What you could build at SE21 7ED: the planning rules at this address, what neighbours have built and how big, planning decisions nearby, rough costs and the value an extension adds, and how to get started. In Herne Hill & Dulwich Park, Southwark.
119extensions seen within 600 m in the last 10 years
13loft conversions within 600 m in the last 10 years
134extensions per 1,000 homes in the neighbourhood (10 years)
● work seen on energy certificates · ● application approved · ● refused · ● pending or other · ● this postcode
The rules at this address
Houses usually have permitted development rights: some rear extensions (typically up to 3 m deep for a semi or terrace, 4 m detached), loft conversions within volume limits, and porches can go ahead without planning permission. Larger single-storey rear extensions (up to 6 m / 8 m) can use the “prior approval” neighbour scheme.
In the Dulwich Village conservation area: permitted development is narrower (for example no side extensions or roof cladding), and demolition and works to trees need consent.
No Article 4 direction recorded for this postcode.
Listed buildings need listed building consent for most changes, inside and out: check the National Heritage List.
To be certain work is permitted development, apply for a lawful development certificate (about £129 for householders in England). Building regulations apply either way.
Across England and Wales, homes extended by a typical 30 m² and then resold rose about 11.1% more than similar homes nearby over the same years (126,300 resales). How extensions pay off by size, type and region.
Single-storey rear or side extension: about £2,000–£3,000 per m² (London £2,500–£4,000), plus fees and VAT
Loft conversion: about £45,000–£75,000 for a dormer; more for a mansard or hip-to-gable
Two-storey extension: about £1,800–£2,800 per m² of new floor
Garage conversion: about £15,000–£30,000
Basement: about £3,500–£5,000 per m², London mostly
Build costs are rough 2026 ranges from industry guides, not quotes. Get three quotes for your plans.
Move or improve?
The money you don't get back either way, for the same extra space in Herne Hill & Dulwich Park.
Move to a home 20 m² bigger (about £1,544,000)
Stamp duty on the new home
£99,030
Estate agent on yours 1.2% + VAT
£19,584
Solicitors, buying and selling
£3,000
Survey
£600
Removals
£1,500
Money gone
£123,714
Extend by 20 m²
Building, plus 15% for design, planning and contingency
£57,500
Less what it adds to your home's value 60% of the local price
−£110,400
Money gone
−£52,900
On these figures, extending loses about £176,614 less. Moving also changes the area, the schools and the commute; extending means months of building work and depends on planning.
Building costs vary a lot (a single-storey rear extension is often £2,000–£3,000 per m², more in London). How much space adds depends on the home and street: what extensions added to resale prices. A guide, not advice; nothing you type leaves this page.
Getting started
Look at what neighbours did. Open applications above to see drawings that were approved on similar houses, and who designed them.
Check the route: permitted development (with a lawful development certificate), prior approval for larger rear extensions, or full householder planning permission.
Get a measured survey and a designer: an architect, an architectural technologist or a designer who handles planning drawings.
Apply (householder permission is about £258 in England; councils aim to decide within 8 weeks).
Building regulations through the council's building control or an approved inspector, and party wall notices to neighbours if you build on or near the boundary.
Choose a builder: written quotes, a contract, staged payments, and check their insurance and references.
From energy certificates: an extension where a later certificate shows more floor space, a loft conversion where roof rooms appear. Certificates come with sales, lettings and some building work, so the year is when it was first seen.
Not every extension shows here. We only see building work when a new energy certificate is lodged, which happens when a home is sold, let or newly built. A loft or extension added since then won't appear, even with planning permission and building control sign-off, because those records aren't published as open data outside London. Missing work doesn't mean missing paperwork.
