a typical back garden where a granny annexe would fit

How Big Can A Granny Annexe Be?

How big can you make your annexe? Is your garden big enough? How big will planning permission allow you to go? These are all common questions at the start of your granny annexe journey.

In this blog, we aim to answer any size and planning related queries you may have!

How Big Can You Go?

When you are considering installing a granny annexe in your garden, there are a few simple tests you can perform to check that you have enough space and that your project will comply with Local Planning Authority (LPA) rules.

Although LPA rules vary across the country, when looking at planning permission for your annexe, one key factor they will consider is the size of your proposed annexe in relation to your existing home and the land or garden which surrounds it.

Hawthorn Granny Annexe Dimensions

In addition to being considered ancillary or subordinate to your property, an annexe must not have a footprint bigger than your main home.  

Also, your LPA will look at the combined footprint of your home, the proposed annexe and any other outbuildings or extension. The more of your overall property (land) taken up, the tricker it becomes for planning permission to be granted.

So, if you’re trying to work out how big your annexe can be, it is best to stay on the conservative side before working out sizes and choosing a granny annexe.

How To Check You Have Room For An Annexe

To work out how big your granny annexe can be, it is easier to have some measurements in mind already. With many annexe providers offering pre-fabricated annexes at standard set sizes, make a shortlist of the ones you think will be big enough for your needs – bare in mind if it turns out you have plenty of room you can go back and choose a bigger annexe, or a smaller one.

Most annexes come in one or two-bed versions so establish the simple things like how many bedrooms you would like. To enable you to easily put together a shortlist, our annexes all have their measurements displayed, as well as prices for budgeting purposes.

This might all sound a bit complicated but there is a super simple way to check how big your annexe can be and therefore, the likelihood of being granted planning permission.

  1. Find out the footprint of your existing house and your garden – you can usually find this on your title deeds or just measure it yourself.
  • Using a piece of graph paper, plot out your house and your garden.
  • Add on any existing extensions or outbuildings.
  • Add to the plan, one of your shortlisted annexes.

With your home, garden and annexe plotted out, it should now be easy to see how much land is left. Anything less than 50% of the overall size and you will struggle to get permission for the annexe.

If your first choice of annexe is too big, choose a smaller one or if you have plenty of room and want to see how big you can go, add on a lager annexe.

Be sure to use a pencil so you can erase and change your annexe size!

Granny Annexe Planning Permission

If you are not confident with your measurements or are still confused about the size your annexe can be, then don’t worry – if you’re looking at choosing one of our annexes, we include a site survey and planning permission service as part of your overall package.

Checking how big you can go is a good idea to give you a realistic idea of what sort of annexe we will be able to provide but once you have been in touch with us and had your initial consultation, one of our annexe experts takes over and you don’t need to worry about a thing.

Granny annexe planning permission and size-related queries can often be a homeowner’s biggest concern when choosing an annexe, that is on top of family care worries and budgeting. That is why we provide these services to help make your families journey to a shiny new annexe as smooth as possible!

Please get in touch if you have any questions about our annexes or planning permission – a friendly, knowledgeable member of the team will be happy to assist you.

Hawthorn Granny Annexe with Tiled Roof

Are There Any Additional Costs When Building A Granny Annexe?

Multi-generational homes have become increasingly popular in recent years – either through adult children staying at home for longer or older relatives needing a bit of extra care.

One of the most popular solutions for such families is a prefabricated granny annexe. It can also be one of the most cost-effective options when you choose the right provider or builder.

Here are some average project costs and an explanation of any additional costs you may run into when building your granny annexe.

What Is The Cost Of Building A Granny Annexe?

If you set out to build your annexe, using separate contractors, there are many different costs to factor in, which may include; an architect, checking you are compliant with Building Regulations, planning permission services, and then the materials and labour required to build.

The beauty of prefabricated annexes, especially when you use a turnkey service like ours, is many of these costs are included in one overall package. This can save you money, and of course time and stress.

Prices for prefabricated annexes will also vary between providers but you can expect to pay upwards of £40,000.

