B5.1.1 Scale, massing and proportion of residential extensions

Code: 5.1c

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: 5.27c 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.

Code: 5.2c

Residential extensions in the Green Belt must remain proportionate over and above the size of the original house. For extensions to be proportionate, the total of all extensions must be a maximum of up to 50% of the volume and 50% of the floor space of the original house. The ‘original’ house means the house as it existed on 1 July 1948 or, for properties built after this date, as first constructed.

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 all existing and proposed extensions)
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 all existing and proposed extensions)
a percentage increase must be drawn from these calculations over and above the original house
where any building that is an extension to the original dwelling is proposed to be demolished, the floor space and volume of the demolished building can be offset against the proposed extension

The diagram shows two ground floor plans of a singular home. One shows the existing ground floor plan in blue and the other shows an example of a proposed extension attached to the existing ground floor plan in orange.

Figure 131: Shows an example floor plan with measurements which note the original floorspace, and total acceptable extension (Code: 5.2c)

Example: Calculating floor space

If the floor space can be increased by 50%, this means up to 20m² of extra space is allowed. Since the planned total extensions are only 12 m², they are within the limit.

Relevant equation: Length x Width = Area (m²)

The diagram shows the same home but in 3-D form again with two parts. One in blue for the existing home and orange for an example of a proposed extentsion to demonstrate the additional massing and size of the home in a plan format to enable assessments.

Figure 132: Shows an example 3D line drawing with measurements which note the original volume of a property, and total acceptable extension (Code: 5.2c)

Example: Calculating volume:

If the volume of the house can be increased by 50%, that means up to 125m³ of extra volume is allowed. Since the total extensions are only 48 m³, they are within the limit.

Relevant equations:

roof: (Length × Width × Height) ÷ 2 = Roof Volume (m³)
house: Length × Width × Height = House Volume (m³)
total: Roof Volume + House Volume = Building Volume (m³)

Code: 5.3c

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 vehicular access over a footway or verge, which involves a S184 agreement with the Council’s Highway Authority as required.

Code: 5.4c

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 in this instance.

Exceptions:

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

Guidance: 5.5g

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

Guidance: 5.6g

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.

3-D model sketch of a single plot with a 2-storey house. A 1.5 storey extension is highlighted in orange to the right hand side of the house.

Figure 133: Shows a side extension less than two-thirds of the original property width (Guidance: 5.6g)

Guidance: 5.7g

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

A diagram of two semi-detached homes in an identical green facing wall and grey roof with a black and grey front door/porch, a large bay window and two upper floor windows. Each semi-detached home shows an attached side extension designs shown in a contrasting orange and grey colour.

Figure 134: Shows acceptable (left) and unacceptable (right) extensions in relation to the balance and proportion of the original property (Guidance: 5.7g). The left example maintains alignment of windows and rooflines, while the right disrupts them with mismatched roof form and window proportions

Guidance: 5.8g

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.

3-D model sketch of a single plot with a 2-storey house. A 1 storey extension is highlighted in orange to the rear of the house.

Figure 135: Shows a rear extension no more than two storeys in height that retains 50% of the original garden (Guidance: 5.8g and 5.9g)

Interior of a single storey extension with kitchen units and wooden flooring, also a roof light is shown in the white ceiling. The rear wall of the extension is mostly glazed.

Figure 136: Shows an internal single storey rear extension with an additional central rooflight (Guidance: 5.8g). Image and architectural design provided by Hampton Design Contractors

Interior of a single storey extension with kitchen units and white wooden flooring, also roof lights in shown in the white ceiling. The rear wall of the extension is mostly glazed with views of the back garden.

Figure 137: Shows an internal single storey rear extension with a vaulted roof and glazed gable (Guidance: 5.8g). Image and architectural design provided by Hampton Design Contractors

Guidance: 5.9g

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.