House Extensions London

Not always. Some house extensions can be built under permitted development rights, but many London extension projects still need planning permission or formal confirmation from the council.

The correct route depends on the property type, extension size, location, previous extensions, planning history, conservation area status and whether any planning conditions or Article 4 Directions apply.

If you are unsure, we can review the property and advise whether permitted development, a Lawful Development Certificate, prior approval or a householder planning application is likely to be the right route.

Possibly. Many houses have permitted development rights for certain rear extensions, side extensions and other alterations, but the works must stay within strict limits and conditions.

Permitted development can be restricted for flats, maisonettes, listed buildings, conservation areas, Article 4 areas, previously extended homes and properties with planning conditions attached.

Where permitted development is being relied upon, we usually recommend applying for a Lawful Development Certificate so you have written confirmation from the council before building.

For most house extensions, professional drawings and advice are strongly recommended, even where the project is relatively small. A good extension needs to work practically, respond to planning rules, consider neighbouring properties and provide clear information for planning, building regulations and builders.

At Detailed Planning, our team includes ARB-registered Architects and CIAT Chartered Architectural Technologists. We prepare architectural drawings, advise on the most suitable planning route and help move projects from early design through to planning and building regulation drawings.

Even a small rear extension can involve permitted development rules, drainage, structure, insulation, ventilation, boundary issues and neighbour impact. Professional input can help avoid planning issues, poor layouts, unclear builder quotes and building control problems.

A builder will still be needed for construction pricing and the build itself, and a structural engineer is usually required for structural calculations.

Planning permission is about whether the development is acceptable in planning terms. It considers issues such as size, appearance, neighbour impact, overlooking, local character and planning policy.

Building regulations are about how the extension is constructed. They consider matters such as structure, insulation, fire safety, ventilation, drainage, access and energy performance.

You may need building regulations approval even if your extension does not need planning permission.

The cost of house extension drawings depends on the size and complexity of the project, the planning route, the number of design options required and whether building regulation drawings are also needed.

At Detailed Planning, we usually work on a fixed-fee basis for our architectural services, rather than charging a percentage of the build cost. This gives you more certainty from the outset and helps you understand what is included at each stage before committing.

A simple rear extension will usually be more straightforward than a wrap-around extension, conservation area project, two-storey extension or whole-house remodel. Following your enquiry, we can review the brief and provide a clear, competitive fee proposal tailored to your project.

Our aim is to offer a good value, planning-led service with clear drawings, practical advice and support through the key stages. Our Extension Cost Calculator can also help you consider likely build costs at an early stage.

House extension build costs vary depending on the floor area, structural work, glazing, specification, kitchen or bathroom works, drainage, site access and the builder you choose.

London projects can vary significantly, so early figures should be treated as a guide rather than a fixed price. A contractor’s quote will still be needed before construction starts.

Our Extension Cost Calculator can help you understand likely cost ranges before you commit to detailed design.

Structural engineer fees depend on the size and complexity of the extension, the amount of steelwork, foundation design, wall removals and whether site visits or extra details are required.

A common fee for a typical rear ground floor extension only may be around £1200 to £1800.

Most house extensions need structural calculations, especially where walls are removed, new openings are formed, steel beams are required or new foundations are being built.

The engineer’s fee is usually separate from architectural fees. We can coordinate our building regulation drawings with the engineer’s information so the architectural and structural packages work together.

For planning, the council usually needs existing and proposed drawings such as floor plans, elevations, roof plans, site plans and block plans. The exact requirements depend on the application type and local authority.

For building regulations, the drawings are more technical and may include construction notes, build-ups, drainage principles, fire safety notes, ventilation information and key details.

We can prepare both planning drawings and building regulation drawings depending on the stage of your project.

The design stage varies depending on the complexity of the brief and how quickly decisions are made. Once a householder planning application is submitted, councils commonly work to an eight-week decision period, but validation delays, amendments, officer workload and committee referrals can extend this.

We recommend 6 weeks to agree designs, 8 weeks for planning applications and 6-12 weeks for the remaining documents and approvals such as building regulation drawings, party wall agreements, building control sign off etc. 

Permitted development and Lawful Development Certificate applications can also take time, so it is best to allow for the approval process before booking builders.

We can explain the likely timeline at the start based on your project route.

Often, yes. Side return extensions are common on London terraced houses, but they can be planning-sensitive because of neighbour impact, light, outlook and design quality.

Typically for deeper extensions, the boundary wall height should be limited to 2m (slightly above the existing fence) if there is an adjoining neighbour.

Some side return extensions may fall within permitted development, but many London side return and wrap-around extensions require planning permission. This is particularly common where the proposal extends close to boundaries, affects the rear elevation or is in a conservation area.

