Top 10 Reasons London Extensions Get Planning Permission Refused

Why London Refuses So Many Extensions

According to GOV.UK planning statistics, England grants around 88–90% of householder planning applications. London boroughs consistently perform well below that average. A 2025 analysis by Planning Resource found that London boroughs accounted for seven of the ten local authorities in England with the lowest planning approval rates.

The reasons are structural. London has higher housing density than anywhere else in England, which means extensions have a greater impact on neighbours. Around a quarter of inner London properties sit within designated conservation areas, where the rules are substantially stricter. Many streets are subject to Article 4 directions that remove permitted development rights entirely. And London boroughs tend to apply their local design policies more rigorously than councils elsewhere.

The ten refusal reasons below cover the vast majority of refused householder applications in London. Each one is avoidable if you understand what planners are looking for and design accordingly from the start.

Overlooking is the most frequently cited reason for objection and one of the most common grounds for outright refusal. When a new extension has windows — or a flat roof that can be used as a terrace — that look directly into a neighbour's garden, bedroom, or main living space, planners will refuse it.

Most London boroughs apply a minimum separation distance before an overlooking impact is considered acceptable. The standard threshold, derived from the Greater London Authority's housing design guidance, is 18–21 metres between facing habitable room windows. Some boroughs apply the rule differently in more densely built-up areas, but the principle is consistent.

Loss of daylight and sunlight to a neighbouring property is a separate planning consideration from overlooking, and it is assessed differently. Planners use the BRE guidelines (Building Research Establishment document BR209) as the primary reference. Two tests are most commonly applied to extension applications:

Two-storey rear extensions are especially likely to trigger daylight objections from neighbours whose side-facing kitchen or living room windows are close to the shared boundary. Commissioning a daylight and sunlight assessment before submission — not after receiving objections — is standard practice for any two-storey scheme.

Overdevelopment is a catch-all planning term for a proposal that is considered too large relative to the plot, the house, or the surrounding area. In practice, it comes up in two related ways for extension applications.

The first is the 50% curtilage rule. Permitted development rules — and many local plans — state that extensions and outbuildings must not cover more than 50% of the land area of the original garden (the garden as it existed on 1 July 1948, or as originally built if later). This includes all extensions and outbuildings already built, not just the new proposal. If you have already added a garden room, a previous extension, and a large shed, a further rear extension may push total coverage over that threshold.

The second is proportionality. Even within the coverage limit, an extension that is clearly too large for the house — for instance, a single-storey rear extension that is nearly as wide as the house is deep, or a loft conversion that creates a roofline significantly larger than any comparable property on the street — will be refused as disproportionate.

Every London borough has design policies requiring that extensions are sympathetic to the character of the original building and the surrounding street. This is one of the most subjective refusal reasons, but it has consistent patterns in practice.

The most common design mismatch that leads to refusal is a flat-roofed extension on a property where the street pattern, neighbouring extensions, and local design guidance all indicate a pitched or lean-to roof is expected. This is especially common in outer London boroughs with Victorian and Edwardian terraces where the council has specific design guidance on roof forms.

Materials are a close second. Using render on a brick house in a brick terrace, or inserting uPVC window frames into a period property, will frequently attract a refusal reason citing harm to the character of the original building. Planners are also increasingly attentive to roof terrace additions on otherwise traditional properties.

Approximately 1,000 conservation areas exist across London's 33 boroughs — a significantly higher proportion than anywhere else in England. If your property is within one, the planning bar is materially higher.

The legal duty is to preserve or enhance the character or appearance of the conservation area. That is a positive obligation — it is not enough to show your extension will not actively harm the area. An application that is simply neutral is unlikely to satisfy the test unless the extension is genuinely invisible from the public realm.

Common refusal grounds in conservation areas include: incorrect roof materials (concrete tile instead of natural slate), use of standard uPVC windows instead of timber sliding sash, contemporary rear extensions that are visible from neighbouring properties or rear lanes, and loft conversions with dormer windows on principal elevations.

Conservation area appeals have a lower success rate than standard householder appeals. Getting the design right before submission is far more reliable than appealing a refused scheme.

If your property is a listed building, or if your proposed extension would affect the setting of a nearby listed building, the threshold for refusal is substantially lower than for a standard application.

For works to a listed building itself, you need Listed Building Consent in addition to planning permission. The council is required to treat any harm to the significance of a listed building as a very strong presumption against approving the scheme. Even proposals that would be perfectly acceptable on an unlisted Victorian terrace — a contemporary rear extension, for instance, or a flat-roof dormer — will typically be refused on a listed building unless the design is particularly sensitive and the case for harm is fully addressed.

The setting of a listed building is also protected. An extension to your unlisted property that would be directly visible from a listed building in the same terrace or on the adjacent street can still be refused on grounds of harm to the setting of that listed building.

Highway safety is a less common refusal ground for standard rear or loft extensions, but it becomes highly relevant for front extensions, side extensions close to the road, and any proposal that removes or reduces off-street parking on a car-dependent street.

The main issues are: obstructing visibility splays at the junction of the driveway and the road; reducing pedestrian footway width; blocking sightlines for drivers emerging from the property; and removing existing off-street parking without providing a replacement.

In practice, this refusal reason most commonly affects: front extensions that push toward the front boundary, garage conversions that remove the only off-street parking space on a street with high parking pressure, and side extensions that encroach on a side access used for pedestrians.

