Planning an extension, a loft conversion, or a bigger project on your London home? Before you get too far into design, one question needs answering: do you need planning permission? In London the answer is less straightforward than elsewhere in the country, because the capital layers on extra rules — conservation areas, Article 4 directions, and stricter local constraints — that catch a lot of homeowners out.
This guide clears it up in plain English. We’ll explain the difference between planning permission, permitted development and Building Regulations (the three things people constantly mix up), what you can usually do without a full application, when you genuinely need permission, what makes London different, and how the structural side of your project fits in. By the end, you’ll know how to approach your project the right way round.
Planning permission vs. permitted development vs. Building Regs
Let’s untangle the three separate systems first, because getting these straight saves enormous confusion:
| System | The question it answers | Who’s involved |
|---|---|---|
| Planning permission | Am I allowed to build this? (size, appearance, impact on neighbours and area) | Local planning authority (your borough) |
| Permitted development | Can I do this without a full application? (rights granted automatically for certain works) | Usually no application — but confirm scope |
| Building Regulations | Is it built safely and correctly? (structure, insulation, fire, drainage) | Structural engineer + Building Control |
The crucial point: these are independent. A project can fall under permitted development (no planning application needed) yet still require Building Regulations approval — including structural calculations for beams and foundations. Never assume that “no planning permission needed” means “no approvals needed.”
What is permitted development — and what it covers
Permitted development rights allow certain home improvements without a full planning application, provided they stay within set limits. Broadly, and subject to conditions, these can include:
- Single-storey rear extensions within size and height limits.
- Loft conversions within volume allowances (and subject to appearance rules).
- Some outbuildings, porches, and internal alterations.
- Certain changes that don’t materially alter the external appearance.
But — and this matters hugely in London — permitted development rights are frequently restricted or removed in the capital. Flats and maisonettes generally don’t have the same rights as houses, and as we’ll see, whole areas have their rights curtailed. Even where rights apply, the limits (on depth, height, materials and coverage) are specific, so it’s always worth confirming your exact scope rather than assuming.
A useful safeguard is a Lawful Development Certificate — an optional application that gives you formal confirmation that your project is lawful permitted development. It’s not planning permission, but it’s valuable proof for the future, especially when you sell.
When you do need planning permission
You’ll generally need full planning permission when your project:
- Exceeds permitted development limits — a larger or deeper extension, or additional storeys.
- Is on a flat or maisonette (which typically lack the permitted development rights houses enjoy).
- Affects a listed building (where you’ll also likely need listed building consent).
- Sits in a conservation area or other designated area where rights are restricted.
- Falls under an Article 4 direction that has removed permitted development rights (common in London).
- Changes the use of a building, or significantly alters its appearance or impact on neighbours.
Because London boroughs vary and local constraints are common, the safest approach is to check with your borough’s planning department early, or have your designer or architect confirm the route before you invest in detailed plans.
What makes London different
London homeowners face several extra layers that homeowners elsewhere often don’t:
- Article 4 directions. These remove specific permitted development rights in defined areas — meaning work that would be automatic elsewhere needs a full application here. They’re widespread across London boroughs.
- Conservation areas. London has a very high concentration of them, bringing tighter controls on appearance, materials, and even some works that are normally permitted.
- Listed buildings. The capital’s rich period stock means many homes are listed, requiring listed building consent alongside planning.
- Borough-by-borough variation. Each London borough is its own planning authority with its own local policies and interpretation, so rules and expectations differ across the city.
- Density and neighbour impact. In tightly packed streets, issues like overlooking, loss of light and massing carry more weight in planning decisions.
The takeaway: never assume London follows the national default. What’s permitted in a suburban home elsewhere may need a full application — and careful design — in a London conservation area.
The planning application process, step by step
- Pre-application checks. Confirm whether you need permission at all, and consider a pre-application enquiry with your borough for larger or sensitive projects.
- Design and drawings. Your architect or designer prepares existing and proposed drawings.
- Submit the application. Usually via the national Planning Portal, with the borough’s fee and supporting documents.
- Consultation and determination. The borough consults neighbours and assesses the application; a decision typically takes around 8 weeks for householder applications (longer for complex cases).
- Decision. Approval (often with conditions), or refusal (which you can amend and resubmit, or appeal).
- Then Building Regulations. Planning permission is only half the story — you still need Building Regulations approval, including the structural design, before and during the build.
Where structural engineering fits in
Planning permission decides whether you can build; structural engineering and Building Regulations decide whether it stands up safely — and they’re required regardless of whether your project needed planning permission or fell under permitted development.
Once your project’s form is settled, a structural engineer produces the calculations and drawings your build depends on: beam design for removing walls, foundation design suited to your ground, and the structural elements for extensions and loft conversions. These form part of a Building Regulation Approval Package that Building Control signs off. Getting the structural engineer involved early — even during design — helps ensure what you’re seeking permission for is actually buildable and cost-effective.
Common mistakes London homeowners make
- Assuming permitted development applies. In London, Article 4 directions and conservation areas frequently remove those rights.
- Confusing planning with Building Regs. No planning permission needed ≠ no approvals needed; the structural and safety side still applies.
- Starting the build before all approvals are in place. Unauthorised work can mean enforcement action or costly rework.
- Leaving the party wall process late. For terraces and semis, the Party Wall Act often applies and has notice periods that add time.
- Skipping the structural engineer until the last minute. Early input avoids designs that are impractical or expensive to build.
Conclusion & next step
Planning permission in London rewards doing your homework early. Understand whether your project falls under permitted development or needs a full application, factor in the capital’s extra layers — Article 4, conservation areas, listed buildings and borough variation — and remember that whatever the planning route, you’ll still need Building Regulations approval and proper structural design to build safely and legally.
That’s where we come in. At Bolt Structures, our chartered structural engineers provide the calculations, foundation and beam designs, and Building Regulation packages that turn an approved plan into a safe, buildable reality — across West London, Harrow, Hemel Hempstead and the surrounding areas.
Ready to move your project forward? Get a free quote or explore our extensions service — tell us what you’re planning and we’ll advise on the structural design and approvals your build will need, usually the same day.
