Understanding Annexe Planning Permission

An annexe—sometimes referred to as a granny flat—is a secondary living space within the grounds of a primary residence. They can take many forms, from garage conversions and garden studios to purpose-built extensions. Annexes offer additional accommodation while retaining a degree of independence from the main house.

Traditionally, annexes have provided secure and flexible housing for elderly relatives. However, with rising property prices, many families are now creating annexes to support younger family members.

Whether you are looking to convert part of your home or build a stand-alone annexe in your garden, understanding the planning rules is essential to avoid costly mistakes.

Do I Need Planning Permission for an Annexe?

As is often the case in planning, the answer depends on the specific circumstances of the case. The main consideration is the type of development and its relationship to the main dwelling.

• Conversions within the existing house
  In many cases, converting part of your existing property to form an annexe does not require planning permission, provided the space remains ancillary to the main dwelling. This usually means it is used by members of the household, shares services such as water and electricity, and maintains a functional link with the primary residence.

• Extensions under Permitted Development
  If you plan to extend your property to create an annexe, planning permission may not be necessary if the extension falls within Permitted Development Rights.

• However, in either of the above cases, we strongly recommend applying for a Lawful Development Certificate from your council. This provides written confirmation that the works are lawful, helping you avoid costly mistakes or future enforcement action.

• Standalone annexes in the garden
  A separate, self-contained annexe in your garden will require planning permission. Even if it would otherwise comply with Class E Permitted Development criteria, using a garden building as sleeping accommodation is explicitly excluded from these rights.

Key Factors Local Authorities Consider

When determining planning applications for annexes, Councils assess a range of factors. Understanding these can significantly improve your chances of approval.

Local Plan Policies

Every council has its own set of planning policies contained within their Local Plan. Some authorities specifically encourage annexes, and others seek to only permit annexes that are physically attached to the main property. At Cedar Planning, we review the Local Plan and advise on the best strategy for your proposal.

Size and Design

The impact of the proposed annexe on the surrounding area is another pivotal consideration. Councils will assess whether the annexe is proportionate to the main house and whether its design is in keeping with the character of the area. High-quality materials and sympathetic design are particularly important in Conservation Areas, the countryside, or National Landscapes.

Functional Use

An annexe should always remain functionally linked to the host dwelling. Councils often impose conditions restricting use to close family members and preventing the unit from being let or sold separately. Legal agreements can often be sought in such cases.

Residential Amenity

Like all home extensions, annexes must respect the amenity of neighbours. Careful siting and window placement can avoid issues of overlooking or overshadowing.

Can I Rent Out My Annexe?

Using an annexe as a holiday let or rental property for non-family members is treated differently in planning terms. This use would usually be considered a new planning unit, requiring a change of use application.

In some cases, if an annexe has already been used as a holiday let or rental for a continuous period (typically 4 or 10 years, depending on circumstances), you may be eligible to apply for a Certificate of Lawfulness to confirm its use is now lawful. Success depends heavily on the strength of your supporting evidence, and Cedar Planning are well-placed to help with this.

How We Can Help

Planning for an annexe can be complex, with rules varying between councils and depending on how the space will be used. At Cedar Planning, our experienced consultants can:

• Review your proposal against local and national planning policies

• Advise on whether planning permission is required

• Prepare and submit applications, including Certificates of Lawfulness

• Negotiate with local councils to give your project the best chance of success

If you’re considering an annexe for your property, contact Cedar Planning today and let our experts guide you through the process with confidence.