Client brief
A combined extension and loft conversion, bringing together a larger kitchen and living area with an improved garden connection and bathroom provision.
Lewisham Planning Guide
Extensions and Loft Conversions in Lewisham
Lewisham Council has particularly detailed design guidance for residential extensions and roof alterations.
Lewisham project · 2017
A combined extension and loft conversion
Planning constraints
The design had to be read against the Lewisham principles covered in this guide:
- keep a typical rear extension within the general 3m projection starting point where applicable;
- manage the height and mass of any side-return or infill extension at the boundary;
- retain the original roof form and use appropriate dormer setbacks; and
- protect neighbouring daylight, outlook and the remaining garden area.
Design solution
The combined project brought together a larger kitchen and living area, a stronger connection to the garden and improved bathroom provision. The loft conversion extended the home upwards while the general arrangement drawing records the proposed ground-, first- and roof-level organisation.
Project album
Kitchen, living, garden and bathroom spaces
Explore the full Lewisham project album from our past projects, including the finished kitchen, living room, garden connection, bathroom and the general arrangement drawing.
This advice is based on the planning policy and guidance in force in 2026 and is subject to change.
Its Alterations and Extensions SPD contains dedicated guidance for rear extensions, side extensions, infill extensions, two-storey extensions, dormers, hip-to-gable extensions, L-shaped roof extensions and mansards.
That means the design of an extension should take Lewisham’s local guidance into account from the outset rather than relying solely on national permitted development limits.
Rear Extensions in Lewisham
For typical terraced and semi-detached houses, Lewisham’s guidance states that extensions should generally not project more than 3 metres to the rear.
Greater depths can potentially be appropriate on detached houses or unusually large sites.
The extension should not occupy more than half the depth of the original rear garden.
Side Return Extensions in Lewisham
Side-return or infill extensions are common on Victorian houses throughout the borough.
Lewisham generally expects them to remain single storey.
For an extension up to approximately 3 metres deep, the guidance indicates a height of no more than around 3 metres.
Where an extension exceeds 3m in depth, proposals exceeding approximately 2.5 metres in height at the boundary are unlikely to be supported.
The boundary height can therefore be a critical part of the design of a deeper side-return extension.
Wrap-Around Extensions
A wrap-around extension combines the side-return infill with an extension behind the original rear return.
Lewisham expects these additions to remain subordinate to the original building.
Contemporary, lightweight designs can sometimes work particularly well because they allow the form of the historic rear return to remain visible.
Side Extensions
Lewisham normally expects a single-storey side extension to remain subordinate to the existing building.
The Council’s guidance recommends that it:
- is normally set at least 150mm behind the original front façade;
- is generally no wider than half the width of the original house; and
- has a roof form that complements the existing building.
Two-Storey Rear Extensions
Two-storey rear extensions are considerably more difficult to achieve.
Lewisham identifies potential problems including overlooking, overshadowing, loss of daylight and an increased sense of enclosure.
The Council states that two-storey rear extensions will only be considered where exceptional design quality can be demonstrated and the effect on neighbours is acceptable.
They are generally unacceptable within conservation areas.
Loft Conversions in Lewisham
Loft conversions can range from simple rooflights to substantial rear roof extensions.
Rooflights should remain subordinate to the roof and ideally sit flush within the roof slope.
Lewisham states that rooflights should not project more than 150mm above the original roof slope.
Rear Dormers
Lewisham provides particularly useful dimensional guidance for rear dormers.
They should generally be set:
- 300mm from each party wall;
- 300mm below the ridge;
- 300mm from a hip; and
- 300mm above the existing eaves.
The dormer should remain visually subordinate and its windows should relate appropriately to the openings below.
Rear Roof Extensions
Larger rear roof extensions should also retain visible portions of the original roof.
Within conservation areas, Lewisham applies a substantially more restrictive approach.
The Council states that rear roof extensions should be significantly inset from the ridge, eaves and sides and should be no wider than two-thirds of the original unextended roof.
Lewisham Conservation Areas
Conservation-area extensions are expected to use particularly high-quality materials and detailing.
Two-storey rear additions are normally resisted, while large side dormers and roof extensions can also be difficult.
For infill extensions, Lewisham generally favours a lightweight appearance that allows the original rear return to remain visually identifiable.
Planning an Extension in Lewisham?
Draw & Plan prepares planning drawings for extensions and loft conversions throughout Lewisham, including Brockley, Hither Green, Catford, Forest Hill, Sydenham and surrounding areas.
Planning a Lewisham Extension or Loft Conversion?
Send us your address and a short description of the work you are considering and we can advise on the drawings required.
Frequently Asked Questions
Frequently Asked Questions
How deep can a rear extension be in Lewisham?
For typical terraced and semi-detached houses the SPD indicates around 3m as the general design starting point, although the circumstances of the site remain important.
How high can a Lewisham side return be?
For an extension up to about 3m deep, around 3m high can be appropriate. Where the extension is deeper than 3m, a boundary height exceeding around 2.5m is unlikely to be supported.
How far should a rear dormer be from the ridge in Lewisham?
Lewisham’s guidance recommends a minimum setback of approximately 300mm.
Can I build a wrap-around extension in Lewisham?
Often yes, but its depth, height and effect on neighbouring properties need to be carefully considered.
Are loft extensions harder in Lewisham conservation areas?
Yes. Larger roof extensions are much more tightly controlled and the original roof form should remain clearly legible.