B5.1.1 Scale, massing and proportion of extensions

Residential extensions must remain subordinate and proportionate to the original building in both scale and form by ensuring that:

• all extensions step down by at least 0.5 metres from the roofline of the original building

• side extensions are also set back a minimum of 0.5 metres from the front elevation of the original building

• a minimum 1 metre gap is maintained between the extension and the side boundary of the plot to allow for access, enable future maintenance and prevent a ‘terracing effect’

• all proposed extensions must not result in an increase in surface water run-off, and any loss of permeable ground must be mitigated

• any extension or alteration must maintain adequate access to existing drainage and new drainage must be well integrated

• extension proposals must also prevent excessive overshadowing of habitable rooms of neighbouring properties and maintain a good relationship between existing buildings and avoid over-bearing impacts on adjacent properties and amenity areas, taking into account Code: C5.10 as required.

Exception: Deviation from these standards may be acceptable where a proposal clearly responds to the unique characteristics of the site or local context. Any such proposals will be considered by the Council on a case-by-case basis.

Residential extensions in the Green Belt must remain proportionate over and above the size of the original house. A proportionate extension must, at its maximum, be up to 50% of the volume and 50% of the floor space of the original house.

To achieve this, applicants must:

• measure the floor space using the external overall width and length measurements of the house (this method is used to calculate the floor space of both the original house and the proposed extension)

• measure the volume by using the external overall width, length, and height of the house which includes all internal spaces, both living areas and voids (this method is used to calculate the volume of both the original house and the proposed extension)

• a percentage increase must be drawn from these calculations over and above the original house

• where any buildings are to be demolished as part of the proposals, the floor space and volume of the demolished building can be offset against the proposed extension

Where an extension or alteration affects existing parking (whether by increasing demand or reducing current provision), it must include an updated parking layout, clearly shown on the submitted plans. This must demonstrate how the scheme complies with the minimum parking standards as set out in District-Wide Cycle and Other Parking Standards (Appendix 7).

Note that whilst permitted development rights allow for some parking-related improvements, it is crucial to check the specific rules and regulations related to your home and the proposed development with the Council. (For example permitted development rights do not apply to works on a public highway). Section 184 of the Highways Act outlines the process for obtaining permission for vehicles access over a footway or verge, which involves a S184 agreement with the Council’s Highway Authority as required.

Front extensions often upset building lines and architectural rhythms, and appear unduly prominent in the streetscape, especially where a row of properties has a uniform character. Therefore extensions at the front of a property must be avoided be avoided in this instance.

Exception:

• Front extensions may be acceptable where all of the following can be demonstrated:

  • the street does not follow a strong regular pattern

  • the house is well set back from the street

  • the proposal is sympathetic to the original house and immediate local character

• When designing a front extension the following principles must be applied:

  • front extensions must be well balanced in relation to the existing house and maintain the character of the area

  • soft landscaping to the front of the house must be maintained or provided, ideally next to the pavement edge

  • extensions that face highways and public footpaths must have active frontages. This means that front doors and windows must face the street

  • the roof of the extension must be appropriately integrated with the existing property normally by using a similar pitch on the roof of the extension, and must be set down from the roofline of the original house by at least 0.5 metres

In some cases a porch can create a welcoming feel to a home and interest on what may otherwise be a blank elevation. Proposals for porches should:

• be modest in scale and reflect the style and materials of the home

• not detract from the character of the street

• reflect the roof style of the original house

Two storey, and single storey side extensions should be no more than two thirds of the width of the original building. This approach helps preserve the proportion and symmetry of semi-detached homes, in particular.

Proposed windows and doors should match the scale and proportions of the existing property and be positioned in line with the current window arrangement.

Extensions should generally be no more than two storeys in height at the rear.

Exception: Taller rear extensions may be acceptable where justified by the prevailing character or topography of the area, and where the proposals have no adverse effects on neighbouring homes.

At least 50% of the original private garden space should be retained to prevent over development and ensure sufficient amenity space for occupants. The ‘original’ garden space means the private rear garden as it existed on 1 July 1948 or, for properties built after this date, as first constructed.

Exception: This excludes any areas converted to parking, subdivided for development, or otherwise altered through land sale or acquisition.