If you want to add more space to your home and remodeling or converting existing space just isn’t going to cut it, then you might be considering extending. Also, it is often more economical to extend your existing home than to move (once you factor in agent/legal fees, moving costs, stamp duties etc).

This beginner’s guide covers common questions about extensions, such as:

Why Should You Extend Your Home?

Moving house costs money – there are agent fees, legal fees, stamp duty, as well as the premium for that desired extra bedroom or bigger kitchen-diner. And for the same price, you might well find that you can build a decent extension, adding both space and value to your existing home in the process.

Cantilevered extension to converted barn

A dramatic cantilevered extension has transformed this stone barn conversion

What Do You Need to Consider Before Extending?

It is worth thinking about your extension from an investment point of view. And as with all investments, you will want to see a return. Will your added space add value to your home? Normally it will, but there will be a ceiling price for properties in your area and you need to be mindful of the stage where it does not make economical sense to add an extension.

Also, if you are going for a single storey extension, it is worth seriously considering what benefit you could get from a two storey extension – if you are going to be building anyway.

There are also practical issues to consider that are not directly concerned with the construction process. Access is a good example. If you add to your accommodation, will it mean more cars will need to be parked on the drive? If you have no drive then the lack of off-street parking might be a reason for the refusal of planning permission.

Similarly, if your house is in a terrace do you have rear access for the unloading of building materials or if not, will you have to bring everything from beams to blocks, and girders to guttering through the house?

Other important aspects to consider before you get to the stage of getting your plans drawn are matters like:

  • soil conditions on the site
  • services
  • surrounding trees
  • any history of flooding
  • rights of way.

Another wise move is to get to know someone who has done a similar extension. They might have a builder or particular tradesman to recommend (or not recommend) but either way they will be full of useful tips on how long to allow for different tasks and many other matters.

How Much Does an Extension Cost?

The cost of your extension will be affected by many variables, from soil type (which impacts the foundations); whether you are building a single or two storey extension; what the extension will be used for; to how much glazing you plan to specify.

Depending where you are in the UK, for a straightforward extension you should allow around £1,000–2,000/m². Remember that the standard of specification you choose will have an enormous influence on the build cost. Experienced renovator Michael Holmes, says a single storey extension will cost the following per/m²:

  • Basic quality £1,000 to £1,680
  • Good quality £1,680 to £1,920
  • Excellent quality £1,920 to £2,160

A two storey extension will not cost much more per square metre because, aside from the extra interior fixtures and finishes, you are only adding walls and floor joists — a roof and foundations are required whether your extension is single or two storey.

Remember: Balance the amount you are willing to spend on your extension with the estimated value it will add to your home.

Single storey extension to brick property

The ambitious and well-thoughtout kitchen extension project has improved this home’s suitability for modern life

How to Finance Your Extension

There are several options when it comes to borrowing money to finance your extension. However prudence is the watchword — if you borrow more than you need you might do unnecessary things in the course of the job and have difficulty paying it all back. So always be conservative.

In an ideal world, we would all finance our projects using our savings, but with recent times having offered poor interest rates, the financial landscape has been one that favours borrowers over savers. If you need to borrow the money, your best options are:

  1. Credit card: If you need to borrow thousands rather than tens of thousands for your work, an interest-free credit card is a good choice. Shop around — the best deals offer up to 27 months of zero-rated spending.
  2. Loan: Personal loans of up to around £25,000 are suited to smaller projects. The loan may be enough to cover the building work and if you are fitting kitchens or bathrooms in your extension you can often buy these on finance from larger stores. Just keep an eye on repayments as they can quickly add up when you borrow from several sources.
  3. Remortgage or secured loan: If you are borrowing more than £25,000 you may need to remortgage your home or take our a secured loan against your home. Many building societies offer what is known as a Home Improvement Loan of up to £200,000.
Side extension to stone barn

A contemporary timber extension provides a great contrast to the more traditional granite farmhouse


Your builder will generally stage payments for each phase of the project. Try not to make any payments upfront. If it is necessary to purchase an expensive item perhaps a bathroom suite some months in advance of its installation, you should make sure it is in your name and not that of the builder, just in case they should go out of business. If necessary you should go to the place where it is stored and make sure the ownership is transferred to yourself.

Your designer will charge fees according to the work involved, so an accurate quotation of the fee would be a very useful thing to have before you give the go-ahead for plans to be prepared.

It is wise to check what any quote includes and who will pay any local authority application fees. Also, ask if any provision has been made should structural calculations be required.


VAT is zero-rated on new build in domestic properties including self builds, but this does not include extensions.

