The Ultimate Guide To Building A Granny Annexe In Your Back Garden

If you are thinking about building a custom build on site granny annexe in your garden, this ultimate guide will help you get things right, and give you some of the best tips and ideas based on our extensive experience in the field over the last few years.

We have successfully obtained permission to build Granny Annexes (not all for Grannies) in:-

Tunbridge Wells

St Albans

Weston Super Mare


Newcastle Under Lyme


Sutton Coldfield
Isle of Sheppey

Swafham, Norfolk

It has become our core business and has evolved very quickly from the traditional Swedish log cabin style mobile homes of a few years ago to modern, well insulated, stylish “mini homes” at the bottom of the garden.

It is one of the best ways to add value to your home and become the owner of the “hot property” for resale purposes because multi-generation and independent relative living is becoming one of the most sought after types of property available.

So if you are ready for the ultimate guide to building a granny annexe in your garden, here it is:-

Download our free brochure filled with garden annexe and lodge inspiration:

Start with obtaining the right permission to build from your Local Planning Authority

"Annexe planning permission"

Before you begin thinking about building a granny annexe in your garden you will need to obtain Planning Permission or a Certificate of Lawfulness from your Local Planning Authority.

If you intend to build an annexe in your garden that someone will be living in, it requires relevant permission from your LPA (Local Planning Authority).

Ignore it at your own cost and always remember planning permission for an annexe will only ever be granted for a family member.

It will also remain part of the main house and cannot be sold separately and if you are looking to build something to rent out (as a second income) you will need to apply for Planning Permission for Holiday Lets not an annexe.

Our success rate in obtaining successful planning permission or a Certificate of Lawfulness is currently in excess of 90%.

We offer a subsidized planning permission service or Certificate of Lawfulness service starting from £1,900 (*subject to our terms and conditions). In some cases we make a dual application. This makes it as easy as possible for you to successfully obtain the right permission for your annexe when you choose to have an annexe supplied and installed by Contemporary Log Living.

Understanding your service connections

"Kielder Custom Annexe"

Whether you are building a one or two bedroom granny annexe in your garden you are going to need water, sewerage and electricity.

It can be really easy to get carried away with all the fun design aspects of a self-build project but if access to mains water, electricity and sewerage are hundreds and hundreds of feet away from your site you will attract potential problems.

Annexes will need their own electricity, water and sewerage and depending on the site and your existing supplies, connecting to your existing drains, electric and water may well be difficult.

The annexe electricity supply will be isolated from the main house on its own circuit but you may need to upgrade your electricity supply and / or meter board.

Planning Authorities are also likely to insist on the annexe being as close to the main house as possible.


Annexes are going to be using the electricity supply from the main house but some supplies may need modifications or a new sub domain to feed the annexe independently.

If you get this wrong, you will end up potentially blowing all fuses in the main house and the annexe as it will be very easy to completely overload the circuit.

This is why building a granny annexe in your garden is beyond a DIY project you are going to need to bring in a team of experts if you are going to avoid mistakes that will cost you more in the long run.

This is so much more than simply converting an out building or thinking this is a Summer House, it’s a major project that should only be carried out by experts.


If you are fortunate, your new annexe will be right next to the mains water and if it is, it is relatively straight forward to connect to.

However most annexes are situated several feet (sometimes 20 feet or more) down the garden and connecting to the mains then becomes a major additional cost and consideration.

Your Local Planning Authority may also insist that the annexe is closer to the main house for it to be considered an annexe and ancillary to the main house.

Although there are pumps available on the market for less than £2,000 that will help with the water flow required for showers and baths, locating and connecting the water mains and electricity usually requires digging a substantial trench (at least 3 feet deep) the full length of your garden between the main house and the annexe.

This may require specialist equipment and tool hire or if your budget allows, you can get a specialist firm in to quote for these services using “moleing” equipment.

The service providers dig two large holes either end of the run of garden or site and send a “mole” underground using trench less technology as a way of installing new pipes, cables and ducts without the need for continuous trenches and disruption. 

*Expect to pay around £4,000 – £5,000 for moleing services for an average to large-sized garden.


We have used pad foundations for years and have successfully built buildings as large as 120 square metres as well as smaller annexes, studios and log cabins.

