Typical Extension Sizes Approved Near You: What Matters Most

Planning rules tell you what you can build, but what actually gets approved in your area often tells a different story. Your neighbours' extensions might be larger or smaller than what the rules suggest is possible. The real sizes of extensions that get approved near you matter more than national policies because local planning officers, site conditions, and neighbourhood patterns heavily influence what councils will accept.

Looking at typical extension sizes in your area gives you a practical starting point for your own project. A 6-metre rear extension might be allowed under permitted development rules, but if most approved extensions on your street are only 4 metres deep, there's probably a good reason. Understanding these local patterns helps you plan an extension that's more likely to succeed.

This guide shows you how to research actual approved extensions near you and why this matters for your project. You'll learn how to balance planning rules with local reality and make smarter decisions about your extension size.

Key Takeaways

• Actual approved extension sizes in your area often differ from what national planning policies allow

• Local planning patterns and site conditions influence what gets approved more than standard permitted development rules

• Researching nearby extensions helps you plan a project that's more likely to gain approval

Understanding Typical Extension Sizes Approved Near You

The size of extension you can build depends on national permitted development limits and how your local planning authority interprets them. Different property types have different allowances, and what gets approved in your neighbourhood often reflects local priorities around character and density.

Key Size Limits for Extensions

For detached houses, you can extend up to 8 metres beyond the rear wall under permitted development rights. Semi-detached and terraced houses have a reduced limit of 6 metres. Single-storey rear extensions can be built under the General Permitted Development Order (GPDO) without a planning application if they meet height restrictions of 4 metres maximum or 3 metres when built within 2 metres of a boundary.

Two-storey extensions face stricter controls. You cannot extend beyond 3 metres from the rear wall, and the extension cannot be higher than the existing roof. Side extensions must not exceed half the width of the original house and typically cannot extend beyond the building line facing a road.

How Local Variation Impacts Approval

Your local planning authority can remove or modify permitted development rights through Article 4 directions in conservation areas or locations with specific planning concerns. This means extensions that would normally not need planning permission might require a full planning application in your area.

Some councils apply stricter interpretations of design guidelines even within permitted development limits. They may scrutinise materials, window placement, and roof styles more carefully based on local character assessments. Neighbouring objections carry more weight in certain areas, particularly in historic districts or areas with consistent architectural styles.

Why Size Regulations Exist

Size limits prevent extensions from overwhelming original properties and neighbouring homes. They protect access to natural light for adjacent properties and maintain reasonable garden space. The regulations balance your need for additional space against the impact on your street's character and your neighbours' enjoyment of their properties.

The GPDO sets baseline protections that apply across England. These rules ensure extensions do not create overbearing structures or lead to excessive site coverage. Local planning authorities use these standards to preserve neighbourhood character whilst allowing homeowners flexibility to adapt their properties to changing needs.

Permitted Development Extension Sizes: What You Can Build

Under permitted development rights, detached houses can extend up to 8 metres to the rear single-storey, whilst semi-detached and terraced properties are limited to 6 metres. Side extensions are restricted to half your property's original width, and two-storey additions require planning permission in most cases.

Single-Storey Rear Extensions: Standard and Larger Limits

Your single-storey rear extension allowance depends on whether you use standard permitted development or the larger home extension scheme.

Under standard permitted development, you can build 4 metres from the rear wall if you own a detached house. For semi-detached, terraced, or end-of-terrace houses, the limit drops to 3 metres. The extension cannot exceed 4 metres in height, and the eaves height must not go above 3 metres.

The larger home extension scheme doubles these allowances. Detached houses can extend 8 metres, whilst all other house types can go up to 6 metres. This scheme requires prior approval from your local council, which involves notifying your neighbours and paying a fee of approximately £240.

Your extension must stay within half the land around your original house. Materials should match or complement your existing property. The measurement starts from your house as it was first built, so previous extensions count against your total allowance.

Side Extensions and Side Return Extensions

Side extensions under permitted development face strict width restrictions to prevent overdevelopment. Your single-storey side extension cannot be wider than half the width of your original house.

Side return extensions, popular in terraced properties, must meet this same width rule. The extension height is limited to 4 metres for single-storey builds. Any multi-storey side extension requires full planning permission regardless of size.

