How Much Can I Extend My Garage Without Planning Permission UK

Extending a garage is an increasingly popular home improvement choice in the UK. Many homeowners want extra storage, a workshop or even a home gym and their existing garage provides a convenient base. Before commencing such work however it is essential to understand the planning rules. You may not always need full planning permission, especially if your proposal falls within permitted development rights. This article explains in detail how much you can extend your garage without planning permission, the key size and placement limits, additional requirements and common pitfalls.

Understanding Permitted Development Rights

Permitted development rights allow certain building works to be carried out without submitting a full planning application to the local authority. These rights stem from the Town and Country Planning (General Permitted Development) Order and apply in England under specified conditions. Bosaco Ltd+4GOV.UK+4GOV.UK+4

For a garage extension these rights mean that in many cases you can extend the building without applying for planning permission as long as your extension meets all of the relevant criteria. It is very important to emphasise that just because an extension is feasible does not guarantee it will qualify under permitted development. Each case must meet all conditions and any local restrictions must also be considered.

Key Size and Placement Limits for Garage Extensions

When working out how much you can extend your garage without planning permission you need to consider several dimensions and rules. These include the footprint in terms of land coverage, height limits, location in relation to the house and boundaries, and use of the extension.

Land Coverage and Footprint

One of the primary restrictions is that the total area of all outbuildings, extensions and the original house must not cover more than half of the land around the original house. The term “original house” generally means how the house was first built or existed on 1 July 1948, whichever is later. GOV.UK+2permitted-development.co.uk+2

In practical terms this means you must calculate the total external floor area of your house as originally built plus all outbuildings and extensions around it. If your garage extension will push that coverage over 50% of the land around the house then permitted development rights are no longer valid and planning permission will be required.

Height Restrictions

For permitted development to apply, an extension must usually be single storey and must respect specific height limits:

• A detached or attached garage extension with a dual-pitched roof must not exceed 4 metres in height. dencroftgarages.co.uk
• For any other roof type (flat, mono-pitch, hipped) the maximum height is 3 metres. planningportal.co.uk+1
• If the extension is within 2 metres of a boundary then the maximum height is reduced to 2.5 metres. planningportal.co.uk+1

These height limits apply to the extension itself. If your existing garage is already tall, the extension must not increase the overall height beyond the allowable limit if you wish to remain within permitted development.

Location Relative to the House and Boundaries

Additional rules relate to where the extension is placed in relation to your house and its boundaries. Key points are:

• The extension must not be forward of the principal elevation of the house that faces a highway. That means you cannot build the extension further towards the street than the front face of your house without planning permission. planningportal.co.uk+1
• If the extension is located within 2 metres of the boundary of the property, or within 1 metre of the house if the garage extension counts as part of the property boundary, then certain more restrictive limits apply (for example the 2.5m maximum height rule).
• The roof must not extend beyond the height of the existing house eaves if it is a rear extension and still fall under permitted development for adding a storey (though that is less commonly allowed for garages). resi.co.uk+1

Use and Purpose

While you may be extending a garage, how you use that extension matters. Under permitted development, the extension must remain ancillary to the house – in other words it should be used in connection with the main dwelling (for storage, parking, hobby use, etc) rather than as a separate dwelling unit or commercial premises. If the use changes materially then you may need full planning permission. Gillies & Mackay+1

How Depth of Extension is Treated

While much of the guidance focuses on height and land coverage, homeowners often ask: how far out or how much deeper can I extend my garage without planning permission? The rules differ slightly depending on whether it is a rear extension versus a side extension, and whether the garage is attached or detached.

