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A Useful Guide to Surveying your Garden for a Granny Annexe

Over the last few years your Local Planning Authority will have seen an increase in the number of Planning Applications for Granny Annexes in back gardens.

In fact some Local Planning Authorities have issued guidelines as to what they consider an annexe to be.

(As with all Local Planning Authorities, this can vary from LPA to LPA and is open to the interpretation of any particular Planning Officer within any LPA).

For example, if you head to Canterbury Council’s Policy Page you can see first hand that they have a Policy for Secondary Dwellings (Granny Flat) Policy which is a PDF document that outlines what their interpretation of an annexe is.

In addition all annexes are only ever granted permission as being part of the main house and they can never be sold off separately.

They should only be occupied by a member of your family and as you have probably found (if you are reading this) they offer very attractive affordable housing solutions to a number of every day situations we have as families today including:-

  • Elderly care needs, for when your parents need part-time or full time care
  • An alternative to Care Homes (currently costing around £1000 per week in the UK)
  • A new lease of life for many who have lost their partner and feel vulnerable and lonely living on their own
  • A helping hand to family members who would benefit from a release of equity if Mum, Dad or both choose to downsize.
  • A first home for many young people today trying desperately to save up for a deposit to buy their first home.
  • An alternative to living back at home after a divorce, separation or illness creates a significant life-change that results in having to start over.

So if you want to make sure all those plans you have for an annexe in your back garden are feasible, and to make sure you are off to a good head-start, download our How To Survey Your Garden Checklist that goes along with this handy article.

Why The Size Of Your Granny Annexe Matters To Your Local Planning Authority

We frequently meet people who have great ideas about building a fantastic Grand Designs style annexe with two bedrooms, en-suite bathroom, utility, full kitchen, bi-fold doors and spectacular living area. (In fact our new Wheatley Extra Plus is almost exactly that!).

But if you have an average sized garden and a house with an extension it’s going to be a straight “No!” from your Local Planning Authority for your annexe because of it’s size, it’s facilities and how much of your overall garden footprint is already taken up.

An annexe has to be considered ancillary and subordinate to the main house. (You simply can’t build an annexe that’s bigger than the footprint of the main house.)

Action point: – Get some graph paper. Find out (or measure) the overall footprint of your main house and garden area (you can usually find this on a site location plan or in your house deeds and plans) and plot them out on the graph paper.

Add in the overall footprint of the iHUS annexe you are thinking of having.

If you have LESS than 50% of your garden area left once you have added your annexe to your plan it’s probably too big.

When Should I Consider A Flat Or Pitched Roof?

When we ran this simple question past our Facebook page audience a few months ago we were awash with comments about pitch roofs versus flat roofs with the vast majority in favour of pitched roofs.

Our standard roof finish across all iHUS Core annexes is a flat EDPM rubber membrane roof. The system is laid at a 1.5 degree fall for drainage, offering a watertight and durable roofing solution that will stand the test of time.

But for kerb-appeal and “prettiness” most of us love the pitched roof look to complete that little cottage look and feel of living at the bottom of the garden.

If you have a very overlooked site and a pitched roof will be obstructing neighbours light and privacy your Local Planning Authority is likely to recommend a flat roof to alleviate any neighbouring property issues.

Our best advice is to stay open-minded to both.

If you have a totally private garden and are not overlooked, and there are existing pitched roof outbuildings in neighbouring gardens then it is much more likely that a pitched roof will be seen as more in keeping and more favourable.

Action point:- View your garden and surrounding neighbouring properties from where you are thinking of siting your annexe. Turn 360 degrees and make notes of everything you notice, whether it’s trees, buildings, neighbour’s windows, neighbour’s extensions etc.

Ask yourself what would you be happy with if you were them?

Which Mains Services Do You Need To Connect To?

Annexes are considered ancillary to the main house and as such must be linked to the main house in some way.

This is usually (in part) by connecting the annexe to the main house water supply, sewerage and electrics.

So let’s look at these vital services in more detail so that you can be confident in this area too.

All Electrics Must Meet Building Regulations For Fire And Safety.

The electrical supply to your annexe will come from the main house.

And although the annexe will be isolated from the main house in terms of supply (so that we don’t overload either the annexe or the main house if everything is on and working at the same time,) you may need to upgrade your existing fuse board if there is an insufficient electrical supply in terms of power to the annexe or if your fuse board is not up to current Building Regulations standard.

A good guide for this is whether you have recently had any new electrical upgrades or installations or had a rewire as this may have highlighted any potential problems.

All our electrics must pass Part P Regulations for safety reasons.

According to the Electrical Safety First website;

“In 2005 the Government introduced electrical safety rules into the Building Regulations for England and Wales. Because of this, most fixed electrical installation work in homes must, by law, meet the Building Regulations.

Part P states that anyone carrying out electrical installation work in a home must make sure that the work is designed and installed to protect people from fire and electric shocks.

Part P applies to any changes made to existing installations, including any parts that have been rewired. In April 2013 further changes were introduced, reducing the range of electrical installation work that is notifiable – removing some requirements in kitchens and outdoors.”