Not only do they save you potentially thousand’s of pounds when compared to a traditional concrete base, they are easily positioned on site, are fully adjustable and save on masses of tedious groundwork.

In a recent planning application where trees were an important part of the landscaping and root disturbance was to be avoided, we proposed these type of post foundations as the solution.

The Local Planning Authority agreed that these solved a lot of their issues and planning was granted.

With speed, ease of use and total adaptability, it is also a straight forward and easy to process to use the same system under decking, garden offices and studios and even commercial buildings where required.

All in all they are a complete win / win when it comes to creating foundations on a budget that won’t break your bank either.

**Your annexe will need decking, a ramp or steps to the front door and living areas using this type of foundation system.

If you choose to build a concrete slab instead, you will still need access steps or a ramp up to the front door and living areas.

brick-built annexe built on traditional footings would come under Building Regulations in addition to Planning Permission and would have VAT added, costing you an extra 20%.

It is highly unlikely you would get Planning Permission for a brick annexe, read more about that by clicking here.

Sizes and designs of granny annexes

"custom annexe"

The idea here is to successfully obtain planning permission to build a granny annexe in your garden and your Local Planning Authority is likely to look favourably upon what they consider to be a reasonable size annexe for dependent or family member living.

Whilst anything MAY be possible in a self-build home project, annexes can only be single storey and classed as ancillary accommodation to the main house.

"Rydal Custom Annexe"
You Choose the Design

*Your Local Planning Authority may ask for modifications to be made to any aspect of the design or finish you choose as part of them agreeing to grant planning approval, so be prepared to stay flexible.

Most of our customers like the open plan living style of lodges they have stayed in or seen at exhibitions and shows.

**We supply those too, which you can view here.

The main difference is that the Signature custom annexes we supply and build on site are best suited to gardens which cannot accommodate siting and access for a Residential Lodge style annexe. 

The construction of an on site build is perceived to have better insulation properties when compared to a Residential Lodge style mobile home or annexe, however the reality is that they are not really that different.

In November 2015 the new British Standard 3632 was introduced making Residential Mobile Homes suitable for year round living.

We add everything you would expect in a new home or apartment to our annexes, from fully fitted modern kitchens to fitted bathrooms, utility rooms and wet rooms.

The beauty of a purpose-built annexe is that you are immediately in charge of your own self-build project where you can literally select the look and style you want and we will incorporate it into your annexe for you if we can.

We offer a full turnkey service that takes care of everything for you from start to finish.

Included in the price of building a granny annexe in your garden will typically be:

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Your annexe will need to be structurally calculated in the same way as any a self-build home would be, taking into account load bearings and insulation, strength and other factors that will ensure your building is of the highest quality, extremely well insulated and built to last.

We undertake this for you.

All work that is undertaken on your property now comes under Health & Safety Regulations.

We will cover this for you.

Your Planning Permission or Certificate of Lawfulness will be applied for and dealt with on your behalf as part of the service we offer.

We will apply & deal with this on your behalf.

You will need a skilled installation team to coordinate the various aspects of the build including foundations, electrics, plumbing & heating, windows & doors, painting & decorating, carpentry & joinery, kitchen and bathroom installations and roofing, scaffolding and service connections.

We undertake full project management for you.

Our average build on site from start to finish is typically 8-14 weeks. (Some of our larger annexes may take slightly longer depending on the final specifcation and size.)

(As annexes are usually required for “homeless” relatives so to speak we know speed of build is important.)

Our expert teams usually have the building up and water tight within the first few weeks of the build. 

Any specification or aspect of the annexe that is important to you can also be adapted for a dependent relative’s special disability or needs.

We pride ourselves on our flexible approach.

Time scale and prices

"Foresters garden lodge"

Our custom annexes typically range from from between £95,000 – £175,000+ for the larger and more custom annexes we design and build.

Planning permission or a Certificate of Lawfulness will take 8 weeks from the time your Local Planning Authority validate the application (this can vary between 2-3 weeks depending on the workload of the Council.) We also need a few weeks to prepare your drawings and application before submission.

Our installation schedule is planned in advance and stays flexible to allow for house sales, moving time and equity release if required.

Obtaining a quotation from ourselves is a free site consultation service we offer and it’s the best place to start your annexe journey, even if you are just looking at annexes as an option.

"Ultimate Guide To Building an Annexe In Back Garden"
In Summary

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