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myGranny Annexe Cost
At a Glance
- Average cost to build a granny annexe is around £60,000.
- It will take approximately 7 to 8 weeks to complete.
- A garden annexe cost breakdown which includes types you can choose from.
- How long building an annexe should take.
- How to find and hire a builder using MyJobQuote.
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£60,000
Table of Contents
- How Much Does a Granny Annexe Cost to Build?
- Average Garden Annexe Cost
- Additional Costs of a Granny Annexe
- What Affects the Cost of Building a Granny Annexe?
- Labour Cost of Building a Granny Annexe
- Benefits of Building a Granny Annexe
- What's Involved in Building a Granny Annexe?
- Types of Granny Annexe
- Checklist: Hiring a Builder for a New Granny Annexe in the UK
- FAQs
How Much Does a Granny Annexe Cost to Build?
On average, the cost of creating a granny annexe is around £60,000, but prices can range from around £7,500 for a simple conversion project, all the way up to £120,000+ for a bespoke, professionally built detached annexe.
A granny annexe is a separate living space that can include a bedroom, bathroom, kitchen, and living room. As a result, it's not a cheap project. You'll need to budget for both construction and furnishings and fittings.
How much your granny annexe project will cost then depends on whether you are converting existing space, assembling a prefabricated granny annexe kit, or having a detached annexe professionally built from scratch.
Cost of Building a Granny Annexe
The average cost of constructing a new, professionally built granny annexe would typically be between £80,000 and £120,000, with these costs covering everything from laying the foundations and building the structure, to completely fitting out the interior rooms and finishes.
Cost of Granny Annexe Kits
You should be able to find self-build granny annexe kits starting at around £25,000, and they can range all the way up to £60,000+, depending on the size of your project and what's included. These kits are supplied to be assembled on site, so all foundations and utility connections will be required at an additional cost.
Cost of Converting Space into a Granny Annexe
Converting a part of your house to a granny flat or annexe is also a good option. Having a garage conversion to create a granny annexe can cost between £7,500 and £20,000. A loft conversion can cost between £37,500 and £60,000, and a basement conversion can cost between £100,000 and £160,000.
As well as which build option you choose, your granny annexe cost will vary depending on the size and complexity of the project, the level of finish you choose for the interior, and where you live, as the labour costs are a large part of the total costs, so regional variations will affect your price.
There's a big sturdy shed at the bottom of our garden and I'd love to turn it into a proper annexe for guests. What kind of costs are we talking?
"It's difficult to say without a survey, but if you allow £9,500 to £14,500 this could be a basic habitable annexe, carried out by a carpenter and joiner sole trader and the electrical work farmed out to an electrician. This is based on a log cabin effect. More specialist finishing like plastering and adding windows would increase the price."
Average Garden Annexe Cost
So, what is the typical cost of building a granny annexe?
When calculating your granny annexe costs, it's important to factor in all the costs for the entire project, from any groundworks and utility connections, to the final finish of the living space, so you know exactly how much your project is going to cost.
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Accommodation for an elderly relative
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Independent living space separate from main property
14 votes - 48%48% of votes
Private guest accommodation
3 votes - 10%10% of votes
To increase the value of your property
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Below are some examples of the typical costs associated with the construction of different types of granny annexes, although timescales will vary depending on the size and complexity of the project.
Granny Annexe Cost Examples by Build Type
| Granny Annexe Project Type | Cost | Typical Build Time |
|---|---|---|
| Build a detached granny annexe | £80,000–£120,000+ | 7 to 14 weeks |
| Granny annexe kit | £25,000–£60,000 | 2 to 6 weeks |
| Garage annexe conversion | £7,500–£20,000 | 2 to 4 weeks |
| Loft annexe conversion | £37,500–£60,000 | 6 to 10 weeks |
| Basement annexe conversion | £100,000–£160,000 | 8 to 16 weeks |
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Granny Annexe Cost Examples by Layout
As well as how it's built, the cost of your granny annexe will also depend on the size and the layout of the accommodation within it. In the table below we look at the typical costs for the different types of annexe and granny flat layouts constructed with the build options above.
