Granny Annexe Cost

By Emma
Last updated 15th May 2024 - Reading time: 24 mins
At a glance
  • The average cost to build a granny annexe is around £60,000
  • The job will take approximately 7 - 8 weeks to complete
In this article, you'll discover the following:
  • A complete pricing breakdown which includes types you can choose from, along with what such a task usually involves
  • How long the job should approximately take and a general overview of what kind of jobs can be performed
  • How to find and hire a builder

Would you like to know the costs of building a granny annexe?

In this guide, we'll go over the various costs of building a granny annexe here.

If you'd like a free quote from a builder, MyJobQuote has many builders ready to give you a free quote for a granny annexe.

To give you some idea of what to expect in terms of average costs for such work, you will need to set aside anywhere between £60,000 - £100,000.

So, if you're thinking about building a granny annexe, you'll find all the information you need right here.

granny annexe

Average Cost of a Granny Annexe:

Depending on the complexity of the job, it usually takes: 7-8 weeks


How Much Does to Build a Granny Annexe?

Multi-generational homes have become more common in recent years, either because of adult children living at home longer or because of older relatives requiring additional care.

If you've reached the point where you're concerned about the health and well-being of a loved one, you may be faced with the same decision. Building a granny annexe is the best way to keep them connected while still giving them independence.

If you would like to build a granny annexe with different contractors, you will need to budget for an architect, maintain compliance with Building Regulations, plan approval solutions, and finally, the materials and labour required to complete the project.

Many of these charges are bundled into a single entire package with prefabricated annexes. This can help save money, time, and stress.

A granny annexe is a self-contained dwelling with a bedroom, bathroom, kitchen, or living room. As a result, it's not a cheap project. You'll need to budget for both construction or furnishings and fittings. Most of the time, you can choose from a one bedroom granny annexe or a two bedroom granny annexe.

Of course, costs vary depending on the materials used, the opulence of your furnishings, the difficulty of installing any tools, how much space you have and whether you plan on converting space or constructing a granny flat from scratch.

You will have to fund the construction yourself because no granny annexe grants are available.

So, what is the cost of building a granny annexe? The average cost of constructing a granny annexe is £80,000 - £100,000 while purchasing a granny annexe kit can range between £29,000 and £51,000.

You may also have a garage conversion to create a granny annexe for £7,500 - £20,000, a loft conversion for £37,500 - £60,000, and a basement conversion for £100,000 - £160,000.

Building regulations would cost an extra £200 - £500 on top of the overall cost, and utility diversions and works would cost £4,500 - £5,000.

Granny Annex Prices

Job Cost
Cost to build a granny annexe £80,000 - £100,000
Granny annexe kit £29,000 - £51,000
Garage conversion £7,500 - £20,000
Loft conversion £37,500 - £60,000
Building regulations £200 - £500
Tool diversion or work £4,500 - £5,000
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Supply Only Costs

Saving money on labour is appealing, but the last thing you need is a dangerous and structurally unsound annexe.

granny annexe

This decision is largely based on your level of expertise and experience; however, you'll need to know what you'll need to build a granny annexe; thus, we've designed a section that only includes supply costs.

First, you will need granny annexe planning permission to ensure that building the annexe in your home or garden is safe and legal. The cost of filing a planning application varies according to where you live in the United Kingdom.

A full request for a new single home or overview planning permission in England costs £462.

To begin, you will need to ensure that your granny annexe has a sturdy base to keep it secure, so you will need to purchase pressure-treated wooden posts, which range in price from £24 to £136.

Again, you will need to know the size you require before purchasing. You will also require a shovel, which will cost between £7 and £25.

You will need premixed concrete, which will cost between £6 and £13 depending on how much you need, insulation to keep the granny annexe warm, which will cost between £19 and £49, and windows, which will cost between £129 and £400, and a door, which will cost between £40 and £600.

The plumbing on your property provides water and removes trash, contributing significantly to making your house a home. Plumbing a house from the foundation up is a difficult and expensive task. Plumbing in a new home with one master bathroom and one en-suite cost between £13,000 and £15,000.

This contains the time and effort required to construct additional plumbing throughout the property and connect it to main facilities as necessary.

A new energy supply connection typically costs between £1,600 and £2,000. However, charges may be much higher or lower depending on your specific circumstances.

Then you'll need to buy everything within your house, including decorating, furniture, a toilet, a shower, and other elements that will need to be installed after you build a granny annexe.

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Additional Costs

There is much more to building a granny annexe than you think because you are building a mini house for a family member or friend. As a result, when having one built, you may discover many additional costs associated with building a granny annexe.

As a result, we've created this section, so you'll know what extra costs to consider when building your granny annexe.

