26. Street Infill

26.1. General principles

Street infill occurs on site where there is a significant gap between the walls of existing buildings, or where an existing building makes poor use of its site, and demolition and redevelopment would achieve a greater quantity of new accommodation.

Street infill tends to occur within streets occupied by terraced houses or detached and semi-detached homes where the side walls of neighbouring properties are at an angle of less than 45 degrees from one another. Where this angle is significantly larger, this could be considered to be a “corner site”, which is covered by a separate chapter of this guidance document.

A drawing of a terrace of different heights.
Figure 98: Street infill doesn’t necessarily need to match the adjacent eaves and ridge heights
A diagram of a house with a space next to it.
Figure 99: Excessive gaps between existing houses provide an ideal opportunity for new homes whilst also enabling the streetscape to be repaired. These often occur on plots of land which are partially occupied by an existing property.
A diagram of a terrace with an empty space.
Figure 100: Gaps between existing terraced houses can also be used to deliver new homes.

26.2. New infill homes on vacant land

Where existing gaps in the streetscape allow, existing plots can be sub-divided to create space for new homes.

In figure 103, opposite, a new dwelling has been created on an area of land adjacent to an existing home. The larger plot has been separated into two to provide a rear garden for each.

The principal elevation of the new development maintains the building line established by adjacent buildings.

The rear elevation of new development should avoid extending further than a 45 degree line extending from the closest neighbouring windows (see figure 101).

When new infill development is introduced into an existing street of detached or semi-detached properties, care should be taken to respond to the rhythm of gaps between buildings. The side walls of new development should generally be offset from the boundary by the same distance is its immediate neighbour (see figure 102).

Taking into account the definition of floor levels established in paragraph 12.2.4, a new dwelling within a street of consistent height should broadly maintain the line established by neighbouring homes (see figure 104, opposite).

Where the buildings on the street have inconsistent heights, new development can generally extend to one storey taller than the tallest of its immediate neighbours (see figure 105, opposite).

A diagram of the overbearing limit for neighbouring houses.
Figure 101: 45 degree line to limit overbearing of neighbours

A diagram showing equal gaps between new and old properties.
Figure 102: New detached homes should respond to the rhythm of gaps between existing properties.
A diagram showing a single plot being divided in two for infill development.
Figure 103: A large plot occupied by a single detached dwelling can be sub-divided into two smaller plots to make way for a new infill development.
A diagram showing a road with similar house heights.
Figure 104: Where existing building heights are broadly consistent along a street, new infill development should not be significantly taller than the buildings either side of them.
A diagram showing a road with differing house heights.
Figure 105: Where existing building heights are varied, new infill development may be up to one storey taller than its neighbours, provided that it achieves a high degree of design quality.

26.3. Replacement infill development

Where existing properties sit within large plots and make poor use of the space around them, more extensive development may be preferable.

For example, single-storey detached dwellings such as bungalows usually represent an under-use of space.

In these cases, the replacement of existing buildings and a significant increase in the number of homes on a site will generally be supported where this meets all other planning policy requirements.

The replacement of a small single dwelling which under-occupies a large plot could result in three or more family homes.

A photograph of a tall thin brick building with a steep pitched roof and long projecting balconies
Figure 106: This Stirling Prize shortlisted project by architect Groupwork slots a contemporary new residential development into a narrow site on a street of varied character in Hackney. (website: www.groupwork.uk.com, photography: Groupwork)
A photograph of a large, blocky residential development.
Figure 107: Forster House in Whitefoot designed by Levitt Bernstein Architects (Website: www.levittbernstein.co.uk, Photography: RCKa)
A diagram showing how a single plot can be replaced by three new dwellings.
Figure 108: By removing a single dwelling which fails to make optimum use of its site and replacing it with new homes can deliver new family homes while repairing the streetscape.
A diagram showing a new development which conforms to the heights of existing buildings on the road.
Figure 109: In streets which have a consistent height, new development should generally follow that of its neighbours.

