Do You Need Planning Permission for a Granny Annexe?

As families grow and living situations evolve, many homeowners are considering adding a granny annexe to their property. Whether it’s to care for aging parents, offer privacy to young adults, or create a guest space, a granny annexe can be a practical and valuable addition to any home. However, one of the most common questions is: Do you need planning permission for a granny annexe?

The short answer is — it depends. Several factors come into play, including the size, location, and intended use of the annexe. In this article, we’ll explore everything you need to know about planning permission requirements for granny annexes, helping you navigate the process with confidence.

What Is a Granny Annexe?

A granny annexe (also called a garden annexe or secondary dwelling) is a self-contained living space located within the grounds of an existing home. It typically includes:

• A bedroom or sleeping area
  
  

• A small kitchen
  
  

• A bathroom
  
  

• A living space
  
  

Granny annexes can be stand-alone structures, converted garages, or extensions to the main house. They’re designed to offer independent living facilities while still being close to the main residence.

Do You Always Need Planning Permission?

Not always, but most granny annexes do require some form of permission or legal authorization before construction begins.

Generally, you’ll need planning permission if:

• The annexe is a separate dwelling with its own front door and utilities.
  
  

• It will be occupied independently from the main house.
  
  

• You intend to rent it out or use it for purposes other than housing a family member.
  
  

• It will significantly change the appearance or footprint of your property.
  
  

However, some granny annexes can be built under Permitted Development Rights (PDR), meaning you may not need full planning permission if the structure meets certain criteria.

Let’s break this down further.

Building a Granny Annexe Under Permitted Development

Permitted Development Rights allow homeowners to make minor changes to their property without applying for formal planning permission. To qualify under PDR, your granny annexe must usually:

• Be located within the curtilage (the land immediately surrounding your house).
  
  

• Be a single-storey structure.
  
  

• Have a maximum height of:
  
  

• 4 meters if it has a dual-pitched roof
  
  

• 3 meters if it has a flat roof
  
  

• Be no taller than 2.5 meters if located within 2 meters of a boundary.
  
  

• Cover less than 50% of the land surrounding the original house (excluding the footprint of the house itself).
  
  

• Be used for purposes ancillary to the main home, not as a separate dwelling.
  
  

Important: Even if your granny annexe falls under Permitted Development, it must still comply with Building Regulations concerning safety, insulation, drainage, and more.

When Full Planning Permission Is Required

You will need full planning permission if:

• The annexe is intended as an independent home, not just an extra room or guesthouse.
  
  

• You want to rent it out to non-family members.
  
  

• The structure is significant in size or impacts the local environment (such as altering a listed building or being in a conservation area).
  
  

• You live in a designated area, such as a National Park, Area of Outstanding Natural Beauty (AONB), or Green Belt.
  
  

In these cases, you’ll need to submit a planning application to your local authority, outlining the design, purpose, and location of the proposed annexe.

Applying for a Certificate of Lawfulness

If you’re unsure whether your project falls under Permitted Development or if you simply want peace of mind, you can apply for a Certificate of Lawfulness from your local council.

This certificate legally confirms that your annexe is allowed without needing full planning permission. It can also be extremely helpful if you later decide to sell your home, as buyers will want assurance that all structures are compliant.

Key Factors Councils Consider in Applications

When reviewing planning applications for granny annexes, councils typically assess:

• Size and scale: Is it proportionate to the main house?
  
  

• Design and materials: Does it blend aesthetically with the existing property?
  
  

• Impact on neighbours: Will it block sunlight, overlook gardens, or create noise issues?
  
  

• Parking and access: Is there sufficient parking available? How will residents access the annexe?
  
  

Demonstrating that the annexe will remain ancillary (i.e., secondary) to the main house — not used for independent living — can greatly increase the chances of getting approval.

Building Regulations for Granny Annexes

Even if you don’t need planning permission, you must comply with Building Regulations. These ensure that the annexe meets safety and health standards.

Areas covered by Building Regulations include:

• Structural integrity (foundations, walls, roof)
  
  

• Insulation and energy efficiency
  
  

• Fire safety measures
  
  

• Plumbing, electrical systems, and drainage
  
  

• Ventilation and soundproofing
  
  

You will typically need inspections at various stages of the build to obtain a final completion certificate.

Common Mistakes to Avoid

When planning your granny annexe project, avoid these pitfalls:

• Assuming no permission is needed: Always check with your local council.
  
  

• Ignoring neighbours: They can object if your annexe causes disruption.
  
  

• Skipping professional advice: Architects, planners, and builders experienced with annexes can save you time and money.
  
  

• Not planning for the future: Think about accessibility features, future needs, and potential resale impacts.
  
  

Costs Involved

Besides construction costs, budget for:

• Planning application fees (if needed)
  
  

• Building regulation fees
  
  

• Architect or planning consultant fees
  
  

• Utility connections (water, gas, electricity)
  
  

On average, a basic granny annexe can cost anywhere from £50,000 to £150,000 in the UK, depending on size, specification, and design complexity.

Final Thoughts

Adding a granny annexe to your property can offer amazing benefits — from keeping family close to increasing property value. However, navigating the planning permission landscape can be tricky without proper research and preparation.

In summary:

• You might not need full planning permission if the annexe meets Permitted Development criteria.
  
  

• If in doubt, apply for a Certificate of Lawfulness.
  
  

• Always ensure your project complies with Building Regulations.
  
  

• Consult your local council and seek professional advice when needed.
  
  

By understanding the rules and planning carefully, you can create a beautiful, functional annexe that enhances your home and supports your family’s evolving needs.