Windows on side elevations need special attention. They must use obscure glazing or have opening parts positioned at least 1.7 metres above floor level to protect your neighbours' privacy. Standard clear glass windows facing neighbouring properties will invalidate your permitted development rights.

If you live in a conservation area, your permitted development rights for side extensions are usually removed. You'll need to submit a planning application instead.

Double and Two-Storey Extension Size Rules

Two-storey extensions have significantly tighter restrictions under permitted development rights. Your extension cannot project more than 3 metres beyond the rear wall, regardless of property type.

The extension must not exceed the height of your existing roof. The eaves height cannot be higher than the eaves of your current house. Your roof pitch should match the existing property where the extension joins the main building.

Double storey rear extensions are only permitted development if they're set back from side boundaries. Any part of the extension within 7 metres of a boundary facing a road or footpath cannot exceed 4 metres in height. Multi-storey side extensions always require planning permission.

All your extensions combined, including outbuildings, cannot cover more than 50% of your total land area. This rule applies to everything built since the original house was constructed.

Loft Extensions and Height Restrictions

Loft conversions under permitted development must not increase your roof height by more than 150 millimetres. This tight restriction means most loft extensions involve changing the roof shape rather than raising it.

Your loft extension volume is limited to 40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached properties. The extension must be set back at least 200 millimetres from the eaves on all sides. You cannot add balconies or verandas through permitted development.

Roof windows must be non-opening or have opening parts at least 1.7 metres above the floor. Side-facing dormers require planning permission. Materials should match your existing roof where possible.

The highest part of your enlarged roof cannot extend beyond the highest part of your current roof. If you live in a conservation area or national park, you'll need planning permission for any loft conversion regardless of size.

Making the Most of Prior Approval and the Larger Home Extension Scheme

Prior approval lets you build larger single-storey rear extensions without full planning permission, but you need to notify your council first. The process involves neighbour consultation and specific size limits that depend on your property type.

Neighbour Consultation Scheme Explained

When you plan a larger extension, your local planning authority must consult your neighbours before granting prior approval. This gives adjacent properties 21 days to review your plans and raise any concerns about how the extension might affect their property.

The council will send notification letters to neighbours who share a boundary with your property. Neighbours can object based on specific issues like loss of light, privacy concerns, or visual impact. However, their objections don't automatically stop your extension.

Your local planning authority reviews any objections and decides whether to grant prior approval. They focus on the impact to neighbouring amenity rather than design preferences. If no objections arrive within 21 days, the process typically moves forward more quickly.

Steps in the Prior Approval Process

You start by submitting a prior approval application to your local planning authority. Your application needs a location plan, existing and proposed elevations, floor plans, and a written description of your proposed extension.

The council has 42 days to make a decision from the date they receive your complete application. During this time, they'll assess whether prior approval is needed based on:

• Impact on neighbouring properties

• Design and external appearance

• Transport and highways considerations

You cannot start building until you receive approval or the 42-day period expires without a decision. Starting work early could result in enforcement action and may require you to remove the extension.

Larger Home Extension Scheme Restrictions

Your extension can project up to 8 metres from the rear wall if you have a detached house, or 6 metres for all other house types. These measurements apply to the original house as it stood on 1 July 1948.

The extension must stay within specific limits:

• Maximum height of 4 metres

• Must not cover more than half the land around the original house

• Side walls cannot exceed 3 metres in height

• Materials must be similar in appearance to the existing house

Previous extensions by you or former owners may have already used up some or all of your permitted development rights. Check your property's history before assuming you qualify for the full allowance.

Limits, Exemptions, and Special Cases

Permitted development rights don't apply everywhere or in every situation. Some properties face additional restrictions that override the standard limits, whilst others require extra approvals beyond planning permission.

Article 4 Directions and Conservation Areas

An Article 4 direction removes some or all permitted development rights in specific areas. Your local planning authority issues these directions to protect the character of neighbourhoods, conservation areas, or other significant locations.

If your property sits within an Article 4 direction area, you'll need planning permission for extensions that would normally be allowed under permitted development. This often affects side extensions, rear extensions, and changes to the front of your house.

