Prior Approval for Larger Home Extension: A Complete 2025 Guide

For many homeowners, the idea of creating more space without moving house is very appealing. Larger home extensions have become a popular way to add value and improve living conditions. But one of the most common questions people ask is whether they need planning permission or if they can rely on prior approval for a larger home extension. This mechanism, also known as the Larger Home Extension Scheme, allows certain rear extensions to be built under permitted development rights, provided they meet specific requirements.

At Molecule Designs, we understand that the rules around home extensions and renovations can be confusing, especially when you're trying to figure out how big you can build, whether your neighbours can object, and how long the process will take. That’s why we’ve created this detailed guide to walk you through every step. From understanding the neighbour consultation scheme to knowing the limits on extension size and the conditions you must meet, we’re here to bring clarity and confidence to your project, before you even submit your application.

What Is Prior Approval for Larger Home Extensions?

Prior approval is part of permitted development rights introduced by the UK government to speed up smaller-scale housing projects. Under this scheme, homeowners can build certain single-storey rear extensions without applying for full planning permission. Instead, they must notify their local authority and allow neighbours the chance to comment.

This process is different from a planning application because it focuses mainly on the impact on neighbouring properties rather than the design of the extension itself. If the local authority raises no objections within the consultation period, or if objections are resolved, you can proceed with the project under permitted development rights.

The main benefit of prior approval is that it removes much of the uncertainty and delay of full planning permission. However, it still has strict limits, and not every property qualifies.

How Big Can You Build with Prior Approval in 2025?

The larger home extension scheme allows extensions that are bigger than the standard permitted development limits. For attached houses such as semis or terraced homes, you can extend up to 6 metres from the original rear wall of the house. For detached houses, the allowance increases to 8 metres.

Height is also regulated. The maximum height is 4 metres, and extensions cannot exceed the height of the original house’s roof eaves. This ensures the structure remains proportionate and does not overshadow neighbouring properties.

These size rules apply specifically to rear extensions. Side extensions and two-storey extensions fall under different planning categories and may require full permission.

Which Properties Are Excluded from the Larger Home Extension Scheme?

Not every property is eligible for prior approval. Homes in conservation areas, national parks, Areas of Outstanding Natural Beauty, and World Heritage Sites are excluded. Flats, maisonettes, and converted buildings also do not qualify for the scheme.

In addition, local councils can restrict permitted development rights through Article 4 Directions, which means you may need planning permission even if your extension fits within the general rules. Listed buildings always require consent, regardless of size.

Before applying, check with your local planning authority to confirm whether your property qualifies.

Key Conditions You Must Meet to Qualify

Even if your property is eligible, your extension must meet certain conditions:

• Height limits: Maximum 4 metres high, and eaves must match or be lower than the existing property.

• Boundary restrictions: Extensions closer than 2 metres to a boundary must have a maximum eaves height of 3 metres.

• Materials: The extension must use similar materials to the existing house for consistency.

• Restrictions: You cannot add verandas, balconies, or raised platforms.

Importantly, you must still comply with building regulations approval, which covers structural safety, insulation, drainage, and fire safety. Prior approval does not exempt you from these requirements.

How to Apply for Prior Approval for a Larger Extension

The application process is straightforward but requires careful preparation. You’ll need:

• Scaled architectural drawings of the proposed extension

• A site plan showing the property and boundaries

• A completed prior approval application form

Applications can be submitted via the Planning Portal or directly to your council. There is a small fee (typically £96). The local authority then has up to 42 days to make a decision. If they fail to respond in this time, approval is automatically granted.

What Happens After You Submit Your Application?

Once submitted, the council will notify neighbours and give them 21 days to raise objections. The council considers these comments along with planning guidance before making a decision.

If no objections are raised, or if they are not strong enough to justify refusal, the council issues written confirmation allowing the extension to proceed. If objections highlight valid concerns such as loss of light or overbearing impact, the council may refuse the application. 

What If My Neighbours Object?

Neighbours can object, but not every objection will carry weight. Councils consider only material planning concerns such as overshadowing, privacy, or noise impact. Personal opinions about design or dislike of the project are usually not valid grounds.

