Buying a Home with an annexe in mind

It’s not surprising that the popularity of building annexes continues to increase and NAPC receives many enquiries from home buyers wanting to buy a property, but if only an annexe could be approved in the garden.

This could be due to moving elderly parents in with them to allow additional care or children to be allowed to save towards a mortgage.

Planning to move can be stressful and daunting, especially with the cost of living rapidly increasing at a scary rate. Putting so much faith in gaining planning permission for an annexe can also contribute to this anxiety.

Although we cannot 100% guarantee every planning application to be approved, we can draw upon our many years of experience and knowledge to appraise your chances of success

We have outlined aspects to consider when buying a home with an annexe in mind.

1. Location

Certain areas will add another level of complexity when it comes to the planning process so it may be worth researching your area in advance.

What are these areas?

These could be if the home is situated within a Green Belt, Area of Outstanding Natural Beauty, or Conservation Area. Although we have successfully gained approvals within these, the process of approval may take longer or be refused altogether.

Extra attention to the size and design of your annexe will need to be considered to ensure the building fits into the character of the environment surrounding it.

Additionally, Listed buildings may face similar complications, however, working with a planning expert will give you the best chance of success. NAPC has recently received approval for a 37.5 sqm annexe within the grounds of Grade II Listed Building. To read this blog please follow this link


We recommended researching the annexe you would like from a variety of providers or builders within the area. For instance, two-bedroom garden homes will have a greater footprint and therefore greater construction costs.


Also, keep in mind the costs of submitting a planning application. You would require proposed elevation and floor plans at a scale of 1:100, a proposed block plan showing the location of the garden room at a scale of 1:500, and a location plan at a scale of 1:1250 to progress with the planning application as a minimum.


You will have to consider application costs to your Local Planning Authority, planning consultancy costs, and the annexe provider within your budget, plus your costs of moving into a new home.


Yes, an annexe in the long term will increase the value of your property down the line but you must be aware of all aspects before committing. On average, it’s estimated that it will cost between £70,000 – £140,000 to build a standard-sized annexe in the UK; dependent on various factors.


When considering the suitability of a property for an annexe, it is always worth ensuring that there is only one access to the site.

To ensure the annexe cannot be independently accessed it should share the same access as the dwelling and not have its own, for instance, rear garden access.

This will help reinforce the ancillary argument and function link with the host dwelling.

4. Design

When looking at the aesthetic of the granny annexe, it is important to integrate the annexes’ appearance with the surroundings. Aspects such as exterior cladding, roof tiles, and fenestration could reflect this.

It is also worth considering the materials you would like to use as this will mean the costs will vary.


Most councils, in our experience, favour annexes of a smaller scale and will question the need for a larger one. NAPC will estimate the sqm likely to be approved for your proposed annexe by looking at your current garden space, ideal location, and previously approved cases.

As an example, these are the average size approved by a number of Local Planning Authorities

East Devon District Council – 65sqm

Bristol City Council – 44 sqm

Bath and North East Somerset Council – 58qm

Bassetlaw – 83sqm

Mid Sussex District Council – 48sqm

As shown, the average varies from place to place.

So, it is a good idea to ensure that any garden is big enough to accommodate an annexe. A good rule of thumb is that an annexe should take up no more than 50% of the garden.


NAPC – Planning Consultants

Get in touch with NAPC to talk through any potential projects you may have, we are happy to help and guide you on whether a property is suitable for an annexe in the garden.



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Get an answer quicker with a Feasibility Study

A one-off Feasibility Study (from £99) will equip you with crucial planning insight about the area you’re planning to site your Annexe or Garden Room. So if you pursue your application, you have the best chance of success. 

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