Thinking of Building a Granny Annexe? Everything You Need to Know
Thinking of Building a Granny Annexe? Everything You Need to Know
Building a granny annexe can be a great way to create additional living accommodation without having to move house. But before jumping in, there are a few important things to consider.
Do you need planning permission? How much will it cost? And which type of annexe is best suited to your needs?
We've put together this guide to explain the different options available and answer the most common questions about building a granny annexe.
What Is A Granny Annexe?
A granny annexe, also known as a granny flat, granny pod, or garden annexe, is additional living accommodation within the grounds of an existing residential property. Unlike a standard garden room, a self-contained annexe is designed for someone to live in, with its own kitchen, bathroom, sleeping area and essential utilities.
Despite the name, granny annexes aren't just for elderly relatives. They can also provide independent accommodation for adult children, family members with disabilities or additional needs, or even to rent out for additional income. They can be attached to the main house, built separately in the garden or created by converting an existing garage or outbuilding.
Can I Build a Granny Annexe in My Garden?
In many cases, yes, provided you have sufficient space and can obtain the necessary permissions.
The main considerations include the size and position of the building, access for construction, proximity to neighbouring properties, ground conditions and connections to water, electricity and drainage.
It's also worth considering how much garden space will remain and how easily the occupant will be able to access the main house.
Do I Need Planning Permission?
A new, permanent, self-contained garden annexe will generally require planning permission in England.
Although many ordinary garden buildings can be constructed under permitted development rights, these rights don't generally cover the creation of separate, self-contained residential accommodation.
Your local planning authority will consider the proposed building's size, appearance, position, impact on neighbours and relationship with the existing house.
An annexe intended to remain part of the existing household may be assessed differently from a completely independent dwelling, and planning permission may include conditions restricting its future use.
An attached annexe built as an extension to the main house may have different requirements. Some extensions fall within permitted development rights, but this doesn't automatically permit the creation of a separate home.
If you're unsure, contact your local planning authority before starting work.
Do Granny Annexes Need Building Regulations Approval?
Yes. Permanent residential annexes will usually need to comply with Building Regulations, which cover structural stability, fire safety, insulation, ventilation, drainage, electrical safety and other essential requirements.
Building Regulations approval is separate from planning permission, so obtaining one doesn't automatically mean you have the other.
What Different Types of Granny Annexes Are There?
Traditional brick-built Annexes
Brick-built annexes are constructed using the same methods as traditional houses, offering a solid, durable structure that can be designed to match the existing property. They provide plenty of flexibility in terms of size, layout and appearance.
However, they're often the most expensive and time-consuming option. Bespoke designs usually require architectural drawings and structural calculations, adding to the overall cost. Traditional foundations also involve substantial excavation and concrete work, while constructing the building on site can mean months of noise, mess and disruption.
Timber-framed Annexes
Timber-framed annexes use a wooden framework with insulation and external cladding. They're generally lighter, quicker and potentially cheaper to construct than traditional brick-built annexes.
However, not all timber garden buildings are suitable for permanent residential use. They must meet the relevant Building Regulations, including insulation, fire safety and ventilation requirements, so simply adding a kitchen and bathroom to a standard garden room isn't enough.
Timber also needs protection against moisture and rot, and may require ongoing maintenance.
Modular Annexes
Modular annexes are constructed using pre-manufactured components that are assembled on site, significantly reducing construction time and disruption compared with traditional brick-built annexes.
Many modular systems use lightweight materials and can be installed on ground screw foundations, reducing the need for extensive excavation, heavy machinery and concrete. This makes them particularly suitable for properties with limited access.
Modern modular buildings can also offer excellent thermal efficiency, with high-performance insulation and relatively slim wall structures that maximise usable internal space. A choice of external finishes means they can be designed to complement the existing property.
However, not all modular annexes are built to the same standards. Construction methods, insulation levels, materials, specifications and warranties can vary considerably between manufacturers. It's important to research different systems, check that they're suitable for permanent residential use, comply with relevant Building Regulations, and read independent customer reviews before making a decision.
How Much Does a Granny Annexe Cost?
The cost of building a granny annexe can vary enormously depending on its size, construction method, specification and location. At the time of publishing (October 2026), estimates from a range of online sources vary from around £40,000 to £120,000, largely due to differences in building size, construction methods, specifications and what's included in the price.
When getting a quote for an annexe, it's important to understand exactly what's included. Some companies may advertise or quote a price for just the building shell, while others may include some or all of the additional costs involved in making the annexe ready to live in.
Additional costs may include:
- Planning applications, Building Regulations approval, drawings and surveys
- Groundworks and foundations
- Electricity, water and drainage connections
- Kitchen, bathroom and heating installation
- Flooring, decoration and internal finishing
- Landscaping and access paths
- VAT
One point that many sources agree on, however, is that modular annexes can be considerably more cost-effective than traditional brick-built alternatives, particularly when reduced construction time and groundwork requirements are taken into account.
You can find out more about modular annexe buildings on our Leka Xi Modular Annexe Buildings page.
Granny Annexe FAQs
Which Type of Granny Annexe Is Right for Me?
A granny annexe can provide valuable additional living accommodation, whether you're planning for an elderly relative, helping an adult child gain independence or accommodating someone with additional needs.
The best solution will depend on your available space, budget and intended use.
Here at Warm Roof Division, we offer Leka XI modular buildings in a range of designs and finishes. Visit our Leka Xi Modular Annexe Buildings page for more information, or to get an instant online quote.