Mansard Roof Extensions · SE20 Anerley
Bromley controls SE20's conservation areas around Penge; SE20 is one of south-east London's most affordable period markets.
The borough-level guide to mansard roof extensions in Bromley sets out how the same work is handled across the rest of the authority.
A mansard roof extension adds a full storey behind a new sloping front face — a strong option on SE20's terraces in Anerley where a standard dormer is too small. Bromley Council scrutinises mansards on townscape and precedent, especially within Alexandra Cottages, Penge High Street, Crystal Palace Park; we design to the borough's roof guidance with a Heritage Statement where the setting requires it.
Anerley's most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards that get approved in Anerley conservation areas — with heritage statements and planning officer negotiation built in.
Across Penge, Anerley, Crystal Palace Park fringe in SE20, the dominant property is victorian and edwardian terraces and villas around penge and anerley, with mansion blocks and post-war pockets near the crystal palace park. That stock shapes what mansard roof extensions looks like here: the right approach for a period terrace differs from a mansion-block flat or a new-build, and Bromley Council judges each on design quality and neighbour impact. We survey the specific Anerley property, confirm the planning route — Permitted Development, a Lawful Development Certificate, or full planning — and draw a council-ready set tailored to the SE20 streetscape.
Housing stock in SE20: Victorian and Edwardian terraces and villas around Penge and Anerley, with mansion blocks and post-war pockets near the Crystal Palace park.
Within the district: Penge, Anerley, Crystal Palace Park fringe.
Streets we know in SE20: the Alexandra Cottages, the Penge High Street area, Maple Road and the Anerley streets. Each road has its own building line, boundary treatment and precedent that Bromley Council weighs when assessing a mansard roof extensions scheme.
Conservation areas: Alexandra Cottages, Penge High Street, Crystal Palace Park. Inside these, most external work needs full planning and a Heritage Statement.
Getting around SE20: Penge West and Anerley on the Overground, plus Penge East and Kent House rail.
Property values: the cheapest large category in this borough by some distance is flats, at a £335,000 median in 2025, while Bromley's all-property median was £525,000. SE20's own median came in at £420,000.
Borough character: Largest London borough by area; substantial Green Belt; conservation areas in most town centres; generally permissive elsewhere.
We check against Bromley Council's mansard design guide and design to match the terrace.
Required for Anerley's conservation areas — demonstrates the mansard respects character and townscape.
Accurate photomontage showing how the mansard sits alongside neighbours — often decisive at Bromley Council committee.
Mansards invariably trigger Party Wall notices in Anerley's dense terraced streets. Structural package includes new ridge, tie beams, floor joists.
Full liaison with Bromley Council planning officer, committee representation if called in.
Part L thermal, Part B fire (critical on mansards), Part E acoustic separation.
Single planning or building-regs submission.
Planning + building regs + structural.
Listed, conservation or complex sites.
Yes. The Victorian and Edwardian terraces and villas around Maple Road and the Anerley streets suit side-return, rear and loft extensions, much of it within Permitted Development outside the conservation areas, confirmed with a Lawful Development Certificate. We confirm the route and draw to Bromley's checklist.
Alexandra Cottages is a conservation area of distinctive Victorian model-housing with strong uniform character, so external changes there are tightly assessed on materials and form. We design sympathetically and submit a full application with a Heritage Statement where the designation applies.
Usually yes outside the conservation areas — a rear dormer or L-shape within the volume allowance, confirmed by a Lawful Development Certificate. Inside the Alexandra Cottages or Penge High Street designations, roof changes need full planning. We confirm which applies to your road.
The Overground link keeps demand strong.
Bromley Council charges its own statutory application fee (currently £548 for a householder planning application, £610 for a full application). We quote the drawings as one fixed price and the free site survey covers every SE20 address.
For a SE20 project across Penge, Anerley, Crystal Palace Park fringe, expect roughly 3–4 weeks from instruction to submission: week 1 the measured survey, weeks 2–3 the drawings and your revisions, then validation and the statutory determination by Bromley Council (8 weeks for a householder application). We carry the Anerley application through every officer query to the decision.
Anerley (SE20) sits primarily in Bromley, so applications are decided by Bromley Council. Conservation areas within SE20 include Alexandra Cottages, Penge High Street, Crystal Palace Park, where full planning and a Heritage Statement are required. We confirm the planning route for your exact address before quoting.
Almost always. Any structural work behind mansard roof extensions in Anerley — new openings, steel beams, loft floors, foundations — needs Building Regulations approval covering structure (Part A), fire escape (Part B) and insulation (Part L), submitted to Bromley Council Building Control or an approved inspector. On SE20's typically terraced and semi-detached stock, a Party Wall notice to adjoining neighbours is normally required before the steelwork. We coordinate both as part of the Complete package.
In value terms, yes. The bigger risk is an unapproved or non-compliant scheme — which is why council-ready drawings and a clean Building Control sign-off matter on SE20 homes.
