Granny Annexe Cost

How Much to Build a Granny Annexe?

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.

Average Granny 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.

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 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.

Additional Granny Annexe 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 and even hidden costs associated with building a granny annexe.

What is your main reason for building a granny annexe?

Accommodation for an elderly relative

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Independent living space separate from main property

5 votes - 42%42% of votes

Private guest accommodation

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To increase the value of your property

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If you've opted for a turnkey project, most if not 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.

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

Planning & Professional Fees

Building your granny annexe doesn't just involve construction costs, you also need to budget for the professional fees related to planning, 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. However, depending on the complexity and size of your project, if these are not included in your quote you could expect to pay an additional £2,000 to £8,000.

Groundworks & Site Preparation

Again, the costs for preparing your site for your granny annexe, which may include demolishing existing structures, levelling the ground, and groundworks to create the foundation, may all be included in your quote.

If these aren't included, depending on the condition of your site and how much work is required, site preparation and groundworks could add between £2,000 and £15,000 to your granny annexe project.

Utility Connections

Your granny annexe will need connecting to essential services like water, electricity, drainage, and possibly gas. 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, you could expect additional costs of between £4,500 and £5,000.

Bathroom Upgrades

The bathroom is probably one of the most essential features of any granny annexe if you want truly independent living, with a full bathroom typically costing around £2,750 for a basic finish.

You could look at upgrading your bathroom and giving it a higher spec, although this will be more expensive. The price for giving your granny flat bathroom a premium finish could be as much as £7,000 or more, significantly adding to your project costs.

Kitchen Upgrades

A fully self-contained annexe or granny flat would normally include a kitchen, with new kitchen costs typically around £2,500 to £4,000.

However, if you decide you want to upgrade the spec of your granny annexe kitchen this could start to get expensive, with bespoke cabinetry, marble worktops, kitchen islands, and high-end appliances potentially adding thousands of pounds to your project costs.

Upgraded Heating / Energy Systems

Your granny annexe should include a standard heating system, with costs for installing central heating ranging from £3,000 to £4,000. However, you might decide you want to upgrade your heating and energy systems for something more energy efficient.

While options like air source heat pumps, solar panels with battery storage, and underfloor heating may make your granny annexe more comfortable, these could add several thousand pounds to the cost of your project, but could pay off in the long run.

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Factors That Impact Granny Annexe Building Costs

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.

Annexe Location

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.

Project Timescales

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.

Annexe Size

The bigger the granny annexe, the higher the price when it comes to size. Most of the time, it's a choice between a one-bedroom granny annexe or a two-bedroom granny annexe, but the bigger the annexe and the rooms, 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.

Annexe Design

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 £548. Normally, your provider would include drawings in the project's cost, and a small fee for the drawings and specifications may be charged. However, most granny annexes will also require Building Control approval, which will mean additional fees to pay.

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.

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Labour Cost of Building a Granny Annexe

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.

Tradesperson and Builder Costs

You should budget between £150 and £280 a day for a tradesperson to build your granny annexe. The individual's level of expertise will decide the exact fee you pay, the complexity of the project, and your location in the country.

Builder day rates, for example, are higher in London and the Southeast.

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.

Plumber Costs

Depending on the extent of the plumbing required for the project, 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.

Electrician Costs

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.

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 Starts

• 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 tradesmen 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.

Building Regulations for a Granny Annexe

There are several building regulations a new annexe needs to comply with. These include:

• Thermal Performance (Part L)
• Ventilation (Part F)
• Fire Safety (Part B)

Your design must demonstrate compliance with these requirements to obtain Building Regulations approval.

Planning Permission for a Granny Annexe

Obtaining planning permission for your new garden granny annexe will no doubt 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.

There are several building regulations and licenses available. Some temporary structures, including those that are unoccupied and used for purely leisure activities, may not require planning permission.

Many annexes will, however, require planning permission, especially if they’re self-contained or could be considered a separate dwelling. So a granny annexe with a person living in it will often require planning approval or a Certificate of Lawfulness from your Local Planning Authority (LPA).

The Caravan Act allows you to apply to site a temporary structure on the land rather than develop it. This isn't applying for planning permission; however, it will still require a License of Lawfulness from your Planning Authority. Just be aware this alternative route is not a guaranteed loophole.

Via this option, you can collaborate with the planning authorities directly, although they will have a say in the size and style of build they are happy to approve.

We recommend the normal Householder's Planning Application route for Granny Annexes that are considered "straightforward" during an onsite consultation. This is the same type of planning approval you would apply for if you had been building an extension or other work, such as an area with a raised decking.

Some Local Planning Authorities will request a Full Application if they consider a Granny Annexe a new dwelling. However, 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 requirements of your Local Planning Authority, including the concerns raised by the Local Planning Office in charge of your application.

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 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 multigenerational 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 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, as well as some companies will even let you design your annexe.

A prefabricated granny annexe is delivered with all necessary fixtures and is assembled onsite. 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

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.

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

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