The impacts-based approach

The proposed new regime aims to replace the existing complex system of using percentages and volumes to calculate allowances for domestic extensions with straightforward rules and clear dimensions.

It should provide extra freedom for permitted development so long as developments have little or no impact beyond the host property. As a result the need for householders to submit planning applications for many minor projects would be removed.

The impacts of domestic developments on adjoining properties which the proposed new regime takes into account include:

• overlooking – loss of privacy
• overshadowing – loss of daylight

In most cases these impacts are measured quantitatively and the proposed permitted development regime is expressed in terms of heights, distances and other clear measurements and limits.

Wider impacts are those which affect the character and appearance of the immediate street scene. These impacts are measured qualitatively rather than quantitatively and are therefore more subjective than those listed above.

Another broader set of possible impacts which the proposed regime takes into account are:

• harm to designated areas such as conservation areas or Areas of Outstanding Natural Beauty
• harm to listed buildings
• harm through the cumulative impact of a number of small developments – e.g. water drainage capacity in an area being adversely affected by the building of a large number of concrete hard surfaces