| Granny Annexe Type | Conversion Project | Annexe Kit | Detached New Build |
|---|---|---|---|
| Studio Granny Annexe | £10,000–£25,000 | £25,000–£35,000 | £80,000–£90,000 |
| 1-Bedroom Granny Annexe with Bathroom & Living Area | £15,000–£35,000 | £30,000–£45,000 | £85,000–£100,000 |
| 1-Bedroom Granny Annexe with Bathroom & Kitchen | £20,000–£45,000 | £35,000–£50,000 | £90,000–£110,000 |
| Self-Contained 1-Bedroom Granny Flat | £25,000–£60,000 | £40,000–£60,000 | £100,000–£120,000 |
| Self-Contained 2-Bedroom Granny Flat | £40,000–£80,000 | £50,000–£60,000+ | £120,000–£150,000+ |
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Additional Costs of a Granny Annexe
You may discover many additional and even hidden costs associated with building a granny annexe.
If you've opted for a turnkey project, most or all of the granny annexe cost should be included in the price. Projects with prefabricated granny annexes offer a fixed price option, but additional costs such as site preparation and site survey fees need to be factored in.
Always check your quote to see what's included, but here is a rough guide to how much extra services may cost if they are not covered in your quote:
| Additional Job | Typical Cost |
|---|---|
| Professional fees | £2,000–£8,000 |
| Groundworks and site preparation | £2,000–£15,000 |
| Utility connections | £4,500–£5,000 |
| Bathroom upgrade | £4,000+ |
| Kitchen upgrade | £5,000–£10,000+ |
| Underfloor heating | £40–£190 per m² |
| Planning permission | £272–£610 |
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Professional Fees
Building your granny annexe doesn't just involve construction costs. You also need to budget for the professional fees related to design, structural engineers, site surveys, and Building Control approval. If you've opted for a turnkey build, these costs may all be included in the total price. Costs can vary considerably depending on the complexity and size of your project.
I have a nearly square area of 5 x 5 metres right up to the boundary fences, on which I am thinking of building living space, for use as office space and/or temporary living accommodation. I liken it to a studio apartment with kitchen, bathing, living, sleeping areas. Would I need planning, architectural services?
"If you plan to use the space as living accommodation, planning permission will be required, and you will also need an architect. Adding a kitchen and bathroom means drainage must be installed to connect to the sewer system."
Groundworks & Site Preparation
The costs for preparing your site for your granny annexe, which may include demolishing existing structures, levelling the ground, and groundworks to create the foundations, may all be included in your quote. As above, costs can vary massively depending on the condition of your site and how much work is required.
Utility Connections
Your granny annexe will need connecting to essential services like gas, water, electricity, and drainage. For some projects, it's relatively easy to connect to existing services without too much trouble.
But if new connections are required, or there is significant work involved in connecting utilities to your new granny annexe, costs will rise.
Bathroom Upgrades
A basic bathroom will be accounted for in your quote, with a full bathroom typically accounting for around £2,750 of your budget. However, upgrading to premium features, such as a walk-in shower or high-end tiling, could add thousands.
Kitchen Upgrades
As with the bathroom, a fully self-contained annexe or granny flat would normally include a kitchen, with new kitchen costs typically making up £2,500 to £4,000 of the total price. Upgrading the spec of your granny annexe kitchen with bespoke cabinetry or marble worktops will increase the costs significantly.
Upgraded Heating / Energy Systems
Your granny annexe quote should include the cost of installing central heating. Options like air source heat pumps, solar panels with battery storage, and underfloor heating may make your granny annexe more comfortable, but will usually cost more.
Planning Expenses
Planning permission may be required for your granny annexe. Current rates in England until 1 April 2027 are as follows (homeowners in other parts of the UK should check local rules):
- A building in the garden, separate from the house, costs £272 to apply for.
- Extending or changing the existing house to create the annexe costs £548.
- A new dwelling or one created by converting an existing building needs a full application and costs £610.
Normally, your provider would include drawings in the project's cost, and a small fee for the drawings and specifications may be charged.
What Affects the Cost of Building a Granny Annexe?
Your granny annexe quote may vary from average figures depending on factors such as:
- Annexe Location — Since the cost of hiring a builder varies by region, where you live has a significant financial impact. For example, the South East, particularly London, has higher labour rates than the rest of the UK.
