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Planning Permission for a Home Extension: Step-by-Step Guide

Extending your home might sound straightforward—until you’re knee-deep in forms, unsure which rules apply or where to even begin. It’s not the most thrilling part of a build, but it’s the one that sets everything else in motion. So here’s how the process actually works—broken down in a way that makes it easier to get going without falling into the usual delays that end up costing more than they should.

Check if planning permission is required

Before you go any further, confirm whether your project even needs planning permission. A good number of extensions fall under what’s known as ‘permitted development’, which allows certain works to be carried out without formal consent. But if you’re looking at a double-storey extension in semi-detached house plans, you’ll likely need approval. The key factors include height, footprint, proximity to boundaries, and the impact on neighbours. Always check your property’s planning history too—previous alterations might affect your current rights.

Understand the limits of permitted development

Permitted development rights can be generous, but they come with strict conditions. They won’t apply in conservation areas, flats, or if your home’s already been heavily extended. If you’re exploring roof extension types, for instance, the design can’t be higher than the existing roof and mustn’t extend too far beyond the rear slope. Dormers and hip-to-gable conversions often fall within scope, but mansards typically don’t.

Prepare detailed extension plans

Once you’ve established what you’re allowed to build, it’s time to get into the details. You’ll need technical drawings that show the full scope of the work—floor plans, elevations, materials, and layout all need to be clear and accurate. For any sizeable project, especially one involving significant changes, structural calculations will be required to ensure the design is safe and compliant with building regulations.

Speak to your local planning authority

While not essential, engaging with your local planning authority before you submit can save a lot of time. They may offer pre-application advice, which gives you early feedback and helps you understand what’s likely to be approved—or rejected. Every borough interprets national guidelines a little differently, particularly in London, so knowing how your council tends to approach things gives you an advantage.

Submit your planning application

When your plans are ready, it’s time to submit. You can apply online via the Planning Portal or directly to your local council. The paperwork needs to be precise—missing documents or poorly drawn plans can cause weeks of delay. Many homeowners opt to involve professionals at this stage. Local extension builders can help you prepare a professional application, ensuring it meets the required standards and reflects practical build considerations too.

Pay the relevant application fees

Planning applications aren’t free, and the fee will depend on the type and size of extension. For a typical single dwelling extension, the cost is usually straightforward, but always check the latest figures on the Planning Portal or your council’s website. It’s worth budgeting for additional costs too, such as application drawings, consultants, and any surveys you might need along the way. Planning is rarely the cheapest part of the process, but doing it properly prevents far more expensive problems down the line.

Wait for a decision from the council

Once submitted, your application enters a formal review period. Most councils aim to respond within eight weeks, although this can stretch to thirteen if it’s more complex or if public consultation is required. A case officer will visit the site, assess the drawings, and consider the effect on neighbouring properties. If your design’s sensible and aligns with policy, you’ll likely be granted approval with a few standard conditions.

Respond to objections or feedback

Neighbours will be notified as part of the process, and they can comment or raise objections. If your application receives pushback, the council may ask for revisions. In the case of a gable end extension, for instance, concerns might be raised about overshadowing or privacy. Respond promptly and be open to compromise—minor tweaks often go a long way in resolving disputes. Keep communication polite and professional; escalating things rarely helps.

Start building once permission is granted

Once you’ve got written approval, you can move forward. The next stage is finding the right house extension builders to carry out the work. Look for experienced teams familiar with projects like yours, especially ones who understand the specifics of working in your local area. Don’t forget that planning permission isn’t the same as building control approval—you’ll still need to comply with building regulations and get sign-off at various stages of construction.