Conservation areas automatically restrict certain rights. You cannot build side extensions under permitted development in these areas. All extensions on Article 2(3) designated land face stricter rules, including conservation areas, National Parks, Areas of Outstanding Natural Beauty, and World Heritage Sites.

Check with your local planning authority before starting any work. They maintain maps showing where Article 4 directions apply. Estate agents and solicitors should disclose this information when you buy a property, but it's worth verifying independently.

Listed Buildings and Additional Consents

Listed buildings require listed building consent for most alterations, even minor changes that would normally be permitted development. This consent sits alongside planning permission as a separate requirement.

You need listed building consent for work affecting the building's special architectural or historic interest. This includes both external and internal changes. Extensions always require this consent, regardless of size.

The application process involves detailed drawings and heritage statements. You must demonstrate how your extension respects the building's character. Listed building consent typically takes longer than standard planning applications because conservation officers need to assess the impact carefully.

Properties within the curtilage of a listed building also face restrictions. Outbuildings, walls, and other structures built before 1948 might be considered part of the listing.

Curtilage and Cumulative Extensions

Curtilage means the enclosed land immediately surrounding your house. Permitted development rules state that extensions and outbuildings cannot cover more than half the area of land around the original house.

This 'half rule' includes all buildings, not just your proposed extension. Previous extensions, garages, sheds, and conservatories count towards this limit. You must calculate the total coverage based on the original house as it was first built or as it stood on 1 July 1948.

Cumulative extensions create complications when calculating permitted development limits. If a previous owner built a four-metre rear extension, you cannot add another four-metre extension under permitted development. The total enlargement matters, not just your current proposal.

Measure carefully and account for all existing structures. If you exceed the half coverage rule, you'll need planning permission regardless of other dimension limits.

From Policy to Practice: Why Extension Sizes Matter More Than the Rules Alone

Understanding permitted development limits is one thing, but what gets approved in your area often depends on practical considerations that go beyond the policy itself. Your neighbour's concerns, future buyers' perceptions, and how your local planning authority interprets the rules can all affect whether your extension succeeds.

Neighbour Impact, Privacy, and Amenity

Your extension might comply with every technical requirement, but if it creates privacy issues or blocks light to neighbouring properties, you'll likely face objections. Planning authorities assess the amenity impact on surrounding homes, even for extensions that fall within permitted development limits.

A two-storey rear extension that sits 3 metres from the boundary might be technically allowed, but windows facing directly into your neighbour's bedroom will raise concerns. Similarly, an 8-metre single-storey extension on a detached house could overshadow a neighbour's garden for most of the day.

Local planning authorities often refuse applications or withdraw permitted development rights when neighbours demonstrate genuine harm. This happens even when you've followed the rules precisely. If you're planning something close to the limits, consider hiring a planning consultant to assess potential objections before you start.

Compliance and Future Saleability

Extensions built without proper oversight can create problems when you sell your property. Buyers' solicitors will request evidence that work was completed legally, typically through building control certificates or a lawful development certificate.

If you cannot prove your extension was built under permitted development or with planning permission for an extension, buyers may withdraw their offers or demand price reductions. Some mortgage lenders refuse to finance properties with undocumented extensions.

The cost of obtaining a lawful development certificate retrospectively ranges from £200 to £500, but there's no guarantee your local planning authority will issue one. In some cases, you might need to apply for retrospective planning permission or even remove the extension entirely.

Planning Authority Interpretation

Different local planning authorities interpret permitted development rules differently, particularly around measurements and boundary treatments. What counts as the "original house" or where you measure height from can vary between councils.

Some authorities take a stricter view on materials, requiring closer matches to existing finishes than the rules technically demand. Others focus heavily on neighbourhood character, even when assessing permitted development applications. Your local planning authority maintains records of previous decisions in your area, which provide useful guidance on their typical approach.

Beyond Size: Essential Legal and Technical Requirements

Getting approval for your extension size is just the first hurdle. Your project must also comply with Building Regulations standards and potentially require formal agreements with neighbours, especially when working near shared boundaries.

Building Regulations and Completion Certification

Building Regulations set mandatory standards for structural integrity, fire safety, energy efficiency, and accessibility. These apply to all extensions regardless of whether you need planning permission. You must submit a Building Regulations application to your local authority or use an approved inspector before starting work.

