Policy information sourced from Lambeth Local Plan 2020-2035

Q11 Building alterations and extensions

  • A. The council is supportive in principle of building alterations and extensions where they have potential to deliver enlarged and additional residential units to meet Lambeth’s housing need. When considering proposals for the alteration or extensions of buildings the council will generally expect proposals:
    • i) to have a design which positively responds to the original architecture, roof form, detailing, fenestration (including design, materials and means of opening) of the host building and other locally distinct forms (such as group characteristics); such features should be respected, retained and where necessary on heritage assets authentically reproduced;
    • ii) to ensure, wherever possible, that new or replacement plant or equipment (for example: meter boxes, pipes, cables, antenna, air conditioning units) are fully integrated into the building, are not placed on publically-visible elevations and, where integration is not an option, are adequately and robustly screened;
    • iii) to, wherever possible, include energy efficiency improvements such as more efficient plant, improvements to thermal performance and renewable energy generation; and climate change adaptation measures such as improved shading on southern elevations and natural ventilation.

Extensions

  • B. Subordination will be a key consideration when assessing proposals for extensions. Development which unacceptably dominates the host building will not be permitted. Subordination, in all its forms, is particularly important in relation to heritage assets. To protect outdoor amenity space, as a general rule, no extension should reduce amenity space to less than the minimum required for that dwelling type by Policy H5.
  • C. Closet extensions are characteristic of many early- to mid-19th century buildings and should generally be retained. Where considered appropriate new closet extensions should generally reflect the following locally distinct patterns, especially on heritage assets:
    • i) come off a stairwell;
    • ii) have floor levels aligned with the stairwell half-landings;
    • iii) be a similar width to the stairwell;
    • iv) not obstruct the outlook from adjoining windows; and
    • terminate at least half a storey below eaves level.
  • D. Rear returns (also known as outriggers) are characteristic of many mid- late 19th century buildings in Lambeth and should generally be retained. New rear returns will normally be acceptable where they are characteristic of the building type and immediate locality.
  • E. Infill extensions (infilling the space along-side existing closet extensions or rear returns) should generally:
    • i) be single storey on heritage assets;
    • ii) have a glazed, light-weight appearance to differentiate them from the rear return; and
    • iii) be set back from the end of the main return on heritage buildings and not project beyond the end wall of the return above ground floor level elsewhere.
  • F. Full-width rear extensions will normally be supported where they meet criteria (a) (i) and (b).
  • G. Front extensions are not considered appropriate where they would unacceptably break the established building line or be at odds with the prevailing architectural character of the host building or its group.
  • H. Side extensions should:
    • i) retain sufficient side space above ground floor level to maintain gaps between buildings and prevent visual terracing. In suburban locations a minimum of 1m side space should generally be retained between the extended building and the property boundary. In some instances, for example on corner sites or in development affecting heritage assets, the retention of established spatial standards may deem all side extensions unacceptable.
    • ii) not unacceptably imbalance semi-detached pairs; and
    • iii) generally be set back from the corners of the building and with lower roofs than the main roof.
  • I. New dormers should:
    • i) be avoided on front roof pitches (unless similar buildings in the immediate context already exhibit appropriate front dormers);
    • ii) be subordinate (below the ridge and set in from the eaves and flanks) so that the roof remains the dominant element in the composition;
    • iii) be of design, materials and detailing appropriate to the host building; and
    • iv) have windows (solid, windowless dormers are generally not acceptable).
    • v) On sensitive buildings (including heritage assets), where dormers are considered appropriate in principle, they should also be modest in size, aligned with the openings below. Box dormers are considered unacceptable in sensitive heritage contexts.
  • J. Where rooflights fall under planning control they should generally be modest in size and be placed and aligned sensitively to respect the character of the host building. On heritage assets they will normally be resisted on street facing roof pitches; where considered appropriate they should be small in size and aligned with the windows on the elevation below.
  • K. Roof additions and mansards will not be permitted where they would harm the architectural integrity (building form and design integrity) of the original building or its group. Where considered appropriate on locally distinct buildings, mansards should:
    • i) replicate locally distinct forms, materials and detailing;
    • ii) preserve, extend or reinstate original features such as chimneystacks and pots, parapets and party wall upstands.
  • L. Other types of additional accommodation on roofs will normally only be acceptable on non-standard roof types where they comply with (a) (i) and (b).
  • M. Roof terraces and balconies will be assessed against Local Plan policy Q2 (Amenity). Where their loss is proposed as part of a roof extension, the re-provision of that amenity space will be required to meet the minimum requirements of Local Plan policy H5.
  • N. Living (green) roofs will be strongly encouraged for flat roofs which are not used as amenity space.

For more information please see the Local Plan