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Improving at SE9 4AJ

What you could build at SE9 4AJ: 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 Mottingham, Bromley.

71extensions seen within 600 m in the last 10 years

3loft conversions within 600 m in the last 10 years

79%of 57 householder applications nearby approved (since 2023)

95.9extensions 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.
Not in a conservation area (from council registers).
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.

What neighbours have built

Home	Work	Seen	Space added	Floor area	Rooms	Distance
128, Castlecombe Road	Extension	2026	+24 m²	66 m² → 90 m²	–	83 m
83, Framlingham Crescent	Extension	2026	+53 m²	71 m² → 124 m²	4 → 6	317 m
1, Offenham Road	Extension	2026	+27 m²	73 m² → 100 m²	–	436 m
10, Downs Avenue	Extension	2026	+96 m²	98 m² → 194 m²	4 → 7	448 m
78, Cranmore Road	Extension	2026	+15 m²	78 m² → 93 m²	–	503 m
8, Elmstead Avenue	Extension	2026	+21 m²	102 m² → 123 m²	5 → 6	584 m

Planning applications nearby

Address	Work	Outcome	Decided	Drawings and agent
32b, St Keverne Road, Se9 4aa	Windows, doors or cladding	Under consideration	–	25/01208/FULL6
15, Horley Road, Se9 4lf	Other householder work	Under consideration	–	25/01399/FULL6
66, Cranmore Road, Br7 6et	Rear extension	Under consideration	–	25/01538/FULL6
20, Cranmore Road, Br7 6es	Rear extension	Under consideration	–	25/01488/FULL6
63, Castlecombe Road, Se9 4au	Other householder work	Not needed / lawful	Jun 2025	25/01765/HHPA
3, Broadheath Drive, Br7 6eu	Rear extension	Refused	Jun 2025	25/01665/HHPA

How often householder applications are approved

Work	Mottingham	Bromley	London	Typical decision time
All householder applications	78% (60)	79% (3770)	80%	8 weeks
Loft or dormer	92% (13)	73% (1144)	81%	8 weeks
Rear extension	78% (18)	89% (1056)	79%	8 weeks
Two-storey extension	65% (17)	70% (543)	72%	8 weeks
Other householder work	60% (5)	54% (294)	70%	8 weeks
Side return or wrap-around	–	94% (154)	88%	8 weeks
Windows, doors or cladding	–	85% (85)	90%	8 weeks
Outbuilding or garden room	–	83% (107)	79%	8 weeks
Side extension	–	93% (144)	86%	8 weeks
Garage conversion or garage

Cost and the value it adds

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 (124,884 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 Mottingham.

Your home is worthExtra space you need (m²)Homes here sell for, per m²Building cost per m²Share of that an extension adds (%)

Move to a home 20 m² bigger (about £521,000)

Stamp duty on the new home	£16,050
Estate agent on yours 1.2% + VAT	£5,904
Solicitors, buying and selling	£3,000
Survey	£600
Removals	£1,500
Money gone	£27,054

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	−£66,600
Money gone	−£9,100

On these figures, extending loses about £36,154 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.

Find help: RIBA Find an Architect ↗ · CIAT architectural technologists ↗ · TrustMark tradespeople ↗ · Federation of Master Builders ↗ · Planning Portal guides ↗

General guidance, not planning or legal advice. Fees and rules as checked in October 2026; confirm with the council.

Energy certificates: MHCLG (OGL). Planning applications: GLA Planning London Datahub. Conservation areas and Article 4: planning.data.gov.uk (OGL).

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Improving at SE9 4AJ

The rules at this address

What neighbours have built

Planning applications nearby

How often householder applications are approved

Cost and the value it adds

Move or improve?

Getting started

Go deeper

Improving at SE9 4AJ

SE9 4AJ is on Framlingham Crescent

The rules at this address

What neighbours have built

Planning applications nearby

How often householder applications are approved

Cost and the value it adds

Move or improve?

Getting started

Go deeper

SE9 4AJ is on Framlingham Crescent