The regulations cover crucial aspects like foundation depth, wall insulation, window sizes for ventilation, and electrical safety. For example, new extensions must meet current thermal efficiency standards, which are significantly stricter than older buildings. You'll also need proper drainage connections and safe staircase dimensions if adding a second storey.

Upon completion, you'll receive a completion certificate. This document proves your extension meets legal standards. Without it, you may face serious issues when selling your property or applying for remortgages.

Party Wall Agreements and Boundary Considerations

If your extension sits on or within three metres of a boundary shared with neighbours, you'll likely need a party wall agreement. This legal requirement applies even if you have planning permission and good relations with your neighbours.

You must serve a party wall notice at least two months before starting work. This gives neighbours time to review your plans and appoint a surveyor if they wish. The agreement protects both parties by documenting the existing condition of properties and establishing how any damage will be resolved.

Working directly on a shared wall requires even stricter protocols. You cannot simply assume consent. The Party Wall Act 1996 gives neighbours specific rights to review structural calculations and building methods.

Frequently Asked Questions

Homeowners commonly ask about specific measurements, approval rates, and how their neighbours' builds affect their own applications. Understanding these practical details helps you plan an extension that fits both your needs and local standards.

What are the standard dimensions for home extensions that generally receive approval in residential areas?

Single-storey rear extensions typically gain approval at 3 metres for terraced or semi-detached homes and 4 metres for detached properties under permitted development. These measurements apply from the original rear wall of your house.

Two-storey extensions face stricter limits. They must not extend beyond the rear wall by more than 3 metres for any property type under permitted development rights.

Side extensions usually need to maintain a 7-metre gap between properties on semi-detached or detached homes. The extension cannot exceed half the width of the original house's plot.

How does the size of a proposed extension impact the likelihood of obtaining planning permission?

Extensions that stay within permitted development limits avoid the need for planning permission entirely. Going beyond these dimensions requires a full planning application, which faces closer scrutiny.

Larger extensions draw more attention from planning officers and neighbours. A 6-metre rear extension on a terraced house needs planning permission and will likely receive objections if it blocks light or views.

The 50% rule matters significantly. Extensions cannot cover more than half your property's original curtilage, including any previous builds. Exceeding this threshold almost guarantees a planning refusal.

What factors do local planning authorities consider when assessing the extensions' dimensions?

Planning officers examine how your extension affects neighbouring properties' access to natural light. A large side extension that casts shadows over next door's windows often faces rejection.

Your extension's height matters as much as its footprint. Buildings that exceed the original roofline or appear overbearing compared to surrounding properties raise concerns about visual impact.

Local authorities assess whether your extension maintains the street scene's character. In conservation areas or uniform housing estates, extensions must match existing architectural styles and proportions.

Could you detail the variations in permissible extension sizes in different types of residential zones?

Detached houses receive the most generous allowances. You can build 4 metres to the rear under permitted development and have more flexibility with side extensions.

Terraced and semi-detached properties face tighter restrictions. The 3-metre rear extension limit reflects concerns about cramped spacing and neighbour impact in denser housing.

Conservation areas and Article 4 directions remove many permitted development rights. These zones often require planning permission for any extension, regardless of size.

Flats and maisonettes have virtually no permitted development rights for extensions. You'll need planning permission for almost any structural addition to these properties.

Why is it important for homeowners to understand the size constraints before planning a home extension?

Knowing the limits saves you thousands in wasted architect fees and planning applications. Designing an extension that exceeds permitted development from the start means guaranteed delays and costs.

Size constraints directly affect your extension's functionality. A kitchen extension that falls 1 metre short of your ideal layout might not accommodate your planned island or dining area.

Understanding these rules helps you negotiate with builders and designers. You can spot when professionals propose unrealistic dimensions that will face planning rejection.

How might the size of a neighbouring property's extension influence future approval for your own?

A neighbour's approved extension doesn't guarantee approval for yours. Planning officers assess each application based on its specific impact, orientation, and relationship to surrounding properties.

Existing extensions can actually limit your options. If your neighbour built to the maximum allowed depth, planning officers may refuse a similar extension on your side to prevent a tunnelling effect.

Precedent matters in planning appeals. You can reference approved neighbouring extensions of similar size when arguing your case, though this doesn't override other planning concerns.