- Project Timescales — The more time your labourers spend on-site, the more you will pay if labour is charged per day. The labour cost will not be impacted by the passage of time if a fixed price is settled ahead of time.
- Annexe Size — The bigger the granny annexe, the higher the price. Most of the time, it's a choice between a 1-bedroom or 2-bedroom granny annexe, but the bigger the annexe and the rooms, the more materials and time required to build it.
- Annexe Design — The shape of your granny annexe will also affect the cost of construction. Annexes in unusual shapes, for instance, are typically more expensive, and other features, such as a walkway or pergola, can also raise the cost.
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Labour Cost of Building a Granny Annexe
You will need a few different trades to build a granny annexe. Builders will be on-site for the longest, but a plumber and electrician will also be required. Per day, you can expect to pay:
| Tradesperson | Daily Rate |
|---|---|
| Builder | £200–£300 |
| Plumber | £200–£350 |
| Electrician | £250–£375 |
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Here's a quick look at what each trade will do during the build and what can impact how much their labour will cost:
- Builder — A builder will be responsible for the groundwork and building the annexe itself. The individual's level of expertise, the complexity of the project, and your location in the country will decide the exact fee you pay. Builder day rates, for example, are higher in London and the South East.
- Plumber — A plumber will be required for the water and sewer work. Sinks, toilets, and other plumbing jobs that are hard to access or need disassembly and reassembly later will take longer and cost more.
- Electrician — Lights and plug sockets will need to be installed in your granny annexe by an electrician. The number of fittings required will impact how long they need to spend on the job.
Benefits of Building a Granny Annexe
Although the initial cost of building an annexe can be high, it is often a worthwhile investment. Some of the main benefits include:
- Family can stay close, but with independence.
- An annexe may be cheaper than a care home for an elderly relative.
- It can make your property more appealing to buyers, if you decide to sell.
- Its use isn't fixed — it can be transformed into a home office, guest accommodation, or a flat for grown-up children.
- You get extra space without moving house.
What's Involved in Building a Granny Annexe?
Building a granny annexe is a large project that includes selecting an annexe, arranging utilities, and planning the site on which the annexe will be built. When you hire contractors to build your granny annexe, this is what you can expect the process to look like.
Before the Job
- Contact Contractors — First, you will contact a builder who will answer any queries you may have. A short meeting will also help improve the idea of what you're looking for and how they can assist you.
- Site Inspection — Following initial contact, your builder will come to your home for an on-site consultation. During the consultation, they will carry out a site survey to assess suitability for an annexe and walk you through the options.
- Project Requirements Outlined — Your advisor will go over the various styles of annexes available, the finishes available, and the planning permission process. In addition, budgets will be addressed so that they can better understand what you want to do.
- Project Plan Created — Following your consultation, they will create a detailed plan for your annexe and provide you with everything that's been agreed on and will guide the rest of your project.
During the Job
- Groundworks & Foundations — With all the plans and permissions for your granny annexe in place, the site is prepared for construction. This may involve demolishing existing structures, preparing the ground, and any excavation work needed to install drainage and utilities, before laying the foundations.
- Building the Structure — The structure of your granny annexe is now built, or assembled if you opted for a kit, with the roof, walls, doors, and windows all built and installed to create a weatherproof structure.
- Internal Fit-Out — With the weatherproof structure in place, all the required tradespeople can now carry out the internal fit-out to install electrics, plumbing, heating, insulation, and fit out all the rooms in the granny annexe.
After the Job
- Final Checks & Sign-Off — With work on the granny annexe complete, all the necessary final inspections and sign-off from Building Control can take place, to make sure that all the relevant regulations are complied with.
- Moving In — With all the finishing touches applied and your granny annexe ready to live in, all that's left is to move your furniture in and enjoy it.
Types of Granny Annexe
If you are unsure which type of granny annexe to get, we will go over the various granny annexes and their benefits and drawbacks. As a result, if you are undecided about a granny annexe, this section of the article will help you choose the right living space to add to your property.
Typical Granny Annexe
A traditional annexe or apartment divides a section of the house from the remainder. This section of the house will include a living area with either a kitchen or a bathroom. They may have separate entrances or share the main door, but they are always attached to the building and on the ground floor.
