Mansard Roof Extensions · SW20 Raynes Park
Merton applies suburban householder control across SW20, with a conservation pocket around Cottenham Park; a settled family market.
This page covers one part of the borough. For the full picture — fees, timelines and the council's current position — read mansard roof extensions in Merton.
A mansard roof extension adds a full storey behind a new sloping front face — a strong option on SW20's terraces in Raynes Park where a standard dormer is too small. Merton Council scrutinises mansards on townscape and precedent, especially within Cottenham Park, Wimbledon West Side fringe; we design to the borough's roof guidance with a Heritage Statement where the setting requires it.
Raynes Park's most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards that get approved in Raynes Park conservation areas — with heritage statements and planning officer negotiation built in.
Across Raynes Park, West Wimbledon, Cottenham Park, Motspur Park fringe in SW20, the dominant property is inter-war and edwardian semis and detached houses around raynes park and west wimbledon, with larger houses toward wimbledon common. 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 Merton Council judges each on design quality and neighbour impact. We survey the specific Raynes Park property, confirm the planning route — Permitted Development, a Lawful Development Certificate, or full planning — and draw a council-ready set tailored to the SW20 streetscape.
Housing stock in SW20: Inter-war and Edwardian semis and detached houses around Raynes Park and West Wimbledon, with larger houses toward Wimbledon Common.
Within the district: Raynes Park, West Wimbledon, Cottenham Park, Motspur Park fringe.
Streets we know in SW20: the Cottenham Park roads, Coombe Lane, Grand Drive and the West Barnes streets. Each road has its own building line, boundary treatment and precedent that Merton Council weighs when assessing a mansard roof extensions scheme.
Conservation areas: Cottenham Park, Wimbledon West Side fringe. Inside these, most external work needs full planning and a Heritage Statement.
Getting around SW20: Raynes Park and Motspur Park rail to Waterloo, plus Wimbledon nearby for the District line and tram.
Property values: around £400,000 for a flat and £800,000-£1.3m for a house — a useful gauge of the build value an extension or loft adds in SW20.
Borough character: Wimbledon is heavily conservation-controlled; outer Merton (Morden, Mitcham) is permissive.
We check against Merton Council's mansard design guide and design to match the terrace.
Required for Raynes Park's conservation areas — demonstrates the mansard respects character and townscape.
Accurate photomontage showing how the mansard sits alongside neighbours — often decisive at Merton Council committee.
Mansards invariably trigger Party Wall notices in Raynes Park's dense terraced streets. Structural package includes new ridge, tie beams, floor joists.
Full liaison with Merton 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 inter-war and Edwardian semis and detached houses around Cottenham Park and Grand Drive suit rear, side and double-storey extensions plus loft conversions, much of it within Permitted Development outside the conservation area, confirmed with a Lawful Development Certificate. We confirm the route and draw to Merton's checklist.
Often, on the wider semi and detached plots around Coombe Lane — a two-storey side or rear extension, subject to Merton's design and neighbour-amenity policy on side-space and daylight. We design within those limits and produce the planning and Building Regulations drawings together.
Usually yes on the semis — a hip-to-gable plus rear dormer within the volume allowance, confirmed by a Lawful Development Certificate, provided you're not in the Cottenham Park conservation area. We check the constraints for your road and draw it for Building Control.
With SW20 houses around £800,000-£1.3m and direct rail links to Waterloo, a rear extension or loft adds family space worth comfortably above the build and drawing cost. SW20 is a sought-after family suburb.
With Raynes Park property at around £400,000 for a flat and £800,000-£1.3m for a house, the professional drawing fee is a small fraction of the value the work adds to SW20's inter-war and edwardian semis and detached houses. Merton Council charges its own statutory application fee on top (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 SW20 address.
For a SW20 project across Raynes Park, West Wimbledon, Cottenham Park, Motspur 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 Merton Council (8 weeks for a householder application). We carry the Raynes Park application through every officer query to the decision.
Raynes Park (SW20) sits primarily in Merton, so applications are decided by Merton Council. Conservation areas within SW20 include Cottenham Park, Wimbledon West Side fringe, 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 Raynes Park — 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 Merton Council Building Control or an approved inspector. On SW20'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. With Raynes Park (SW20) property at around £400, 000 for a flat and £800, 000-£1.3m for a house, a well-designed extension or loft typically returns more than it costs in added floor area and sale value. 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 SW20 homes.
If your site sits close to the edge of the borough, it is worth checking the authority next door. Browse everything we do in SW16, SW17 and SW19.
Pick a slot that suits you. No obligation and no sales pressure, just straight answers on your planning route.
Every SW20 postcode district we draw in, the stock that dominates it and the authority that validates a mansard roof extension there. SW20 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 |
|---|---|---|---|
| SW20 | Raynes Park | Victorian villas, Edwardian terraces | Raynes Park sits wholly inside SW20, so Merton Council validates every mansard roof extension submitted from an SW20 address. |
| SW20 | Wimbledon | Victorian villas, Edwardian terraces | Wimbledon sits inside SW20; mansard roof extension proposals here are determined by Merton Council. |
| SW19 | Wimbledon / Colliers Wood | Victorian villas, Edwardian terraces | Adjoining district to SW20, also inside Merton for mansard roof extension purposes. |
| SM4 | Morden | 1930s semi-detached, post-war flats | Adjoining district to SW20, also inside Merton for mansard roof extension purposes. |
| CR4 | Mitcham | 1930s semi-detached, post-war estates | Adjoining district to SW20, also inside Merton for mansard roof extension purposes. |
Roof pitch, wall build-up and plot depth change every few SW20 streets, and each one changes what a mansard roof extension can achieve at that address.
Conservation areas covering SW20 (Raynes Park): Merton Council runs 28, and Wimbledon Village, John Innes, Mitcham Cricket Green are the ones SW20 (Raynes Park) owners meet most. A mansard roof extension inside a SW20 (Raynes Park) conservation area loses permitted development, so the SW20 (Raynes Park) submission is a householder application at £548 decided in 8 weeks — not a £249 prior approval decided in 6 weeks. In Mitcham Cricket Green a mansard roof extension is judged on the street elevation first.
No blanket Article 4 over SW20 (Raynes Park): Merton Council has not withdrawn permitted development across SW20 (Raynes Park), so a mansard roof extension outside a SW20 (Raynes Park) conservation area usually keeps it. The £274 Lawful Development Certificate is still the document a SW20 owner wants on file.
SW20 (Raynes Park) housing stock: Victorian villas in Wimbledon; Edwardian terraces in Tooting and Colliers Wood; 1930s semi-detached in Morden and Raynes Park; post-war flats in Mitcham. Wimbledon is heavily conservation-controlled; outer Merton (Morden, Mitcham) is permissive. Read that before choosing a mansard roof extension route in SW20 (Raynes Park) — construction, not postcode, sets what is achievable. Merton Council charges £548 for a householder application and has 8 weeks to determine it.
Sources for this SW20 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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