If your extension is refused due to objections, you can revise the design or submit an appeal. Many disputes can be avoided by discussing your plans with neighbours before submitting an application.

Can the Council Refuse My Prior Approval Application?

Yes. Councils can refuse prior approval if the extension causes significant harm to neighbours or breaches key conditions. Common reasons include:

• Excessive size for the setting

• Overlooking or loss of privacy

• Harm to the character of the area

If refused, you have the option to appeal, but this takes time and may delay your project.

When Can You Start Building Your Extension?

You can only start work once you have received written approval or the council’s 42-day deadline has passed with no response. Starting work before approval is granted could result in enforcement action.

Once approved, the work must begin within 3 years, otherwise, you’ll need to reapply. Always ensure your builder has the official approval notice before starting.

Prior Approval vs Full Planning Permission: Which Is Better?

While prior approval is quicker and less restrictive, it is not always the best option. If your property is in a sensitive location or your extension does not meet the scheme’s rules, full planning permission may be the safer route.

Prior approval works best for straightforward rear extensions on standard properties. For more complex designs, two-storey additions, or homes in restricted areas, planning permission is more suitable.

Costs of a Prior Approval Application

The application fee is £96, but the total cost is usually higher once you include:

• Architectural drawings

• Building regulations, drawings, and applications

• Structural engineer reports (if required)

While prior approval is cheaper than full planning permission, you should budget carefully to cover professional fees and building regulations compliance.

Final Checklist Before You Build

Checklist Item

What It Means

Why It Matters

Risks if Ignored

Written Approval from the Council

Ensure you have received official confirmation from your local planning authority that your prior approval application has been granted, or that the 42-day period has passed without refusal.

This is your legal right to build under the Larger Home Extension Scheme.

Starting without written approval can lead to enforcement notices, legal action, and even demolition of the extension.

Full Building Regulations Drawings Submitted & Approved

Submit detailed architectural drawings showing compliance with structural safety, fire safety, insulation, drainage, and other building regulations.

Ensures the extension is safe, energy efficient, and structurally sound.

Work may fail inspection, leading to costly changes, delays, or refusal of a completion certificate.

Party Wall Agreements (if required)

If your extension involves work on or near a shared boundary wall, you must notify neighbours under the Party Wall Act 1996.

Protects both you and your neighbours legally, preventing disputes over damage or shared structures.

Neighbours can take legal action, delay your project, or prevent work until agreements are in place.

Contractor Who Understands Permitted Development Rules

Hire an experienced builder familiar with prior approval rules and building control processes.

Reduces mistakes, avoids non-compliance, and ensures smooth communication with inspectors.

Inexperienced contractors may build outside limits, invalidating your approval and risking refusal or demolition.

Budget for Professional Fees

Factor in architect fees, structural engineer costs, and application fees beyond just construction costs.

Prevents unexpected expenses and keeps your project financially realistic.

Running out of funds midway can halt the project, leaving incomplete or unsafe work.

Insurance & Warranties

Ensure both you and your contractor have adequate site insurance and guarantees for workmanship.

Provides protection if issues arise during or after construction.

Without cover, you may face personal liability for accidents, damage, or defects.

Neighbour Communication

Keep neighbours informed about timelines and disruptions, even if no objections were raised.

Maintains good relationships and can reduce complaints during construction.

Poor communication can lead to disputes, complaints to the council, or strained neighbour relations.

Before breaking ground, make sure you have:

• Written approval from the council

• Full building regulations drawings submitted and approved

• Are any required party wall agreements in place

• A contractor who understands the permitted development rules

This ensures your extension runs smoothly without legal or technical issues.

Before You Build: What to Remember About Prior Approval Extensions

The prior approval process for larger home extensions offers homeowners a quicker and simpler way to extend their homes compared to full planning permission. However, it comes with strict rules, property exclusions, and a neighbour consultation requirement.

By understanding the eligibility criteria, size limits, and application steps, you can avoid mistakes that lead to refusals or disputes. If you’re unsure about your project, working with professionals like architects and planning consultants can make the process far easier.

With the right preparation, you can build a larger home extension that complies with the law, adds value to your property, and enhances your living space.