Working across a borough boundary, or unsure which council will decide your application? Every service we offer is listed for SE9, SE12, SE26, BR1, BR2, BR3, BR6 and BR7.
Pick a slot that suits you. No obligation and no sales pressure, just straight answers on your planning route.
Every SE20 postcode district we draw in, the stock that dominates it and the authority that validates a mansard roof extension there. SE20 fees below are the statutory England rates for 2026, not mansard roof extension estimates.
| Postcode | Area | Dominant stock | What it means for a mansard roof extension |
|---|---|---|---|
| SE20 | Anerley / Penge | Victorian and Edwardian terraces | Anerley / Penge is split at SE20. Either Bromley Council or Croydon Council can determine a mansard roof extension here, so the SE20 address is checked against both policies maps first. |
| SE20 | Penge | Victorian and Edwardian terraces | Penge sits inside SE20; mansard roof extension proposals here are determined by Bromley Council. |
| BR1 | Bromley / Bickley | Victorian terraces, Edwardian villas, post-war flats | Adjoining district to SE20, also inside Bromley for mansard roof extension purposes. |
| BR2 | Hayes / Keston | Victorian terraces, Edwardian villas, post-war flats | Adjoining district to SE20, also inside Bromley for mansard roof extension purposes. |
| BR3 | Beckenham | Edwardian villas, 1930s semi-detached | Adjoining district to SE20, also inside Bromley for mansard roof extension purposes. |
| SE19 | Upper Norwood / Crystal Palace | Victorian villas, Edwardian terraces | Adjoining district to SE20, also inside Croydon for mansard roof extension purposes. |
| SE25 | South Norwood / Selhurst | Victorian terraces | Adjoining district to SE20, also inside Croydon for mansard roof extension purposes. |
| CR0 | Croydon / Addiscombe / Shirley | Edwardian terraces, post-war flats | Adjoining district to SE20, also inside Croydon for mansard roof extension purposes. |
| CR2 | South Croydon | mixed stock | Adjoining district to SE20, also inside Croydon for mansard roof extension purposes. |
Roof pitch, wall build-up and plot depth change every few SE20 streets, and each one changes what a mansard roof extension can achieve at that address.
How designation changes a SE20 (Anerley / Penge) mansard roof extension: Bromley Council maintains 48 conservation areas, including Keston, Bickley, Bromley Town. Inside any of them a SE20 (Anerley / Penge) mansard roof extension cannot rely on permitted development, and the route becomes a £548 householder application determined in 8 weeks rather than a £249 prior approval in 6 weeks. Bickley sets the tone for SE20 (Anerley / Penge) casework.
No blanket Article 4 over SE20 (Anerley / Penge): Bromley Council has not withdrawn permitted development across SE20 (Anerley / Penge), so a mansard roof extension outside a SE20 (Anerley / Penge) conservation area usually keeps it. The £274 Lawful Development Certificate is still the document a SE20 owner wants on file.
SE20 (Anerley / Penge) housing stock: Large 1930s detached and semi-detached in Chislehurst and Bickley; Edwardian in Beckenham; Victorian in Bromley town; Metropolitan Green Belt covers significant rural-fringe land. Largest London borough by area; substantial Green Belt; conservation areas in most town centres; generally permissive elsewhere. Read that before choosing a mansard roof extension route in SE20 (Anerley / Penge) — construction, not postcode, sets what is achievable. Bromley Council charges £548 for a householder application and has 8 weeks to determine it.
How designation changes a SE20 (Anerley / Penge) mansard roof extension: Croydon Council maintains 24 conservation areas, including Purley, Shirley Park, South Norwood. Inside any of them a SE20 (Anerley / Penge) mansard roof extension cannot rely on permitted development, and the route becomes a £548 householder application determined in 8 weeks rather than a £249 prior approval in 6 weeks. Shirley Park sets the tone for SE20 (Anerley / Penge) casework.
No blanket Article 4 over SE20 (Anerley / Penge): Croydon Council has not withdrawn permitted development across SE20 (Anerley / Penge), so a mansard roof extension outside a SE20 (Anerley / Penge) conservation area usually keeps it. The £274 Lawful Development Certificate is still the document a SE20 owner wants on file.
SE20 (Anerley / Penge) housing stock: Victorian villas in Upper Norwood and Crystal Palace; Edwardian terraces in Thornton Heath and Selhurst; 1930s semi-detached in Purley and Coulsdon; post-war in Croydon central. Large, mixed-density outer borough; permissive in outer areas; heritage controls in conservation pockets; major regeneration in central Croydon. Read that before choosing a mansard roof extension route in SE20 (Anerley / Penge) — construction, not postcode, sets what is achievable. Croydon Council charges £548 for a householder application and has 8 weeks to determine it.
Sources for this SE20 mansard roof extension page: borough policies maps and conservation-area registers (2025–26), Royal Mail postcode district boundaries, the Town and Country Planning (Fees for Applications) (England) Regulations, the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended, and the Party Wall etc. Act 1996.
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