New Bathroom Cost

The size of your bathroom and the quality of the finish you desire would have a massive impact on the cost of your bathroom renovation. Of course, the bigger your bathroom, the more work will be required, but if your bathroom has an awkward layout, this will also require more work.

new bathroom

Though the fixtures themselves will consume a significant portion of your budget, the cost of labour may be the most expensive part of a new bathroom.

A small bathroom costs around £5,000, a medium bathroom costs £7,000, and a large bathroom costs £10,000 or more. A basic finish costs £2,750, while a premium finish can cost £7,000 or more.


Installing central heating is a large task that requires the installation of a boiler, new radiators, a water tank, and pipework. The average cost of installing central heating ranges between £3000 and £4000.

Everything involved is usually included in the total price quoted by your chosen central heating installer. Modern central heating systems are highly efficient and can use significantly less fuel than older systems while producing the same amount of heat.

If you would like further information, please refer to our guide on the costs of installing central heating.

New Kitchen Cost

A small kitchen will be installed in your granny annexe at an additional cost because a whole kitchen is fitted in the small home. A new kitchen's cost is divided into two parts: the kitchen itself and the installation.

Both costs can vary greatly depending on the size, complexity, and quality of the kitchen you choose to buy. Likewise, your location can significantly impact the cost of kitchen installation.

The average cost varies according to the size of your area, the type of units chosen, and the quality of equipment installed. For example, a small kitchen (approximately 3m by 3m) starts at around £2,500 and can go up to £4,000 in price. Most material and labour costs are included in this price.

Prices for a medium-sized kitchen start at around £4,000 and rise to just over £5,500. The final price will be affected by the size of your space, the quality of equipment chosen, the units, and the style is chosen material.

Labour costs will also impact the final budget required; however, this varies depending on the duration of time the installation takes, as installation methods can vary depending on the selected design.

If you would like further information, please refer to our guide on the costs of installing a new kitchen.


Of course, the cost of plastering will be measured by the amount and difficulty of the work to be done. A patch repair, for example, may cost between £70 and £130, whereas an over skim may cost between £150 and £200.

The general plastering cost also will vary depending on room size, with a small room costing £400 to £700, a medium-sized room costing £800 to £1100, and a large room costing £1200 to £1500.

The cost may also vary depending on the type of plaster you select, as some homeowners may prefer a low-cost plaster while others prefer a long-lasting premium plaster.

If you would like further information, please refer to our guide on the costs of plastering an indoor wall.

Painting a Room

Painting a room is a simple task for any painter or decorator, and it is something that any DIY enthusiast can do. Of course, the price is almost entirely determined by the size of the room.

painting home

A standard 4m by 3m room would take a couple of days to paint completely, including woodwork and coving. Outside of London, most decorators charge around £150 to £200 per day, so your total labour cost would be around £300 to £400.

Adding another £50 for the paint results in a total cost of £400.

If you would like further information, please refer to our guide on the costs of painting a bedroom.

Paint a House

In the UK, the average cost of painting a two-story, three-bedroom house is around £850. However, keep in mind that this is only an estimate, and many cost-variable factors will affect the final cost of your project.

This includes the size of your home, its design, the materials used, and the tradesperson's hourly and daily rates.

When you hire a professional painter or decorator to paint the exterior of your home, you usually pay for all materials, supplies, and labour. In most cases, you will need to erect scaffolding before having the exterior of your home painted.

If you would like further information, please refer to our guide on the costs of painting the exterior of a house.

Labour Costs and Timescales

You will almost certainly need the services of a builder for construction projects or structural work. We'll go over the labour costs for constructing a granny annexe without any supplies or extra fees.

building a granny annexe

You should budget between £150 and £280 a day for a tradesperson to build your granny annexe. The exact fee you pay will be decided by the individual's level of expertise, the complexity of the project, and your location in the country. Builder day rates, for example, are larger in London and the Southeast.

A self-employed person can expect to earn around £25 per hour. Working as a self-employed differs from working for a construction company in that self-employed individuals typically charge a lower hourly rate because they do not have to cover a larger firm's institutional and overhead costs. This will, however, vary depending on your experience and location in the United Kingdom.

As with all professionals, getting at least three quotes from different builders in your area is recommended. You should shop around to make sure you're paying a fair and competitive cost for the project.

Depending on how large, complex, and/or finicky the plumbing project is, you may need to hire a plumber 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.

Most plumbers cost between £20 and £40 per hour, but the total cost depends on the context of the job.

Lights and plug sockets will need to be installed around your granny annexe by an electrician. You should expect to pay between £280 and £450 for this service. However, we've received quotes as low as £150 per day for other jobs. So consider paying around £75 per hour for an electrician in London.

Moving on to the time required to construct a granny annexe. The decision to build an annexe is arguably the most difficult because it usually necessitates many members of your family to make a decision on how it will all function together.