We can review the site and advise on the most suitable planning route before developing the drawings.

Wrap-around extensions are possible on many London homes, but they often need careful planning because they combine rear and side extension elements. These are never normally considered permitted development so planning permission is required. Observing the 45 degree rule from neighbours nearest window is advisable.

Councils usually consider the scale, depth, width, height, relationship to neighbouring properties, appearance and effect on the original house. In conservation areas, design and materials may be assessed more closely.

A planning-led design process can help test what is realistic before the application is submitted.

Yes, but the design usually needs to respond more carefully to the character and appearance of the conservation area.

The council may look closely at the scale, materials, roof form, glazing, visibility from public views and the effect on the original building. A standard set of drawings may not be enough for more sensitive sites, and a design, access or heritage statement may be required.

We regularly help homeowners prepare conservation area planning applications across London.

Possibly, but extensions to flats and maisonettes are usually more restricted than extensions to houses. Permitted development rights are generally more limited, and planning permission is often required for external alterations or extensions.

There may also be freeholder consent, lease restrictions, party wall matters and building control requirements to consider.

We can advise on the planning route and prepare the drawings needed for a council application where appropriate.

A well-designed house extension can be worth it if it creates useful space, improves the layout and helps the home work better for your lifestyle.

Extending can also avoid some of the costs and disruption of moving, such as stamp duty, estate agent fees, legal costs and the risk of compromising on location. It can also give you the opportunity to design the space around how you actually want to live.

The value depends on the property, location, build cost, design quality and local market. It is sensible to consider both the lifestyle benefit and the likely financial return before starting.

Moving may be the right option if your current home or location no longer works, but it can come with major costs, uncertainty and compromise. Stamp duty, legal fees, estate agent fees, removals and the cost of adapting a new home can all add up.

Extending can allow you to stay in an area you like while creating the space you need. It also gives you the chance to improve the layout, add value and design something more personal than a standard house move may offer.

The best route depends on your budget, property potential, local planning constraints and long-term plans.

Yes. Once planning permission is granted, we can help move the project into the technical stage by preparing building regulation drawings and coordinating with the structural engineer where required.

These drawings can then be used for building control and to help builders understand the proposed construction.

We can also remain available for reasonable questions during the build, although we do not act as the main contractor or replace the builder’s site responsibilities.

Where suitable, we can introduce trusted builders who have experience with residential extension projects. The builder’s appointment, quotation, programme and construction contract remain between you and the contractor.

Good drawings can help builders price the work more clearly, but it is still important to compare quotes, understand exclusions and check experience before choosing who to instruct.

For a single-storey rear extension, permitted development rules commonly allow a rear projection of up to 4 metres for a detached house or 3 metres for other houses, measured from the original rear wall of the house.

In some cases, the neighbour consultation / prior approval route may allow these depths to increase to 8 metres for detached houses or 6 metres for other houses, but this is not automatic and still needs the correct council process before works start.

Side extensions may also be possible under permitted development, but they are usually limited to single-storey extensions and must not be wider than half the width of the original house. For single-storey extensions, the maximum height is usually 4 metres, with eaves height limited to 3 metres where relevant boundary rules apply.

Two-storey rear extensions may be possible under permitted development in limited circumstances, but the rules are much stricter. They are usually limited to the rear of the original house, must not extend beyond the rear wall by more than 3 metres, and must meet additional boundary, roof pitch, window and design restrictions.

Permitted development rules are detailed, and previous extensions, conservation areas, Article 4 Directions, flats, maisonettes, listed buildings and planning conditions can all affect what is allowed. We normally recommend checking the route carefully and applying for a Lawful Development Certificate where permitted development is being relied upon. Government technical guidance confirms the standard rear extension limits and the larger home extension prior approval route, while Planning Portal guidance also sets out the more restrictive rules for two-storey extensions.

It’s likely, unless your neighbours aren’t close. You may need to follow the party wall process if your extension involves work close to a neighbouring property. This commonly applies when you are excavating within 3 metres of a neighbour’s structure, building on or near the boundary, building astride the boundary line, inserting beams into a shared wall, removing a chimney breast from a party wall, or carrying out structural works that affect a shared wall.

The process usually starts by serving the correct party wall notice on the affected neighbour. If they consent, the works can normally proceed. If they dissent or do not respond, party wall surveyors may need to be appointed and a party wall award prepared before the relevant works start.

You can read the Government guidance here: Party walls and building work: GOV.UK guidance.

Party wall matters are separate from planning permission and building regulations, so even if your extension is approved by the council, you may still need to deal with party wall requirements before starting work.