Sept 2026
26/AP/2105
50, Norcroft Gardens, Se22 0bh
Two-storey extension
Approved
Aug 2026
26/AP/1843
384, Lordship Lane, Se22 8nd
Loft or dormer
Under consideration
–
26/AP/1870
386, Lordship Lane, Se22 8nd
Loft or dormer
Under consideration
–
26/AP/1869
252, Barry Road, Se22 0js
Loft or dormer
Approved
Aug 2026
26/AP/1768
252, Barry Road, Se22 0js
Loft or dormer
Approved
Jul 2026
26/AP/1618
422, Lordship Lane, Se22 8ne
Rear extension
Approved
Jul 2026
26/AP/1459
39, Landells Road, Se22 9pq
Side return or wrap-around
Approved
Jul 2026
26/AP/1455
422, Lordship Lane, Se22 8ne
Outbuilding or garden room
Approved
Jun 2026
26/AP/1457
422, Lordship Lane, Se22 8ne
Loft or dormer
Approved
Jul 2026
26/AP/1458
216a, Barry Road, Se22 0js
Loft or dormer
Approved
Jun 2026
26/AP/1066
17, Court Lane Gardens, Se21 7dz
Rear extension
Approved
May 2026
26/AP/0796
17, Court Lane Gardens, Se21 7dz
Loft or dormer
Approved
May 2026
26/AP/0797
97, Beauval Road, Se22 8uh
Other householder work
Refused
Apr 2026
26/AP/0644
7, Thompson Road, Se22 9jr
Loft or dormer
Approved
Apr 2026
26/AP/0457
218a, Barry Road, Se22 0js
Loft or dormer
Approved
Apr 2026
26/AP/0489
49, Underhill Road, Se22 0qz
Loft or dormer
Approved
Apr 2026
26/AP/0469
187, Friern Road, Se22 0bd
Loft or dormer
Approved
Apr 2026
26/AP/0443
15, Mount Adon Park, Se22 0ds
Garage conversion or garage
Approved
Feb 2026
26/AP/0050
129, Court Lane, Se21 7ee
Rear extension
Approved
Jan 2026
25/AP/3435
2, Belvoir Road, Se22 0qy
Two-storey extension
Under consideration
–
25/AP/3140
266, Friern Road, Se22 0bb
Loft or dormer
Approved
Feb 2026
25/AP/3432
131, Court Lane, Se21 7ee
Other householder work
Approved
Feb 2026
25/AP/3310
145, Court Lane, Se21 7ee
Loft or dormer
Approved
Mar 2026
25/AP/3369
45, Underhill Road, Se22 0qz
Loft or dormer
Approved
Jan 2026
25/AP/3281
17, Norcroft Gardens, Se22 0bh
Rear extension
Approved
Dec 2025
25/AP/3146
286, Upland Road, Se22 0dp
Loft or dormer
Approved
Dec 2025
25/AP/3027
131, Court Lane, Se21 7ee
Loft or dormer
Approved
Jan 2026
25/AP/3004
145, Court Lane, Se21 7ee
Outbuilding or garden room
Approved
Nov 2025
25/AP/2819
21, Landells Road, Se22 9pg
Side return or wrap-around
Approved
Oct 2025
25/AP/2544
218, Barry Road, Se22 0js
Loft or dormer
Approved
Oct 2025
25/AP/2465
219 Flat 1, Friern Road, Se22 0bd
Rear extension
Approved
Oct 2025
25/AP/2254
297, Upland Road, Se22 0dn
Loft or dormer
Approved
Jan 2026
25/AP/2191
4, Donkey Alley, Se22 0ny
Loft or dormer
Approved
Dec 2025
25/AP/2293
20, Dulwich Common, Se21 7ex
Rear extension
Approved
Sept 2025
25/AP/1900
Householder applications validated since 2023 within 600 m. The council's page has the drawings, the decision notice and who the agent or architect was. Hover a row for the description. Source: GLA Planning London Datahub.
Garage conversion or garage
–
100% (47)
88%
7 weeks
Basement
100% (10)
96% (47)
83%
8 weeks
Porch or front extension
–
100% (19)
81%
7 weeks
Share of decided applications approved since 2023 (number decided in brackets). Withdrawn applications aren't counted; many are withdrawn when refusal looks likely.