The process is not one to rush into with financial considerations such as income tax, granny annexe council tax, operational costs, moving fees, and more.

When you've decided on a company to build your annexe with, you'll usually pay a deposit before proceeding to the next stage, which is the critical Planning Permission stage. This takes about ten weeks on average.

The following steps are the foundations and main service connections for your annexe. This process usually takes 1-2 weeks, based on where your home is located, the quantity of ground equipment needed, and the overall size of your annexe.

The average onsite build takes 7-14 weeks to finish, depending on the size and requirements of the annexe, from the installation of the frames, windows and doors, roof and cladding outside to the installation of the bathroom and kitchen, flooring, plumbing, electrical work, painting, and décor inside.

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Cost Factors of Building a Granny Annexe?

There are numerous cost factors to consider when building a granny annexe, and we will go over the various cost factors that may affect the overall cost of your granny annexe.



Since the cost of hiring a builder varies by region, where you live has a significant financial impact. For example, the southeast, particularly London, has higher labour rates than the rest of the UK.


Because of labour costs, the more time you spend onsite, the more you will pay if labour is taxed per day. If the work took two days and three hours or six days, you would be charged three days of labour. The labour cost will not be impacted by the passage of time if a fixed price is settled ahead of time.


The bigger the granny annexe, the higher the price when it comes to size. This is entirely normal. The bigger the room, the more materials and time required to build it. As a result, the granny annexe will be more expensive.

There are some additional expenses to consider. Many people fail to realise that building a larger granny annexe necessitates more use of screws, nails, and other equipment.


The shape of your granny annexe will also affect the cost of construction. Garden rooms in unusual shapes, for instance, are typically more expensive. Other features, such as a walkway or pergola, can raise the cost of a garden room.

Planning Expenses

If you need Planning Permission to build your granny annexe, you will have to pay a processing fee of around £170. Normally, your provider would include drawings in the project's cost, and a small fee for the drawings and specifications may be charged. However, if Building Control consent is granted, there may be extra fees to pay.

What's Involved in Installing 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. This section will go over the processes required to install a granny annexe.

Step 1

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.

Step 2

Following initial contact, your builder will come to your home for an onsite consultation. During the consultation, they will evaluate your garden and its suitability for an annexe and walk you through the options.

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.

Step 3

Following your consultation, they will create a detailed plan for your annexe and provide you with everything that you need to decide as well as proceed, including:

  • The procedure for obtaining planning approval
  • Warranty and construction guarantee
  • Project timelines and expectations
  • The annexed construction specifications
  • Your annexe's complete footprint and elevation designs
  • The fees for the building permit application
  • A comprehensive cost breakdown
  • Any additional costs for the additional effort
  • The construction payment schedules

Step 4

As soon as contracts are signed, they begin applying for planning permission. The action from your Planning Authority will take between 8 and 13 weeks on average.

Step 5

You should have a point of contact throughout the process and ensure that you are always kept up to date. If you have any questions, you should contact your project manager.

Step 6

Seeing your annexe become a reality is the most exciting part. The tradespeople will be working in your garden, finishing groundwork, and arranging utility connections; your new annexe will be supplied and assembled once finished. After the finishing touches are applied, you will be able to move into your new home!

Can I Build a Granny Annexe Myself?

The idea of saving money on labour is appealing, but the last thing you need is an unsafe and structurally unsound annexe. Of course, this decision depends entirely on your skill and experience level, but please keep in mind that measurements must always be exact, or you will end up with an annexe that does not fit properly.

If you want to create a DIY granny annexe, a self-build granny annexe is usually the best option.


Working with electricity or gas without professional help is never a good idea. It's worth considering a prefabricated annexe.

If the job is not done safely, you risk injuring or damaging your family or home. Building a granny annexe is a difficult task that requires various skills.

You might be able to save some money by doing simpler tasks like decorating yourself. However, building an annexe takes time and effort. Building codes must always be followed. Hiring a qualified tradesperson will ensure that this is always done.

Please keep in mind that the average cost of obtaining building regulations approval is £200. We would highly advise hiring a professional due to the project's complexity and difficulty.

Building Regulations & Planning Permission for a Granny Annexe

Getting a Granny Annexe Planning permission for your new granny annexe will undoubtedly cause you to experience a range of emotions as you consider if building an annexe in the backyard is the best option for you and your family.

The daunting prospect of obtaining approval to build a granny annexe in your backyard from your Local Planning Authority arises early in the decision-making process when building a granny annexe (LPA).

A granny annexe with a person living in it will always require planning approval or a Certificate of Lawfulness from your LPA.

Some temporary structures, including leisure structures that will not be occupied, may not require planning permission. This isn't something you should try on your own. It should only be handled by experts in obtaining residential planning permission in the United Kingdom.

