some of your available allowance.

4. Visibility from public viewpoints

When choosing the location of your extension it is important to consider how visible it will be from public viewpoints. This includes footpaths, bridleways and highways. As stated above, rear extensions are often shielded by the original building whereas side extensions can be more prominent.

Existing screening by walls, fences and vegetation can be
taken into account; however, this alone will not hold sufficient weight to render an extension appropriate.

5. Extensions in gaps between dwellings

As set out above, extensions to the side of a property usually have a greater impact on openness, particularly if they adversely close the gap between your property and a neighbour’s.

Consequently, if you are proposing to extend to the side of your property it is important to leave a gap between your extension and the site boundary, particularly at first floor level.

6. Design

As well as complying with Green Belt guidance you must make sure that your extension achieves a high standard of design. For instance, a flat roof should not be employed purely to reduce the height or volume of an extension if it would not be in-keeping with the character and appearance of the original house.

Before embarking upon a planning application, Aitchison Raffety would be keen to provide initial informal advice so please do not hesitate to contact Andrew Boothby on 01442 874087 or via email at

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