Double Storey Extensions in SW London: Planning Rules

Quick answer: a double storey (two-storey) extension adds a room at first floor as well as ground floor, usually a bedroom or bathroom above a bigger kitchen. In South West London most need a householder planning application (£548 in England from 1 April 2026). In any conservation area, rear extensions of more than one storey are not permitted development at all, and large parts of Wandsworth, Merton, Richmond, Lambeth and Hammersmith & Fulham are conservation areas. Expect closer scrutiny of neighbours' light and outlook than for a single-storey job, party wall notices, and around eight weeks for a decision. We price double storey extensions individually after a site visit.

A single-storey kitchen extension is the most common job on a South West London terrace. A double storey extension is less common, but on the right house it solves two problems at once: a cramped kitchen downstairs and one bedroom too few upstairs. It also means building at first-floor level, close to neighbours' windows, which is why councils look at these schemes more carefully.

This guide explains how the planning route works, what each of our local councils tends to look for, and how the build differs from a ground-floor extension.

Which houses suit a double storey extension?

Start with the house and the plot, not the floor plan you want.

• Victorian and Edwardian terraces in Battersea, Earlsfield, Clapham and Fulham usually have a two-storey back addition already. Building above a side return, or extending the back addition upwards, is possible on some plots but runs straight into the neighbours' light and outlook.
• Inter-war and post-war semis towards Raynes Park, Wimbledon Park and East Sheen often have more side space and wider gardens, so there is more room for a first-floor addition that stays clear of next door.
• Detached houses give the most freedom, but on bigger plots in Wimbledon, Kew or Barnes they are also more likely to be in a conservation area or locally listed.

If the main thing you need is a bedroom, compare the double storey option with a loft. A rear dormer with an en-suite on a mid-terrace can often go ahead as permitted development outside a conservation area. Our loft conversion types guide compares the options.

The planning position

Conservation areas: always an application

The government's householder PD technical guidance is clear that on "Article 2(3) land", which includes conservation areas, rear extensions of more than one storey are not permitted development. Side extensions aren't either. So if your house is in any conservation area, a double storey extension needs a householder application.

That covers a lot of South West London:

• Wandsworth: 46 conservation areas, eight with Article 4 Directions.
• Lambeth: 62 conservation areas, including most of the streets around Clapham Common and Clapham Old Town.
• Richmond upon Thames: 85 conservation areas, plus Article 4 Directions street by street.
• Hammersmith & Fulham: 44 conservation areas, with Article 4 Directions on specific properties.
• Merton: many conservation areas in Wimbledon, including Wimbledon North, Wimbledon Village and Merton Hall Road, and Article 4 Directions in John Innes Merton Park and Wilton Crescent.

Outside a conservation area

Outside conservation areas, the national PD rules do allow some extensions of more than one storey at the rear, but with separate, tighter depth and boundary-distance limits than single-storey work. Side additions are more restricted again. Most double storey schemes on terraces and semis in our area end up outside those limits once the design reaches a useful size. If yours looks like it fits, get a Lawful Development Certificate (£274 from April 2026) before building, so you have written proof for a buyer's solicitor.

The larger home extension prior approval route (up to 6 m on a terrace) is only for single-storey extensions, so it doesn't help with a first-floor addition.

What councils look at

Each council has its own guidance, but the same themes come up.

• Wandsworth's Housing SPD covers rear and side extensions to terraced houses, including the effect on neighbours' light.
• Lambeth's Design Guide SPD (2023) includes its guidance on building alterations and extensions.
• Richmond's House Extensions and External Alterations SPD (2015) is the guide its planning officers use, whether or not your scheme needs permission. It treats 3 m (terraced), 3.5 m (semi-detached) and 4 m (detached) as usually acceptable depths for single-storey extensions, which gives you a sense of how carefully deeper, taller additions will be read. Richmond adopted a new Local Plan in October 2025.
• Merton's John Innes design guide says extensions there should be "subordinate to the main house; generally single storey with a pitched roof" and shouldn't rise above eaves level. In those two Article 4 areas, a double storey rear extension is a hard case.
• Hammersmith & Fulham applies Article 4 Directions to individual properties, so check the council's list first.