Some guidance notes that for houses the maximum rear extension under permitted development may be up to 8 metres for detached properties and up to 6 metres for other types of house. While this rule is often cited for general home extensions, similar logic can apply to garage extensions, especially when they form part of the main dwelling and count as a rear extension. resi.co.uk+1

However, if your garage is detached, or if the extension is side-oriented rather than rear facing, the permitted development rights may not apply in the same way and full planning permission may be required. For example, when the garage extension is at the side of a property and visible from a highway, permitted development may be restricted. SWJ Consulting+1

Additional Considerations and Restrictions

Even if you stay within the size limits, other factors can mean that planning permission is required. These include: designated land, lost permitted rights, ultra large footprint, or change of use.

Local Restrictions and Designated Land

If your property is in a conservation area, national park, World Heritage Site, an Area of Outstanding Natural Beauty, or in the Norfolk or Suffolk Broads then the general permitted development rules may be more restricted. In those areas you may need full planning even for modest extensions. permitted-development.co.uk+1

Also, some homes have had permitted development rights removed via an Article 4 direction, meaning you have to apply for planning permission even when your extension would normally qualify. Checking with your local authority is essential. Reddit+1

Existing Size of Garage and Extensions

If your garage already exists, or if you have previously added extensions or outbuildings, those count towards the total coverage limit of half the land around the original house. For example, if you already have a large garage and you wish to extend it further, you may already be at, or close to, the 50% coverage limit and permitted development may not apply. permitted-development.co.uk+1

Changing the Use or Adding a Storey

If you plan to convert the garage extension into living space, or add a storey above it, then permitted development rights may not apply and full planning permission will usually be needed. In particular detached garages rarely allow the addition of a first floor under permitted development rules without permission. resi.co.uk+1

Practical Guidance on How Much You Can Extend

Putting the rules into practical terms, if you have a garage attached to your house and you wish to extend it to the rear, under permitted development you might typically be able to extend by around 6 metres if the house is not detached and up to around 8 metres if it is detached – assuming the extension remains single storey, is below the height limits, does not exceed 50% land coverage and all other rules are met. resi.co.uk+1

Here is an example scenario:
Imagine you have a semi-detached house with an attached garage and you want to deepen the garage by 5 metres to provide a workshop space. The extension will remain single storey, the roof height will be 3 metres, it will be at the rear of the house, and it will occupy a footprint well within 50% of the land. If the property is not in a conservation area and permitted development rights have not been removed, then you might proceed without full planning permission.

By contrast if that same extension sought to extend by 10 metres, or add a first floor, or build at the front of the garage, or increase height above 4 metres, then you would need to apply for planning permission.

Why It Matters to Check Before You Build

Failing to check whether your extension falls under permitted development can lead to significant issues. If you build without permission when it is required the local authority may serve an enforcement notice requiring the removal of the extension or alterations at your cost. It may also affect resale of the property, with buyers’ solicitors flagging the absence of proper approval.

Even when planning permission is not needed, it is strongly recommended to apply for a Certificate of Lawful Development. This certificate provides proof that your work was carried out lawfully and helps avoid problems if you sell the property later. resi.co.uk+1

Building Regulations Still Apply

Important to emphasise: even if your extension does not require planning permission, you still must comply with building regulations. These cover structural stability, insulation, fire safety, damp proofing, electrical work, and ventilation. Your local building control department should be notified before work begins. Failure to comply may affect insurance and resale value. resi.co.uk+1

Summary

In summary:
You can extend your garage without planning permission in the UK provided your extension falls under permitted development rights. That means your extension must be single storey, no more than 4 metres high for a dual-pitched roof (3 metres for other roofs), the extension must not cover more than 50 percent of the land around the original house, must not be forward of the principal elevation facing the road, and must remain ancillary in use. If the garage is within 2 metres of a boundary then height must not exceed 2.5 metres. Extensions deeper than around 6 to 8 metres may require full planning permission especially if they are side additions or have a first floor.

Because the rules are detailed and may vary based on local restrictions, it is essential to verify with your local planning authority or seek professional advice. Obtaining a Certificate of Lawful Development may also be wise for future protection.

If you would like, I can check the specific rules for your local authority in your postcode or draw up a checklist of steps to ensure your extension meets permitted development rights.