Our high-quality annexes start at just £55,250 and go up to £105,250 for our largest two-bed model.

Bluebell Granny Annexe Living Area

Will There be Any Additional Granny Annexe Costs?

As mentioned, the beauty of using an annexe builder is all your granny annexe costs will usually be wrapped up in on package meaning you can budget effectively and there won’t be any surprises.

Our turnkey service includes building plans, a site survey, planning permission service, and installation. Connection to utilities such as electricity and water are also included.  

This means once we have agreed what you want and hand over your plans and a quote, the price you see is the total cost for everything.

There are significant advantages to building your annexe this way; it’s often more cost-effective than sourcing separate contractors for each portion of your project, plus the process is more efficient and stress-free. Once you have signed your contract, you simply sit back and wait for your finished annexe.

Some families appreciate this hassle-free approach, especially when the need for an annexe is urgent. For example, if an older family member has become poorly and accommodation is needed sooner rather than later.

There are a few circumstances where you may incur additional costs with one of our packages, but most of them are voluntary.

For example, our annexes come with a standard specification, but you can upgrade any element of the design depending on your needs and budget. Step-in showers can be upgraded to wet rooms, a pitched rather than a flat roof can be added, and we can customise details such as cupboard doors and flooring. This will all be thoroughly discussed with you before we finalise your quote.

Groundworks are included in your package but there are some circumstances where additional works may be needed, and these can cost extra. Additional groundworks are sometimes required for a utility connection (water, for example) when your annexe is situated further away from your main property than is standard. This isn’t common in your average back garden though and would be picked up during our site survey.

Non-Build Costs To Bear In Mind

In addition to annexe building costs, there is some ongoing cost to bear in mind that are worth mentioning here.

Granny annexes are subject to separate council tax bills – if the annexe is used by the main house owner or a family member, this fee is reduced by 50%. However, the bill can be completely written off if your family member is classed as a ‘dependant’ (example include someone over the age of 65 or a family member with a substantial/permanent disability)

Annexe maintenance costs are minimal as our annexes are designed to be ‘weatherproof’ and last a long time, but you will need to factor in running costs for your annexe. This includes electricity, water, and internet/telephone bills. Most families have one bill for these utilities and then split accordingly but it is something you should discuss as a family before proceeding with your project.

Family Annexe

We hope this rundown of the basic prices and any additional costs has given you a better idea on the overall cost of building a granny annexe.

If you would like to ask us any questions about our annexes or prices, please give one of our friendly advisors a call on 0330 1332 668 or get in touch here.

Sycamore Granny Annexe Living Area

Granny Annexe FAQs

If you’re considering a granny annexe for you or a loved one, it can be hard to know where to start. Elderly care tends to be the driving factor behind most annexe projects, and the whole family needs to agree prior to making such a commitment. 

So, with this being one of the most significant purchases you’re likely to make, please read our list of quick-fire granny annexe FAQs to learn more about garden living, and help you make the right decision for you and your family.

Granny Annexe FAQs: Planning Permission

Will I need to obtain planning permission for one of your annexes?

If a building is used for habitation with all the main services, a kitchen, bathroom and bedroom, then yes. This can be done with either householder applications or the ‘Caravan Act’. Either one requires approval from your Local Planning Authority (LPA), which we can obtain on your behalf.

What’s the difference between planning permission and the ‘Caravan Act’?

Planning permission is development of land, whilst the Caravan Act relates to the use of land. Both are decided by your local LPA.

Do you guarantee planning permission?

No, nobody can guarantee that, and it really depends on the merit of each application. Our planning consultant specialises in annexe applications and has over a 90% success rate in both England and Wales.

Do annexes need to adhere to Building Regulations?

Most annexes are built as ‘mobile homes’, and as such, they don’t fall under Building Regulations. That said, at Family Annexe we ensure that all of our annexes are put through Building regulations for added peace of mind.

How long does it take to obtain permission to build?