Before paying for full drawings, look up recent decisions on your street through the council's planning search. Approved schemes next door tell you a lot about what officers accept. Richmond also offers a pre-application advice service.

CIL: a Merton point for bigger schemes

Merton says any permission for at least 100 m² of new gross internal area will usually be liable for the Community Infrastructure Levy under both the Merton and Mayor of London charging schedules. A double storey extension alone may not get there, but one combined with a loft or a wraparound can. The householder exemption has to be claimed before work starts. Our Wimbledon and Merton planning guide explains how.

Party walls and neighbours

A double storey extension usually means deeper foundations than a single-storey job, and work close to or on the boundary. The Party Wall etc. Act 1996 applies if you dig within 3 m of a neighbour's building and deeper than its foundations, or within 6 m where the dig would cut a 45° line from the bottom of their foundations. Your neighbour has 14 days to reply in writing, and silence means a dispute is deemed to have arisen. See our party wall timeline for SW London.

It pays to talk to the neighbours before the application goes in. A first-floor wall close to their back windows is the thing most likely to prompt an objection.

How the build differs from a single-storey extension

• Structure. Upper floor joists, more steel and often bigger foundations. The structural engineer's design comes first, and building control inspects at the foundation stage.
• Joining the first floor. The new room has to meet the existing landing at a sensible level, which can mean moving a wall or reworking the stair landing.
• Roof. A pitched roof that matches the house is more common at first floor, and it is often what councils prefer.
• Building regulations. A new bedroom needs to meet the rules on structure, insulation and fire safety. A full plans application should be decided within five weeks, or two months if you agree.
• Living at home. The ground floor can usually be sealed off for a time, but the first-floor work disrupts bedrooms. Some families move out for part of the build.

On our Wimbledon whole-house renovation, the rear kitchen and dining extension was built alongside a loft conversion with a shower room over a 25-week programme. Combined schemes like that need the structure, stairs and services planned together from the start.

Cost: why we price at the site visit

A double storey extension doesn't fit a neat price band. Foundations, first-floor structure, roof form and finishes vary too much. We price it individually after a site visit, and the itemised quote excludes VAT and professional fees (design, structural engineer, Building Control, party wall and planning fees), which are quoted separately. Our fixed-price quote is based on the agreed written scope; client-requested changes and unforeseen work are priced and approved separately before proceeding.

For comparison, a typical kitchen or side return extension with us costs about £90,000–£100,000 to build (excluding VAT and professional fees; kitchen units, flooring and other second-fix items supplied by you), and a typical rear dormer loft with an en-suite about £80,000–£90,000.

Frequently asked questions

Do I need planning permission for a double storey extension?

In most South West London cases, yes. In conservation areas, rear extensions of more than one storey are never permitted development. Outside them, PD has tighter limits for two-storey work than for single-storey extensions, and most useful designs go beyond them.

Is a double storey extension or a loft better for an extra bedroom?

It depends on the house. On a mid-terrace outside a conservation area, a rear dormer loft can often go ahead as permitted development. A double storey extension can add a bigger kitchen as well, but it needs planning in most cases and has more effect on neighbours.

How long does planning take for a double storey extension?

Most householder applications are decided within about eight weeks. Allow time before that for a measured survey and drawings, and run party wall notices alongside.

Can I build a double storey extension in a Wandsworth conservation area?

You'll need a householder application, and the design has to suit the conservation area. Check the appraisal for your area and recent decisions on your street.

Does Merton allow two-storey extensions in John Innes Merton Park?

The council's design guide expects extensions there to be subordinate to the main house and generally single storey with a pitched roof, so a two-storey rear extension is difficult to justify.

Talk to us about extending up and out

Bluebird Spaces is based in SW19 and is a member of the Federation of Master Builders. We build house extensions in Wandsworth, Wimbledon, Putney, Battersea, Clapham, Fulham, Tooting, East Sheen and Richmond. Call 07564 041115 to book a free site visit, and we'll tell you honestly whether a double storey extension, a loft or a wraparound suits your house best.

Planning rules are property-specific. Always confirm the position with your council before you build.