Loft Conversion Types Explained: Dormer, Hip-to-Gable & Mansard

A rear extension is one of the most popular ways to add space to a London home. Whether you are looking to create an open-plan kitchen-diner, a larger living area, or a home office, a well-designed rear extension can transform how you use your property — and add significant value.

The first question most homeowners ask is: do I need planning permission? The answer depends on the size, height, and position of the proposed extension, and whether your property is in a conservation area or is a listed building. Many single-storey rear extensions fall within Permitted Development rights, meaning no formal planning application is required — but there are strict limits on depth, height, and materials.

For a detached house, a single-storey rear extension can extend up to 4 metres beyond the original rear wall under Permitted Development. For semi-detached and terraced houses, the limit is 3 metres. Under the Neighbour Consultation Scheme (sometimes called the Prior Approval process), these limits can be extended to 8 metres for detached houses and 6 metres for other house types — provided no objections are raised by adjoining owners.

If your extension exceeds Permitted Development limits, or if your property is in a conservation area, an Article 4 Direction area, or is a listed building, you will need to submit a full planning application to your London borough council. This involves preparing architectural drawings, a design and access statement, and sometimes additional reports such as a heritage impact assessment or a daylight and sunlight study.

Pre-application advice from the council can be invaluable before you submit. Many London boroughs offer a paid pre-application service where a planning officer will review your proposals informally and give feedback before a formal application is lodged. This can significantly improve your chances of a first-time approval.

At Megaplan, we manage the entire planning process on your behalf — from initial feasibility and design through to submission, council liaison, and decision notice. Our track record of first-time approvals across London boroughs including Lambeth, Southwark, Lewisham, Wandsworth, Hackney, and Islington reflects our understanding of local planning policies and design guidance.

Once planning permission is granted, you will also need Building Regulations approval before work begins. Building Regulations cover structural integrity, fire safety, insulation, ventilation, and drainage — and are separate from planning permission. We prepare full plans submissions and liaise with the building control body throughout the construction process.

Many homeowners are surprised to learn that planning permission and Building Regulations are entirely separate approvals. You can have planning permission but still need Building Regulations approval before work begins — and in some cases (such as Permitted Development extensions), you need Building Regulations even though no planning application was required.

Building Regulations set minimum standards for the design and construction of buildings in England. For extensions, the key areas covered include: structural integrity (foundations, walls, floors, and roof); fire safety (escape routes, fire doors, smoke alarms); thermal performance (insulation to meet Part L energy efficiency requirements); ventilation (Part F); drainage and waterproofing; and electrical and plumbing installations.

There are two routes to Building Regulations approval. The Full Plans route involves submitting detailed drawings and specifications to the building control body before work starts. The building control officer reviews the plans and issues an approval notice. This is the route we recommend for most extension projects, as it gives you certainty before work begins and protects you if any disputes arise during construction.

The Building Notice route allows work to start without submitting full plans, with the building control officer inspecting the work at key stages. This route is faster but carries more risk — if the inspector requires changes, they must be made at the contractor's expense.

Since the Building Safety Act 2022, the regulatory framework for higher-risk buildings (those over 18 metres or 7 storeys) has been significantly strengthened. For most residential extensions in London, the changes most relevant to homeowners are the increased emphasis on the Golden Thread of information — maintaining accurate, up-to-date records of the building throughout its life.

At Megaplan, we prepare full plans Building Regulations submissions for all extension and loft conversion projects. We liaise directly with the building control body, respond to any technical queries, and attend site inspections to ensure your project achieves a completion certificate — the document you will need when you come to sell your property.

London has over 1,000 conservation areas — designated zones where the character and appearance of the area is considered worth preserving or enhancing. If your property is in a conservation area, the rules around extensions and alterations are stricter than for properties outside these zones.

The most significant difference is that Permitted Development rights are restricted in conservation areas. Works that would normally be allowed without planning permission — such as rear extensions, roof alterations, and cladding — require a planning application in a conservation area. This means that even a modest single-storey rear extension will need formal approval from your London borough council.

Conservation area planning applications are assessed against the council's Conservation Area Appraisal and Management Plan, which sets out the special character of the area and the design principles that new development should follow. Key considerations include the choice of materials (brick, stone, render, and roof tiles should match or complement the existing building and the character of the area), the scale and massing of the extension, and the impact on the streetscene and on neighbouring properties.

Pre-application advice is particularly valuable for conservation area projects. A pre-application meeting with the council's conservation officer can help you understand what is likely to be acceptable before you invest in detailed design work. At Megaplan, we have extensive experience of working in London conservation areas and can advise on the design approach most likely to secure approval.

If your property is a listed building as well as being in a conservation area, you will also need Listed Building Consent for any works that affect the character of the building — including internal alterations. Listed Building Consent is a separate application from planning permission and requires a heritage impact assessment prepared by a suitably qualified professional.

We have successfully secured planning permission for extensions and alterations in conservation areas across London, including projects in Lambeth, Southwark, Islington, and Hackney. Our approach combines a thorough understanding of local planning policy with high-quality architectural design — giving your application the best possible chance of a first-time approval.