How to Get Planning Permission for a House Extension in London
Planning permission for a house extension in London isn't automatic — but it's more manageable than many homeowners expect. Understanding when you need it, how the process works, and what affects the outcome helps you avoid unnecessary delays and costs.
Do You Need Planning Permission?
Not all extensions require full planning permission. The Permitted Development (PD) rights regime allows many common extension types to proceed without a formal application, subject to specific size and location limits.
Permitted Development for rear extensions typically allows: single-storey extensions up to 4m (detached houses) or 3m (semi-detached and terraced) behind the original rear wall under the standard PD limit; up to 8m (detached) or 6m (semi-detached and terraced) under the larger home extension scheme, subject to neighbour consultation; and side extensions up to half the width of the original dwelling, under 4m in height for single-storey.
However, PD rights are removed in several situations: conservation areas and Article 4 directions restrict PD rights significantly; flats and maisonettes have no residential PD rights; properties where previous extensions have used up the PD allowance may need permission for further works; and houses converted from other uses may have conditions attached that restrict PD.
A Lawful Development Certificate (LDC) from the local planning authority gives you formal written confirmation that your proposed works are lawful under PD. This typically costs £103 for a householder application and takes 8 weeks. For most clients, it's worth getting one even when you're confident the works are PD — it's the evidence base if you ever sell.
When You Need Full Planning Permission
Where PD rights don't apply, or where you want to exceed PD limits, a full householder planning application is required. The process involves: preparing plans and a design-and-access statement or planning statement if required; paying the application fee (currently £258 for householder extensions); council statutory determination within 8 weeks (though many London boroughs take longer); consultation with neighbours; and potentially pre-application advice from the planning officer if the project is complex.
What Affects the Decision
Local planning policies. Each London borough has its own Local Plan with policies on residential extensions. Some boroughs are more restrictive than others about materials, scale, and relationship to neighbouring properties.
Impact on neighbours. Overshadowing, loss of outlook, and loss of privacy are the most common grounds for neighbour objection and refusal. The 45-degree rule (an informal guideline used by many planning officers) assesses whether a proposed extension would overshadow a neighbouring window.
Design quality. Extensions in conservation areas face stricter scrutiny on materials and appearance. Even outside conservation areas, some boroughs require new extensions to use matching or complementary materials.
Trees. Trees protected by a Tree Preservation Order (TPO) or within a conservation area cannot be removed or significantly pruned without consent. Extensions that would affect protected tree roots may require an arboricultural impact assessment.
How RCB Supports the Planning Process
RCB coordinates with architects and planning consultants to support clients through the planning process as part of our design-and-build scope. We provide practical input on how design decisions affect planning risk, construction feasibility, and cost — so that the design developed for planning is one that can actually be built efficiently.
07359 872594 | contact@rcbgroup.co.uk | www.rcbgroup.co.uk