An alternative arrangement for a replacement infill development might include the demolition of an existing family-sized property and its replacement with apartments.

Note, however, that a net loss of family homes will not usually be supported unless there is a strong case otherwise. Wherever possible, any development of this nature should include a dwelling with at least the same number of bedrooms as the property which was removed to make way for it.

Where there is a clear prevailing roofline, new development should not be significantly taller than its neighbours, taking into account the definition of a storey to include pitched roofs.

Where new development is proposed within a street with varying character, new development that is taller than neighbouring properties may be acceptable, providing that it is of considerable quality; that the quantity of natural daylight and sunlight reaching the existing principal windows of habitable rooms are not diminished to an unacceptable degree; and that the siting of new windows, terraces or balconies do not compromise the privacy enjoyed by adjacent homes.

New development which is significantly taller than its neighbours will need to be of exceptional design quality. For the purposes of this document, “marginally taller” means up to half a storey. “Significantly taller” means half a storey or more.

An unusual tiled building with inventive fenestration.
Figure 110: Kaolin Court by Stolon Studio replaces single-storey workshops and offices with a four-storey development of new homes. The scheme employs a central courtyard which has enabled the use of the whole site. (website: www.stolon.co.uk, photography: Robert Barker)
A terrace of brick houses.
Figure 111: New homes in Crofton Park designed by Brooks Murray Architects. (website: www.brooksmurray.com, photography: RCKa)
A diagram showing how to fix a streetscape when replacing a building.
Figure 112: Excessive gaps between existing houses provide an ideal opportunity for new homes whilst also enabling the streetscape to be repaired. These often occur on plots of land which are partially occupied by an existing property. Where existing houses make poor use of space, such those which are significantly lower than their neighbours, for example, then replacement or upward extension to optimise the use of the site will be encouraged.
A diagram showing a new building with a similar height to existing ones.
Figure 113: Where the height of existing buildings is broadly consistent, new infill development should respect the prevailing height of its neighbours.
A diagram showing a new building that is taller than its neighbours, which vary in height.
Figure 114: Where a street consists of buildings with varying height and character, a new development of up to one storey taller than its neighbours is usually possible.

26.4. Infill development in terraced streets

Where gaps exist within a street of terraced houses, these are usually appropriate for new infill development providing there is sufficient width to achieve an internal layout which meets space standards (as set out in the Nationally Described Space Standards) and other planning policy requirements.

The principles of terraced infill development should follow those in this section and section 12.

The street-facing elevation of new infill development should maintain the principal building line established by adjacent buildings.

The rear elevation of new infill development should be positioned to ensure adequate natural daylight reaches the principal window of habitable rooms. Usually this means that new development should not project any further back than a 45 degree line set out from the closest edge of neighbouring windows.

New development at the end of an existing terrace, and the site is at the intersection of two roads, counts as corner development and are discussed in section 29.

In terraced streets with a broadly consistent appearance, new windows should align, where possible, with those of neighbouring properties.

A diagram showing the rules for new developments in relation to neighbouring windows
Figure 116: New development should generally project no further back than a line projected 45 degrees from a neighbouring window
A photograph of a thin contemporary brick and concrete house, between two existing terraced houses of different heights.
Figure 115: Replacing an existing two-storey coach house, this infill development by architect Selencky Parsons creates a new family home from a narrow plot. (website: www.selenckyparsons.com, photography: Richard Chivers)

A diagram showing a plot being divided in two and a new home being built on it.
Figure 117: The sub-division of an existing plot within a terraced street into two can create the opportunity for the construction of a new home.
A diagram showing a new house in a terrace that's the same height as neighbouring houses.
Figure 118: Where the height and appearance of existing buildings is broadly consistent, new infill development should respect the prevailing height of its neighbours.
A diagram showing a new house inserted into a terrace that is significantly taller than its neighbours, on a terrace where houses already vary significantly in height.
Figure 119: Where a street consists of buildings with varying height and character, a new development of up to one storey taller than its neighbours is usually possible.