In inner London — where most properties have no off-street parking and residents use public transport — this reason is far less commonly cited for rear or loft extensions. Outer London boroughs are more sensitive to parking impact, particularly in areas with restricted permit zones.

Trees with Tree Preservation Orders (TPOs) are a significant planning consideration in London, particularly in outer boroughs with larger gardens. An extension footprint that falls within the root protection area of a protected tree will be refused unless a robust arboricultural impact assessment demonstrates the roots will not be damaged.

The root protection area is typically calculated as a circle with a radius 12 times the trunk diameter, measured at 1.5 metres above ground. For a mature tree with a 50cm diameter trunk, that is a 6-metre protection radius — which can easily cover a substantial portion of a rear garden in an inner London terrace.

Commission an arboricultural survey as part of the design process — not after planning is submitted. A tree officer can informally advise at pre-application stage whether the proposed footprint is likely to be acceptable. Shifting an extension by 1–2 metres to clear a root protection area is far cheaper than a refused application and redesign.

A substantial proportion of planning applications are returned at validation — before they are formally accepted and registered — because they are missing required documents or the drawings are inadequate. This is not a refusal on planning grounds, but it delays the process by weeks and increases the risk of a formal refusal if the application is submitted without proper preparation.

The most common documentation problems are: missing existing and proposed floor plans at a consistent scale (1:100 or 1:50); no site location plan at 1:1250; proposed elevations that do not match the floor plans in dimension; missing Design and Access Statement (required for conservation areas and listed buildings); and missing heritage statements where required.

Check your council's Local Validation Checklist before submitting. Every London borough publishes one and it sets out exactly what documents they require for householder applications, including any borough-specific additions. A missed document causes a delay of at least 2–4 weeks while the application is returned and resubmitted.

This refusal reason is less obvious than the others, but it accounts for a meaningful number of refused and invalid applications. It occurs when a homeowner submits a full planning application for something that does not actually require it — or, conversely, proceeds without any application for something that clearly does.

The most common version: submitting a full planning application for a single-storey rear extension that falls within permitted development limits. The council should in theory deal with this, but some authorities will refuse it on the grounds that the application type is wrong, or they will accept it and issue a grant that creates unnecessary complications for mortgage lenders and insurers compared to a Lawful Development Certificate.

The reverse problem: assuming that because something looks small it can be built without any permission, then receiving an enforcement notice years later. A neighbour's complaint can trigger an enforcement investigation at any time within 10 years of the works being completed — the 10-year enforcement rule means that building without permission is not a safe strategy even for works that have not been noticed.

How to Avoid Refusal

The majority of London extension refusals are preventable. Three things make the most difference.

What to Do If You Are Refused

A refusal is not the end. There are two main options: appeal the decision, or submit a revised application addressing the reasons for refusal.

Appealing a refusal

Householder planning appeals in England have a success rate of approximately 34%, according to Planning Inspectorate data for 2024/25. That means roughly one in three appeals against a householder refusal succeeds. The rate is higher where the refusal was on marginal grounds (for example, a design judgment rather than a clear policy breach) and lower where the refusal was based on an objective assessment of daylight impact or conservation area harm.

The appeal must be submitted to the Planning Inspectorate within 12 weeks of the refusal decision. Most householder appeals are decided by written representations — no hearing or inquiry is needed. The appeal inspector is independent of the local authority and can overturn the decision if they consider it was not justified by policy. You have one free attempt at a written representations appeal (no professional representation required, though it helps).

Revised application

Where the refusal reasons are design-based — overlooking can be fixed by repositioning windows, scale can be addressed by reducing depth or height — a revised application is often faster and more reliable than an appeal. If you submit a revised application within 12 months of the original decision, there is no application fee for the revised submission (for householder applications). You can submit both an appeal and a revised application simultaneously — this is a common strategy where the original design had merit but one specific issue caused the refusal.

The 10-Year Rule: Why You Should Not Simply Build Anyway

Some homeowners consider proceeding with refused works on the assumption that the council will not notice, or that after enough time passes the works will be immune from enforcement. This is a misunderstanding of how enforcement law works.

The enforcement time limit for unauthorised building operations (which includes extensions) is 10 years from the date the works were substantially completed. The council can serve an enforcement notice at any point within that window requiring the unauthorised works to be demolished and the site restored. If you ignore the notice, the council can enter the property, carry out the works itself, and recover the costs from you as a debt.

The 10-year period also creates problems when selling the property. Conveyancing solicitors will check planning status as part of due diligence, and an unauthorised extension will require either a retrospective planning application, a Certificate of Lawful Development (confirming the 10 years has passed), or indemnity insurance — all of which can delay or abort a sale.

The right response to a planning refusal is to appeal, revise, or accept the decision — not to build anyway and hope.

Summary

London's planning refusal rate for householder applications is significantly higher than the national average, but the vast majority of refusals come down to the same ten reasons. Overlooking, loss of daylight, overdevelopment, design mismatch, conservation area harm, listed building impact, highway concerns, tree protection, incomplete applications, and wrong application type together account for almost every refused extension scheme.

The single most effective thing you can do before submitting is to take pre-application advice from your council's planning service. The second most effective is to work with an architect who has specific experience with your borough's policies. Both investments are modest relative to the cost of a refusal, an appeal, a redesign, and months of delay.

If you have been refused, read the decision notice carefully, understand which reasons are addressable by design and which are matters of principle, and then decide whether to appeal, revise, or pursue a fundamentally different scheme.