Do I Need Planning Permission? A Guide for Cornwall Homeowners

One of the most common questions we hear from homeowners is "Do I need planning permission?" The answer depends on what you're planning to build, where your property is located, and whether your home has had previous extensions or alterations.

What is Permitted Development?

Permitted Development (PD) rights allow homeowners to carry out certain types of building work without needing to apply for planning permission. These rights are set by the government and apply to most houses — though there are important exceptions.

Even when work falls within permitted development, you may still need to apply for Building Regulations approval — these are separate requirements that cover structural safety, fire safety, insulation and other technical standards.

When You Usually DON'T Need Planning Permission

Single Storey Rear Extensions

For detached houses, you can usually extend up to 8 metres from the rear wall (or 6 metres for semi-detached and terraced houses) without planning permission, provided the extension is single storey and meets certain conditions regarding height and proximity to boundaries.

Loft Conversions

Most loft conversions, including dormer windows to the rear of the property, fall within permitted development. You can typically add up to 40 cubic metres of space to a terraced house, or 50 cubic metres to a detached or semi-detached house. However, dormers facing a highway usually require permission.

Garage Conversions

Converting an integral or attached garage to living space is generally permitted development, as you're not adding floor space — you're simply changing the use of existing space. The main consideration is the design of the new front wall where the garage door was.

Outbuildings

Garden rooms, workshops and home offices can often be built under permitted development, provided they're single storey, under 2.5m high if within 2 metres of a boundary, and occupy no more than 50% of the garden area.

When You WILL Need Planning Permission

Special Considerations in Cornwall

Cornwall has some unique planning considerations that don't apply in other parts of England:

Cornwall AONB

Around a third of Cornwall is designated as an Area of Outstanding Natural Beauty. In these areas, permitted development rights for extensions are reduced — for example, the larger rear extension allowances (8m/6m) don't apply in the AONB.

Barn Conversions — Class Q

Agricultural buildings can sometimes be converted to residential use under Class Q permitted development rights. This allows conversion without full planning permission, though you need to apply for "prior approval" from Cornwall Council, who will assess factors like flooding, highways and contamination.

Class Q has specific requirements — the building must have been in agricultural use on a certain date, structural works must be minimal, and there are limits on the floor space that can be converted.

Coastal and Flood Risk Areas

Properties in flood risk areas or near the coast may face additional scrutiny. Even if your proposal is permitted development, you should check whether there are flooding or coastal erosion concerns that could affect your plans.

How to Check If You Need Permission

There are several ways to establish whether your project needs planning permission:

• Lawful Development Certificate: Apply to Cornwall Council for a certificate confirming your work is permitted development. This provides legal certainty and is useful when selling your property.
• Pre-application advice: Cornwall Council offers a pre-application service where you can get guidance on whether permission is needed and what might be approved.
• Planning Portal: The government's Planning Portal has interactive guides to help you understand permitted development rights for common projects.
• Professional advice: An experienced builder or architect can assess your property and proposals, taking into account its specific circumstances.

What Happens If You Build Without Permission?

Building without required planning permission is a serious matter. Cornwall Council can take enforcement action requiring you to alter or remove the unauthorised work. This can be extremely costly and disruptive.

Even if no action is taken immediately, problems often arise when you try to sell the property. Solicitors will ask for planning documentation, and if you can't provide it, sales can fall through or you may need expensive indemnity insurance.

Our Advice

If you're in any doubt about whether your project needs planning permission, it's always worth checking before you start. The small investment in getting proper advice upfront can save significant problems later.

At VR Building Contractors, we regularly advise clients on the planning status of their projects. We can help you understand what's achievable, prepare any necessary applications, and ensure your project proceeds smoothly through both planning and building regulations.