3 Of The Most Frequently Asked Questions We Get Asked About Annexes Are:-

  1. What are the Planning Permission options?

  2. How are annexes constructed

  3. How much do they cost?  

If you have been following us for some time you’ll know we’ve been involved with annexes and annexe living since 2011 when we part of the Sales & Marketing team at the Ideal Home Show which featured a stunning Open Plan Contemporary style log home from Sweden.

Since then, we’ve been featured on Amanda Lamb’s My Flat Pack Homes TV Show, been featured at the National Home Building & Renovation Show & Grand Designs Live and spoken with literally thousands of people about the best way to go about building an annexe in the back garden.

We consider ourselves to be the best free advice you’ll get anywhere in the annexe sector and if you have a question, please feel free to contact us on the website or on our Facebook page if that’s easier for you.

So Let’s Talk About Costs And Some Of The Reasons They Vary So Much

We believe in the saying “You get what you pay for.

Whether that’s planning permission for an annexe by way of either a Certificate of Lawfulness or Householder’s Planning Permission or the type of annexe you are thinking of buying.

Annexes are a major purchase and should be considered as such.

Chances are they will be the second biggest purchase you make (after you main home.)

And therefore weighing up all the options available can be difficult for many people as it is not something many people have ever done before.

In fact if you say to someone this week, “I’m thinking of building an annexe in the garden for my Mum” you may well get a very puzzled look back at you with the question, “What’s an annexe?”

This may help to visualise what a modern day annexe may look like, we think they are beautiful 😉

Annexes Involve Every Trade A Full House Build Would Require

Why annexes cost as much as they do?

It takes a huge amount of time, effort & skill from multiple trades & people to either manufacture & build an annexe to your specification or to build an annexe on site in your back garden.

Here’s some of the key skills you will need for a successful annexe project:-

  • You will need the design skills of an architect or an annexe expert (luckily all of our Residential Mobile Home Annexes are architecturally designed and we’ve been designing them ourselves for years so we know what works and what doesn’t.)
  • The Planning skills of an annexe expert. (even if you choose the Certificate of Lawfulness route. It is still highly specialised). Without planning permission or permission to site an annexe in your garden you simply cannot proceed any further. (We have a very high success rate in achieving this for you.)
  • You will need structural calculations and a full electrical plan. (We offer these as part of our turn-key service.
  • Once planning permission is approved or a Certificate of Lawfulness is obtained you will need to prepare your foundations and connect to your mains services. (Again, we offer this as part of our turn-key service.) Annexes must be ancillary to the main house and share mains water, electricity and sewerage.
  • You will need an expert team to construct your annexe in SIPS (Structurally Insulated Panel System) which we recommend for our custom annexes / build on site annexes. Or an expert team to supply & fit a Residential Mobile Home to BS3632 standards. We offer both.
  • Following on from all that is the finishing of the build itself which will require roofing, “A” rated windows & doors, heating system or electric radiators, cladding, flooring, second fix joinery, kitchen, bathroom, plastering, electrics, heating, painting and decorating.
  • It’s an exhaustive list of skills & trades that combine to become zero rated for VAT when built as a turn-key service.
  • Most people quickly find their budget runs away with them if they try to source each element individually as they then attract VAT @ 20%. This makes it far less cost-effective than opting for an all encompassing turn-key service like ours.
  • You want to end up with a warm, stylish annexe that is great value for money & ticks all the boxes for the planners and for you as a family.

And That’s Exactly Where We Come In When You Book A Free On-Site Consultation With Us

"Book A Free On Site Consultation"

This Is The Dovecote As An Example Of How Annexe Living Today Can Benefit You & Your Family

To view more details about the featured annexe above click here.

How To Get The Best Price For An Annexe?

  • Google is one of the best inventions ever for researching and finding information about anything & everything today – but nothing beats talking to someone about your project. It is by far the best way to get a price for your annexe project and understand what’s involved.
  • Take online calculators with a pinch of salt, most of them do not factor in the man power or expertise required to build or manufacture an annexe.
  • Cost per square metre are only a guide as economies of scale, site specifics and location will all be a factor in your final quoted annexe price.
  • Be realistic with your budget. If you have a budget of under £50,000 in mind for a building the size of a small bungalow, fully fitted out with foundations and services connected you are not being realistic. (Our Minuet is the lowest budget annexe we offer at £44,403 (plus foundations, services & siting and delivery.)
  • Our entry level annexe is The Studio starting at £66,509
    (plus foundations, services & siting and delivery.)
  • Expect to pay between £75,000 and £130,000 for a high quality annexe build, either on site or manufactured and delivered. One of our most popular annexes styles & designs for this is the Burleigh which you can find more details on by clicking here.
  • If you have a budget in mind of £150,000 or more, you can expect to be able to push the boat out when it comes to what is possible with annexe design today.
  • With designs like the Hampton (below) starting at around £149,588 you can see exactly why more and more people are choosing annexe living today.

Important Considerations For Getting The Right Annexe At The Right Cost

  • Annexes are classed mobile homes whether they are built on site or built in a factory to British Standards. (The factory build options usually work out to be the most cost-effective & are certainly the least hassle for everyone involved.)
  • Annexes are classed as ancillary accommodation to the main house and are not a separate dwelling in their own right.
  • They can never be sold as a separate dwelling and will remain part of the main house at all times for use by a family member.
  • Building an annexe is often more cost effective than building an extension of a similar size. You often get a completed annexe (including kitchen & bathroom, decor, flooring and heating) included in the total overall cost of an annexe compared to an extension build cost that then requires fitting out. (There is a significant saving on VAT for example as annexes are Zero rated for VAT purposes.)
  • Flat roofs are more cost-effective than pitched roofs. (Most suburban gardens will need to have a flat roof if overlooked by neighbouring properties.)
  • One or two bedrooms is not an indication of price when it comes to an annexe. It’s size, specification and site specific factors that will determine your total annexe build cost.
  • Planning permission or obtaining a Certificate of Lawfulness is a cost that should be factored in to your budget. You simply cannot site an annexe in your garden without one or the other.
  • Although annexes have elements of self-building to them in terms of designing something “off-plan” and in every detail it’s NOT to be confused with building a Passive Hus in your garden. Don’t let that Grand Designs enthusiast in you get carried away with the wrong thing.
  • Factor in the hidden benefits of potential Inheritance Tax savings as a family, the benefits of having family members living together and the cost of Care Home care in the future as part of your overall cost. (For a great article from SAGA on more about the hidden benefits as a family when planning a granny annexe click here.

We can advise of actual costings and any discounts that may apply after our initial Free On Site Consultation.


  • You can get a guide to the true cost of building an annexe on Google but nothing beats a free on site-consultation where we can discuss everything you need to know, including the cost!
  • There are multiple skills & trades involved with annexe builds making them complex and a major construction for any annexe company.
  • Turn-key services like ours are the most competitive way to build an annexe.
  • Trying to cut corners and save a few quid here and there will inevitably lead to problems further down the line.
  • Don’t get carried away with self-building construction methods that do not apply apply to annexes. Annexes are well constructed, well insulated and built to last, keep your budget on track with the internal living space details instead.

As always we look forward to your thoughts and comments below or join in the conversation on our Facebook Page !

Use The Contact Us Page To Email Us With Your Enquiry

Pete Cossie, Contemporary Log Living

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