In our experience, it typically takes around 12-weeks to obtain permission via a householder application or via the Caravan Act. Every planning application has to be dealt with within 8 weeks of your planning application being verified by your LPA (a process, which can take up to 4-weeks itself). When LPAs are busy, time extensions can often be requested.

I live in a listed building. Can I have a garden annexe?

Yes you can. Some external materials may have to be adapted to pacify your conservation officer (i.e. adapting Thermowood cladding to untreated oak), but many annexes have been built in the gardens of listed properties.

My garden is in a conservation area. Can I have an annexe?

Yes, it’s quite possible. Our team have plenty of experience when it comes to planning, and we can usually find the perfect solution that provides you look you desire whilst adhering to local conservation guidelines.

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Granny Annexe FAQs: Finances

How much does an annexe cost?

Our pricing is extremely transparent. Everything is included within the price barring wetroom upgrade (£1,000), pitched roof upgrade (priced per model), or any anomalies re. groundworks — i.e. new septic tank. The Bluebell is our entry-level one-bedroom annexe, which costs £55,250. This price includes everything detailed within our specification, as well our fully-managed planning service. Our two-bedroom annexes start from £89,250.

What are your payment terms?

We take a £2,000 non-refundable payment for our planning service when you initially place your order. This fee is deducted from the overall cost of your annexe, and we then split the remaining balance into four equal payments.
The first is due once we obtain planning permission and book your build slot.
The second is due on week two of your build — once groundworks are complete and your annexe ‘kit’ arrives. The third payment is due once all internal walls have been plastered. And the final payment is due just before we hand over the keys, subject to your approval.

Can I sell my annexe as a separate dwelling in future?

No, we’re afraid not. Planning permission will state that the annexe must remain ancillary to the main house and can never be sold separately.

Will I pay council tax on my garden annexe?

Probably not. Annexes are exempt from council tax as long as it forms part of the main home and the person living in it is a dependent relative.

Will an annexe add value to my property?

Yes, without question. A garden annexe adds value to a property by providing at least one extra bedroom and bathroom. “House with annexe” is a growing trend online with estate agents, as potential buyers can turn it into a holiday let or spread their own family out.

Are your annexes cost-efficient to run?

Yes, they’re comparable with a small new build home. The timber structure is super-insulated and PVCu windows are A-rated. Where possible, we install gas central heating as part of the price. When gas isn’t as option, we install digital electric radiators, which when properly calibrated, are extremely efficient. Water, gas and/or electric are all fed from the main dwelling.

Granny Annexe FAQs: Specification

Can I have a kitchen?

Yes you can. We supply a choice of kitchen cabinets, handles and worktops from Howdens, and you can pick from a range of colours.

Do you provide bathroom fixtures and fittings?

Yes, each annexe comes with a fully-fitted shower room and additional ensuite facilities in our larger two bedroom annexes.

Can I have a wetroom?

Yes, we can install a wet room instead of shower room for an extra £1,000.

Does it cost extra to connect my annexe to services?

No. We include a standard 10m service run for all annexes within the price.

Are all electrics and heating included within the price?

Yes. Gas central heating or digital electric radiators are fitted as standard.
We also install all electric sockets, switches and LED downlights throughout.

How long will my annexe last?

There’s no reason why one of our annexes won’t last at least 70-years.

What cladding do you use on the outside?

Thermowood is our standard finish, which is a beautiful heat-treated timber that’s both sustainable and chemical-free. Other popular options available for the same price are Marley Cedral Lap weatherboard or green untreated oak for a more natural finish (a popular choice in conservation areas).

Don’t flat roofs leak?

Not at all. EPDM synthetic roofs have significantly advanced over the past few years, and all our flat roofs come with a manufacturers warranty.

Can you build a pitched roof?

We certainly can. For a small upgrade, each of our annexes can be finished with a warm pitched roof, available with a choice of roof tile. Ceilings are vaulted in main living/dining areas to create an additional sense of space.

What are your annexes built on?

We typically use a concrete pad system. But we can also use a ‘Swift Plinth’ foundation system to minimise disruption if tree large roots are nearby.

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