Richmond House Extensions: Ideas, Planning and Cost Drivers

Richmond upon Thames has a huge variety of houses: Victorian terraces off Kew Road and Sheen Road, Edwardian semis in East Sheen, family houses in Kew and Barnes, and some very grand homes on Richmond Hill. That variety is why the "right" extension here depends so much on the house you start with.

This guide looks at the extension types that suit Richmond homes, the planning rules that shape them, what drives the cost (without pretending one number fits every house), and how the process runs from first visit to handover.

Start with the house, not the brochure

Victorian and Edwardian terraces

Most terraces in TW9, TW10 and St Margarets have a two-storey back addition with a narrow side passage beside it. That passage is the opportunity.

• Side return infill. Extending into the passage turns a narrow galley kitchen into a wide kitchen-diner. It's the most common Richmond terrace project.
• Wraparound. A side infill combined with a rear extension across the full width. It adds the most space, but also involves the most structure and the most neighbour contact.
• Rear extension only. Useful when the side passage is needed for access, bins or bikes, or when the back addition already holds the kitchen.

Edwardian and inter-war semis

In East Sheen, North Sheen and parts of Kew, semi-detached houses usually have wider plots and a side path. A full-width single-storey rear extension or an L-shaped extension that wraps part of the side is typical. The side path often has to stay for access to the rear garden.

Detached and larger family houses

Larger houses on Richmond Hill, in Kew and in Barnes give more room for depth. They're also more likely to be in a conservation area, listed, or recognised by the council as a Building of Townscape Merit. That doesn't rule out a contemporary extension, but materials, roof form and the amount of glazing get closer attention.

The planning rules that shape a Richmond extension

Permitted development, prior approval or a planning application

Under the national rules in the government's householder permitted development technical guidance, an attached house can usually add a single-storey rear extension of up to 3 m (4 m for a detached house) without planning permission, as long as it's no more than 4 m high. Outside conservation areas, the larger home extension route allows up to 6 m (8 m detached) through prior approval. The council notifies neighbours and has 42 days to decide.

Side extensions are tighter. They must be single storey, no more than 4 m high and no wider than half the original house. Where an extension fills the space between a side wall and a rear wall, as a side return does, the guidance says the side and rear limits both apply.

Conservation areas and Article 4

Richmond Council says the borough has 85 conservation areas. In a conservation area, the technical guidance removes permitted development for side extensions, for rear extensions of more than one storey, and for the 6 m prior approval route. A side return in a conservation area therefore always needs a householder application.

Richmond also uses Article 4 Directions street by street, and the council says "any home in the borough can be subject to an Article 4 Direction". Where a direction covers extensions, even a small rear extension needs permission. Our Richmond Article 4 guide explains how to check your address.

Richmond's own design guidance

Richmond's House Extensions and External Alterations SPD (2015) is the guide planning officers use, and it applies whether or not your scheme needs permission. Three points matter most for extensions:

1. Depth. It says a single-storey rear extension is usually acceptable if it projects no more than 3 m for a terraced house, 3.5 m for a semi-detached house and 4 m for a detached house. Site circumstances can justify more.
2. Side infills. For infills on Victorian houses that run deeper than those figures, it suggests limiting the eaves height to about 2.2 m to avoid a sense of enclosure for the neighbour.
3. Daylight. Extensions should pass the BRE 25-degree and 45-degree daylight tests, measured from the neighbour's windows.

The council adopted a new Local Plan in October 2025, so treat older approvals on your street as a guide rather than a guarantee.

Extension ideas that tend to work in Richmond

• A low, glazed side infill. Glazing along the boundary keeps the eaves low, brings light into the middle of the house and keeps the original back addition readable, which is what the SPD is after.
• A rear extension with a roof lantern or long rooflight. Where depth is limited to 3 m or 3.5 m, light from above makes a modest footprint feel much larger.
• Pitched or carefully detailed flat roofs in conservation areas. In sensitive streets, a roof that responds to the original house usually gets a better reception than a large, bulky flat box.
• Utility and storage in the plan. In many terraces the best gain isn't more floor area. It's moving the washing machine, boots and bikes out of the kitchen.
• Planning the loft at the same time. If a loft is likely later, designing both together avoids rebuilding the stair or re-routing services twice.

What drives the cost of a Richmond extension

We don't publish a single "price per square metre", because the same footprint can cost very different amounts on two houses. These are the items that move the number most. Our guide to what an extension quote should include goes into more detail.

1. Structure and openings. Removing the back-addition wall or the rear wall usually means steel beams and padstones, designed by a structural engineer.
2. Foundations and ground. Clay soils, nearby trees and old drains can all change foundation depth and design. Building over or near a public sewer may need the water company's approval.
3. Glazing. Large sliding doors, roof lanterns and frameless glass are often among the biggest single items.
4. Party walls. Surveyors' fees and any changes agreed in the award come into the budget.
5. The existing house. Rewiring, heating changes, new floors and decoration in the rooms you open up are often what make a project "whole-house".
6. Fees and approvals. Design, structural engineering, planning or certificate fees (a householder application is £548 in England from April 2026, under the government's fee schedule), building regulations approval and party wall costs all sit outside the build price.

Most single-storey extensions are well under 100 m², so the Community Infrastructure Levy won't normally apply. If yours is larger, check before you start.

How the process runs

1. Site visit and measured survey. Confirm the house type, constraints and what you need from the space.
2. Design and planning route. Decide between permitted development (ideally with a Lawful Development Certificate), prior approval and a householder application. A planning decision has an eight-week target.
3. Structural design and building regulations. Under a full plans application, the building control body should decide within five weeks, or two months if you agree to an extension, according to GOV.UK.
4. Party wall notices. Usually two months' notice for work to a shared wall, served once the structural design is clear. GOV.UK's party wall guidance explains your neighbours' options.
5. Build and handover. A written programme, regular site meetings and a building control completion certificate at the end.

You can see a finished example in our Sheen rear extension, an open-plan kitchen and dining space with full-height glazing.

FAQ

Do I need planning permission for a house extension in Richmond?

Not always. Outside conservation areas and Article 4 streets, many single-storey rear extensions are permitted development, and larger ones up to 6 m can go through prior approval. In a conservation area, side extensions and rear extensions of more than one storey need a householder application.

How deep can a single-storey extension be in Richmond?

Richmond's 2015 SPD treats 3 m (terraced), 3.5 m (semi-detached) and 4 m (detached) as usually acceptable, with more possible depending on the site. Permitted development and prior approval limits are separate national rules.

Can I build a side return extension in a Richmond conservation area?

Yes, with a householder planning application. Side extensions aren't permitted development in conservation areas, so the design needs to satisfy the SPD and the conservation area statement.

Will my neighbours be consulted?

Yes, for a householder application or a prior approval. Separately, if the work affects a shared wall, the Party Wall Act requires you to give your neighbours notice.

How long does a Richmond extension take from start to finish?

Allow for design, around eight weeks for a planning or certificate decision, and party wall notice running alongside. The on-site time depends on size and structure and is set out in a written programme once the design is fixed.

Talk to us about your Richmond extension

If you'd like a builder's view on what's realistic for your house, see our house extensions in Richmond page, then call 07564 041115 or email admin@bluebirdspaces.co.uk.

General guidance, not planning advice. Rules are property-specific, so always confirm with Richmond Council. Sources checked 4 October 2026.