Ideal for large properties with extra space or gardens that can satisfy the expanded structure.
Pros
- ✔ It is located on the ground floor and is connected to your home.
Cons
- ✖ It does not have the most space.
Apartments for the Elderly
A granny flat is a variation of the traditional granny annexe. One storey of the building could be focused on becoming a flat rather than an addition attached to the home, as is common in more heavily packed city areas.
It takes up one storey of a family home, as is common in places like London, where space is limited. However, because there's not much room for an extension, this option is ideal for families who would like to stay in their own homes while embracing multi-generational living.
Pros
- ✔ It feels more like home.
- ✔ You have some independence.
Cons
- ✖ Expensive.
Ancillary Structure
This type of annexe can be built on or off-site. The idea is to create a high-quality living space in your garden.
This type of annexe should be linked to the utilities of the main house, making it auxiliary. There are multiple instances of outhouses that have been modified for elderly use.
This type can also be made from an old outhouse. So, if you're not using your outbuilding, with the appropriate utility connections and planning permission it could be converted into a garden granny annexe.
Even the humblest structures have potential, and you'd be surprised at how gorgeously even the most basic places can be transformed.
Pros
- ✔ It can be built in your garden.
- ✔ Linked to the main house utilities.
Cons
- ✖ Expensive to construct.
Prefabricated Annexes
Prefabricated granny annexes offer a simpler construction process that can also reduce costs. Again, there are numerous setups to choose from, and some companies will even let you design your annexe.
A prefabricated granny annexe is delivered with all necessary fixtures and is assembled on-site. Typically, a prefabricated granny annexe costs between £25,000 and £60,000.
Pros
- ✔ You can design it yourself.
- ✔ Then, make exactly what you require.
Cons
- ✖ It's better to build this type through a company.
Checklist: Hiring a Builder for a New Granny Annexe in the UK
Finding a builder will not be the simplest part of your project. Building a granny annexe is a complex job, so finding the right team requires careful consideration.
Once you have a shortlist of builders, it's always a good idea to ask the contractor some questions before you decide which quote to choose. Here are some questions we recommend you ask:
- Confirm experience with building annexes.
- Verify qualifications and insurance.
- Request references and examples of builds.
- Get a detailed quote covering all stages.
- Clarify timelines and payment terms.
- Ensure planning and Building Control compliance is included.
FAQs
Can a Granny Annexe Be Connected to the Main House Utilities?
Yes. Most granny annexes share the main home's electricity, water, and gas supplies. However, you may want to install separate meters so you can track the energy consumption independently. This is ideal if you are thinking of renting it out in the future.
Do I Need Building Regulations Approval for a Granny Annexe?
There are several building regulations a new annexe needs to comply with, and the cost of Building Control approval varies by local authority area. The regulations your build has to meet include Thermal Performance (Part L), Ventilation (Part F), and Fire Safety (Part B).
Can I Build a Granny Annexe Myself?
Building a granny annexe yourself can save money, but safety and precision are vital. Unless you have solid building experience, mistakes can make the structure unsafe or non-compliant.
You can handle simple tasks like decorating, but hire qualified tradespeople for construction and building regulations approval.
Do I Need to Pay Council Tax on a Granny Annexe?
In most cases, a separate council tax charge will apply to a granny annexe. In England, if the annexe is occupied by a relative of the person responsible for paying council tax on the main house, they are eligible for a 50% discount. This deduction is also applied to empty annexes or those used by the main homeowners.
A full exemption is given if the annexe is the main home of a dependent relative who is either aged 65+, substantially and permanently disabled, or severely mentally impaired. Rules vary elsewhere in the UK, so check with your local council if you live outside England.
Can I Convert an Existing Outbuilding into a Granny Annexe?
Yes, converting an existing garage, barn, or garden building is a cost-effective way to create a garden granny annexe. You will still need to make sure the structure meets Building Regulations and seek planning approval.
What Happens if I Sell My Home with a Granny Annexe?
Selling a property with an annexe can increase its value. It may, however, also attract different tax or mortgage considerations. Some buyers prefer houses with annexes for multi-generational living. Others may see it as a rental opportunity. Your estate agent can help position it appropriately on the market when selling.
