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Many house extensions in London can be built under permitted development rights, depending on the size and type of extension, the planning history of the property and whether any restrictions apply. Properties in conservation areas, flats and previously extended homes may require full planning permission.

We assess the planning position early in the process and advise on the most suitable and lowest-risk route forward. In some cases, extensions that wrap around the house, connect to existing additions or involve unusual layouts can make a lawful development certificate less straightforward.

Planning permission is not something to be afraid of. Where there are doubts over permitted development, a householder planning application can sometimes be the safer route, as it allows more room for professional planning argument than a strict lawful development certificate assessment.

The construction cost of a house extension in London can vary significantly depending on the size, specification, structural complexity, level of glazing and site conditions. As a broad guide, many extensions fall between £2,500–£4,000+ per sqm excluding VAT, kitchens and professional fees.

For a relatively standard single-storey rear extension to a typical London mid-terrace property, a realistic build budget is often around £80,000–£120,000+, depending on the finish and level of structural alteration involved. You can also read our Extension Cost Calculator for further guidance.

Permitted development can allow certain extensions to be built without full planning permission, subject to size, height and design limitations. As a general guide, many semi-detached and terraced houses can extend up to 3m to the rear, while detached houses can often extend up to 4m.

Rear extensions are typically limited to a maximum eaves height of 3m and an overall height of 4m. Side extensions are usually restricted to no more than half the width of the original house and materials should generally match the existing property. The rules can become more complicated where previous extensions exist, so we advise on whether permitted development or a full planning application is the better route.

Loft conversion costs vary depending on the type of conversion, structural work and specification level. A standard rear dormer loft conversion in London often starts from around £75,000–£120,000+ excluding VAT and finishes. Larger mansard conversions or more complex roof alterations can cost significantly more.

We help clients maximise usable space, improve layout efficiency and understand likely build costs before progressing too far into the design stage. You may also find our Loft Conversion Checklist and guide on whether a loft conversion is worth it useful.

Planning permission relates to how a development looks, how it affects neighbours and whether it complies with local planning policy. Building regulations focus on the technical construction standards of the project, including structure, insulation, fire safety, drainage and energy performance.

Many projects require building regulations approval even where planning permission is not needed. Building regulation drawings contain the detailed technical information required for construction and help the builder comply with current regulations on site. Our guide, From Approval to Build-Ready, explains what typically happens after planning approval.

In many cases, internal wall removals do not require planning permission, particularly within standard houses. However, structural alterations will usually require building regulations approval and input from a structural engineer to ensure the work is carried out safely.

If the property is listed or located within certain protected buildings, additional permissions may also be required. We regularly help homeowners with property refurbishments and internal alterations to create brighter, more open-plan living spaces with improved flow, light and usability.

Converting a house into flats can be possible in some London boroughs, but it depends heavily on local planning policy, property size, location and housing restrictions. Some councils strongly resist the loss of family housing, while others may support well-designed conversions in suitable locations.

Policies vary significantly between boroughs. Some councils have conversion restriction areas, minimum size requirements for the original property, limits on the percentage of flats within a street, or policies discouraging conversions in predominantly family housing areas. Parking, public transport access, bin storage, cycle provision, garden space and Nationally Described Space Standards are also important.

We provide early feasibility studies and planning advice for flat conversion projects in London.

Some commercial buildings may be suitable for residential conversion, either through prior approval change of use routes or full planning permission, depending on the existing use class, location and property constraints.

Factors such as unit quality, natural light, ceiling heights, transport impact, external amenity space and local planning policy are all important considerations. We help assess conversion viability, review planning risks and advise on the most realistic strategy before significant investment is made.

A pre-application submission is an early-stage planning enquiry submitted to the local authority before a formal planning application. It allows the council to provide feedback on the principle of development, design concerns and potential planning risks.

Pre-application advice can help identify issues early and often improves the chances of a smoother planning application, particularly for larger extensions, flat conversions and new-build homes. In our experience, councils are often more approachable, flexible and willing to negotiate during the pre-application stage than during the formal planning process.

Yes. We regularly prepare feasibility studies for homeowners, developers and investors looking to understand the development potential of a property or site.

This can include high-level layout options, planning policy review, density considerations, risk analysis and advice on likely project viability. Feasibility studies are often the most cost-effective first step before progressing into full design and planning stages, particularly for new dwellings, flat conversions or complex planning sites.

Detailed Planning is a London-based architectural practice with over 15 years’ experience specialising in residential extensions, loft conversions, planning applications and development projects. We have helped secure more than 1,500 approved applications across London and the surrounding areas.

Our team includes Chartered Architectural Technologists registered with CIAT, led by Paul Cramphorn MCIAT. We also work alongside an ARB-registered architect within the practice, allowing projects to benefit from a collaborative architectural and technical approach.

You can view examples of our work in our approved projects and completed projects.

Our approach combines planning strategy, practical design experience and technical understanding from the earliest stages of a project. Rather than focusing purely on appearance, we consider planning risk, buildability, layout efficiency, natural light, property value and long-term usability together.

We use a mix of client-led and planning-led design, balancing your goals with what is realistically likely to achieve a successful outcome with the local authority. Our design process is structured to reduce uncertainty, avoid costly redesigns and guide clients through each stage clearly.

Yes. Detailed Planning carries professional indemnity insurance.

This is important when appointing a consultant to prepare drawings and provide professional advice.