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PPS 7 (Addendum): Residential Extensions and Alterations
Annex A: Residential Amenity: Overshadowing/Loss of Light

A32 Sunlight and daylight are valued elements in a good quality living environment. Effective daylighting can reduce the need for electric lighting, while sunlight can contribute towards meeting some of the heating requirements of our homes through passive solar heating. In designing a new extension or alteration to a residential property care should be taken to safeguard access to sunlight and daylight currently enjoyed by adjoining residential properties.
A33 Where an extension is poorly sited or badly designed it can cast a shadow that may reduce a neighbour’s daylight and adversely affect their amenity to an unacceptable level. It is important, therefore, that every effort should be made to avoid or minimise the potential for overshadowing to a neighbour when drawing up plans for an extension.  Overshadowing to a garden area on its own will rarely constitute sufficient grounds to justify a refusal of permission.
A34 In terms of daylighting, the effect on all rooms, apart from halls, landings, bathrooms and utility rooms will be considered. Where an extension would be likely to reduce the amount of light entering the window of a room, other than those indicated above, to an unreasonable degree, planning permission is likely to be refused.
A35 Significant problems of sunlight or daylight loss are most likely to occur in terraced or semi-detached housing situations and it is here that most care needs to be taken. An extension should be kept as far as possible from neighbouring windows and boundaries to minimise impact.
A36 To help assess the loss of light as a result of a proposed development to the front or rear of a residential property, the 60 degree and 45 degree lines, as shown in Figure 1 for single storey and two storey extensions respectively, will be employed. These lines will be taken from the centre of the closest neighbouring window. It should be noted that where the closest window is located at first floor level it may be more appropriate to consider this against the 60 degree line. The elevations and outline plans of adjoining properties should be shown on drawings, accurately scaled (in metric measurement) to allow proper consideration of this matter.
A37 The guidance in Figure 1 is not however a rigid standard which must be met in every case. Rather it is an assessment tool which will be used in conjunction with other relevant factors in order to gauge the acceptability of proposals in terms of the overshadowing / loss of light impact upon neighbouring properties. Other relevant factors which will be considered in this assessment are set out below:
  • The existing form and type of extension prevalent in the area.
    For example, where the majority of dwellings in a terrace have already been extended in a similar way to the application proposal this matter will be balanced against any adverse impact on neighbouring properties.
  • The proposed design of the extension or alteration.
    For example, where a proposed extension incorporates significant glazing in the design, the impact on neighbouring properties may be acceptable in circumstances where alternatives might result in unacceptable overshadowing.
  • The particular characteristics of the site and its context.
    For example, where daylighting to an adjacent dwelling is already impeded by an existing building or boundary wall and the proposal would not significantly exacerbate the existing situation.
  • The orientation and position of a neighbour’s window in relation to the proposed extension, the room it serves and whether the window affected is the primary source of light for that room.
    For example, account will be taken as to whether a room affected by a proposed extension benefits from an alternative natural source of light.
  • The potential size and form of an extension allowable under permitted development.
    For example, where a proposal would not have an impact significantly greater than that of an extension allowable under permitted development rights.
  • Provision of an extension or alterations to meet the particular needs of a person with a disability.
    For example, a modest single storey extension required to meet the particular needs of the person in question will be a material consideration to be balanced against any adverse impacts on the neighbouring property. This may result in the criteria relating to daylighting and overshadowing being relaxed
.Figure 1: House Extensions - Single Storey
Figure 1: House extensions single storey
Figure 1: House Extensions - Two Storey
Figure 1: House Extensions - Two Storey
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