The simplest way to determine your chances of obtaining planning approval for your granny annexe is to schedule a free onsite consultation with an expert.

For instance, you may want a pitched roof annexe, but they may advise you during our free onsite consultation that a flat roof annexe is your best option because several neighbours overlook the house.

You may have also heard that the Caravan Act is a "silver bullet," but it will necessitate a License of Lawfulness from your Planning Authority. When you obtain planning permission to construct an annexe in your back garden, you collaborate with your planning authority to develop the land.

They will have a say in how it looks, what components and finishes are used on the exterior, and which size and style they will accept.

The Caravan Act allows you to apply to site a temporary structure on the land rather than develop it.

We recommend the normal Householder's Planning Application route for Granny Annexes that are considered "straightforward" during onsite consultation. This is the same type of planning approval you would apply for if you had been building an extension or attaching something to your garden, including a raised decked area.

Some Local Planning Authorities will request a Full Application if they consider a Granny Annexe a new dwelling. However, even within the same county, there appears to be very little consistency in this regard across Local Planning Authorities.

Your local planning authority is likely to be concerned about things like:

  • The overall size of the Granny Annexe compared to the main house and the size of your garden.
  • The living accommodation must be specified as ancillary to the main house to be considered an annexe.
  • They will want to know why you want to construct a granny annexe in the garden, who will live there soon, and what long-term plans you have for it.
  • Planning permission will only be granted if you meet all the necessities of your Local Planning Authority, including the concerns raised by the Local Planning Office in charge of your application.
  • Our planning specialists will prepare all the necessary drawings, applications, and design or access statements on your behalf.
  • When handling your planning application, all Local Planning Authorities adhere to the same timescales and will often decide within 8 weeks of validating your submitted planning application.

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 assist you in making your decision.

Typical Granny Annexe

A traditional Granny Annexe divides a section of the house from the remainder. This section of the house will include a living area with either a kitchen or 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.


  • ✔ It is located on the ground floor and is connected to your home


  • ✖ 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 current homes.


  • ✔ It feels more like home
  • ✔ You have some independence


  • ✖ Expensive

Ancillary Structure

This type of annexe can be built on or off-site. The idea is to build a semi-permanent or permanent mobile home in your backyard.

The structure 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, it could be converted into a granny annexe.

Even the humblest structures have potential, and you'd be surprised at how gorgeously even the most basic places can be transformed.


  • ✔ It can be built in your garden
  • ✔ Linked to the main house utilities


  • ✖ Expensive to construct

Prefabricated Annexes

An annexe can also be bought prefabricated. Again, there are numerous setups to choose from, as well as some companies will even let you design your annexe.

building granny annexe

A prefabricated annexe is delivered with all necessary fixtures and is assembled onsite. Typically, a prefabricated granny annexe prices both £40,000 and £40,500.


  • ✔ You can design it yourself
  • ✔ Then, make exactly what you require


  • ✖ It is better to build this type through a company

Hiring Contractors to Build a Granny Annexe Checklist

Finding a builder will not be the simplest part of your project. Indeed, with a trade shortage resulting in a 20-year high in demand for construction work, finding the right team to take on your project is more difficult than ever.

However, the significance of bringing in the right builder cannot be overstated. It will not only result in the highest quality build but having a good connection with your builder will make sure you get what you want while possibly saving you time and money.

Finding a local builder can have significant advantages for your construction. Time on site, understanding of local planning permission, builders' merchants, and other local trades are all important resources that you'll appreciate.

If you've previously used an electrician or a local plumber and were pleased with their work, contact them and request if they have any recommendations for good builders. Most tradesmen become accustomed to seeing the same names on the job sites and frequently have preferences for who they prefer to work with.

Once you've found a builder you like, meeting former clients is a great way to learn about the value of a builder's work and other important factors.


How big can a granny annexe be?

The eaves cannot be higher than 2.5m. If the building is within 2m of a boundary, no part can be taller than 2.5m.

New outbuildings for houses in designated areas must be located behind the rear wall but not on areas belonging to the side elevations. You should consider all of these when creating the granny annexe floor plans.

Is it worth building a granny annexe?

Including an annexe in your home design could also be financially beneficial. Adding an annexe will increase your home's value, but you can also rent it out to generate a profitable secondary income.

Do you need planning permission for a granny annexe?

A granny annexe with occupants will always require planning permission or even a Certificate of Lawfulness from your LPA. However, some temporary structures, such as leisure buildings that will not be occupied, may not require planning permission.

How much space do you need for a granny annexe?

When attached to the main building, an annexe requires at least 50cm of space between the boundary and the building, while an extension can be built nearer to the boundary.

How to know if a builder is reliable?

A trustworthy builder will be eager to present you with examples of their prior projects and provide feedback from previous customers. Request to see their finished work and speak with their clients. If they refuse, you must wonder why.


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