You can find out more about Part P by visiting the Government website https://www.gov.uk/government/publications/building-regulations-part-p-electrical-safety-in-dwellings

To give you peace of mind, we’ve not found one yet that we haven’t been able to resolve in one way or another and as a general guide you can expect to pay less than £1000 for a new fuse board depending on what is required.

We can also fit a counter metre in the annexe for a small additional cost that allows you to calculate how much electric the annexe is using so there’s no fighting over the next electric bill.

Action point :- Locate your electric fuse box and measure the distance from your fuse box to the middle of the proposed annexe location. We include 10 metres within the price of the annexe with an additional cost per linear metre if required.

What About Water & Sewerage?

Connecting to your mains water is usually straight forward if we have good access to your existing drains.

It is likely that you have several manholes located around your property and you may even have lifted one or two in the past.

For the vast majority of us, it’s not something we have any knowledge about and we may not even know which manholes are for our mains sewerage and which are for rainwater.

For the purpose of connecting your annexe to your mains water, locate and find your nearest water pipe outlet. (This may be your kitchen or utility on the back of your house or it may be a bathroom.)

For locating your sewerage manhole the location of an existing bathroom is going to be helpful to you as it will already be connected to your mains sewerage.

In an ideal world we need your mains sewerage to have a fall of at least 1 in 40.

If you have a deep main sewer this fall may already be available.

If there is no fall (for example if the garden is flat) you may require a pump system or a septic tank. (Either of these options is an additional cost of around £5000) and don’t worry we can do all this for you as part of the service if required.

Action point: Locate and mark your mains sewer manhole if you can and make a note of any external pipes that are connected for water purposes. Measure the distance of these to your proposed annexe. (We allow the first 10 metres within our prices, any additional work required is charged per linear metre.)

Should I Tell My Neighbours?

It’s a very good idea to let any immediate neighbour know that you are intending to build an annexe for a family member in your back garden before we apply for Planning Permission and they get first notification from your Local Planning Authority.

Most neighbours will be concerned about a loss of privacy or the annexe blocking their existing view.

If you are on good terms with your neighbours, it’s best to listen to their concerns and address them where possible (it may be a flat roof versus pitch roof option) or placement and location of certain doors and windows and the inclusion of obscure glass where required.)

Annexes in general can only be decided on Planning Law not just because a neighbour objects. However it’s best to take into consideration any potential issues before the build itself where possible.

Action point:- Talk to your nearest neighbours about your project to gauge if they have any particular issues.

Trees, Bats & Other Protected Wildlife. Listed Buildings, Conservation Areas & Areas Of Outstanding Natural Beauty.

The United Kingdom is a very beautiful place to live thanks to our planning laws prohibiting us from destroying it’s beauty in the name of progress.

So if you live in a Listed Building, a conservation area or an area of outstanding natural beauty your Local Planning Authority is going to have very strict policies in place of what you can and cannot do.

One of most endearing annexes is the Aldridge annexe (pictured above) which is in a conservation area and looks picture postcard perfect because the Local Planning Authority stipulated the materials we used to ensure it didn’t look out of place.

If you have trees with preservation orders on or are surrounded by trees with root systems that may be disturbed your Local Planning Authority may request a tree report at an additional cost.

They are also going to protect any birds, bats or other wildlife they feel might be affected by the position or building process of your annexe.

Action point: – Find out if you have any potential factors such as wildlife or conservation that can  potentially affect your planning permission from being granted.

Access For Deliveries, Skips And Machinery.

Once we have successfully obtained planning permission for your granny annexe, carried out our full site-survey and planned your build, we will start delivering and building your annexe.

Firstly we need to get to your home with diggers, lorries and in some cases a crane.

The good news is all of those delivery vehicles and machinery come in a variety of sizes depending on the access.

So it’s a good idea to think about the best route for deliveries and access to offload everything as early in the process as possible.

We will also require skips on site during the build and will provide a portable toilet for our installation teams.

A side gate to the back garden is typically our access point for most annexe sites.

Action point:- Think about the road access to your home and any narrow lanes, low bridges or problems you’ve already had with deliveries. Also make a note of all access points to the proposed site of your annexe for deliveries during the build.

Previous Planning Permissions & Extensions

Have you already applied for and been refused planning permission for an extension, annexe or other build related application?

We will carry this out as part of our Planning Services, however it’s best to know if there have been any objections to previous applications or refusals and reasons for them for us to best advise you on the best course of action to take with your annexe.

Action point :- Find out if there are any historical planning application refusals on your home (even if they were with a previous owner.)


Planning an annexe in a back garden is a complex and major project to undertake. If you need any help we are right here ready to offer the best advice to you and we can help you survey your garden like a pro with our free on-site consultation services.

Or simply call us for a quick chat on 0808 164 11 11 and we’ll be happy to help.

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Download our iHus annexe brochure

If you would like to download our annexe brochure, please complete the form below. You can also request for a hard copy to be posted to your home address. Have any further questions, why not request one of our team get in touch?

If you would like to download our annexe brochure, please complete the form below. You can also request for a hard copy to be posted to your home address. Have any further questions, why not request one of our team get in touch?


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