If you are renovating or extending a property that you can prove has been empty for 2 years or more, it will be treated as a conversion and therefore be charged at the reduced rate of 5%. The VAT concessions are only available via a VAT registered contractor.

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What Insurance Do I Need if I am Extending my Home?

If you are carrying out extension works and are managing the project yourself, you should arrange Extension Insurance to cover the new works and the existing structure. This is because most home insurers will exclude loss or damage whilst the property is undergoing alteration or renovation.

It’s worth discussing your project with a specialist site insurance provider like Protek as extension projects can be complex and often include liability assumed under the Part Wall Act 1996.

Site insurance caters for both the existing element of the property that’s being extended and all the new extension works that go into the process. The existing structure is usually your house – so if the property collapses while creating a new opening for example, the renovation insurance will cover it and completely replaces the requirement for buildings insurance, which is not suitable.

All the works, including any temporary works, materials, plant tools and equipment need to be covered. Public liability and employers liability is automatically included to ensure you are adequately protected.

You may also need to consider a 10 year structural warranty on the new extension works.

Extension insurance needs to be in place from the moment you plan to start works on the property and should continue to the point the project is completed and taken into full use.

Will I Need Planning Permission for my Extension?

Planning consent may or may not be required for your proposed extension. Under the Permitted Development Rights system a large number of home extensions can be built without the requirement of planning permission.

  • You can extend a detached dwelling by 8m to the rear if it’s single storey or 3m if it’s double
  • There are height restrictions. A single storey extension not being higher than 4m in height to the ridge and the eaves, and ridge heights of any extension not being higher than the existing property
  • Two storey extensions must not be closer than 7m to the rear boundary
  • It must be built in the same or similar material to the existing dwelling
  • Extensions must not go forward of the building line of the original dwelling
  • Side extensions must be single storey, maximum height of 4m and a width no more than half of the original building
  • In Designated Areas side extensions require planning permission and all rear extensions must be single storey
  • An extension must not result in more than half the garden being covered
  • You can only do it once and the original building is either as it was on 1st July 1948 or when it was built. In Northern Ireland it is as it was built or as it was on 1st October 1973

You should bear in mind that if your house is in a Conservation Area or a National Park, the amount of work one can do under Permitted Development is usually reduced.

Your local authority has the power to remove Permitted Development Rights if it feels the character of the area wll be threatened by any new work. If in any doubt, you should check with your local authority planning department.

If you are doing an extension that will need planning permission, it is wise to pop into your local planning office to find out informally what might be permitted — especially if you are planning anything out of the ordinary. It is always wise to research the local planning policies so that you will be aware from the start that an uphill struggle awaits you if you plan anything too exotic in the area where your house is situated.

Contemporary single storey extension to Victorian home

Despite being on an awkward corner plot, these homeowners have added a strikingly contemporary and contrasting extension to their Victorian home

Listed Buildings

All alterations to listed buildings, including internal ones, require consent and it is a criminal offence to alter a listed building without this consent. With a listed building the planners will always regard the existing property as more important than what you are proposing to add to it. Any extension will therefore have to respect the flavour, appearance and historic material used in the construction of the original house.

Depending on the size of the extension you propose, you might need planning permission as well as listed building consent to make your alterations.

Local Authority Grants

Unless your house is in an exceedingly poor state or is listed Grade I or Grade II*, or you are disabled, you are likely to have great difficulty in obtaining a grant for your work. However some organisations will offer help to maintain a period property (usually only to bring it to a basic standard of living to avoid demolition), so enquire with your local authority.

Building Regulations

Regardless of whether your new extension does or does not require planning permission, it will need Building Regulations Approval. Building regulations are rules approved by Parliament laid down to ensure the mimimum design and construction standards are achieved. These cover all manner of subjects such as fire and other forms of safety, insulation, the drainage system, and access.

Building control officers do not supervise work on your behalf. Their role is to ensure the minimum standards of the building regulations have been adhered to.

To meet Building Regulations you either:

  • Send what is called a Full Plan Submission to your local authority. In this case you pay a fee and the building inspector visits the site at the various stages of the build and inspects the work as it proceeds
  • Submit a Building Notice. This is a statement in which you inform the council that you will be complying with the regulations in building your extension and gives the building control department 48 hours notice of your intention to start the work. Surveyors will come and inspect the work at various stages and will advise you of any problems

The second method carries an element of risk because you do not have the benefit of an approved plan to work to and the building control surveyor may only know after you have contravened a regulation requirement. It could therefore prove to be an expensive way to build if problems are discovered that have to be rectified.


Getting a warranty for your extension is advisable as it will cover you for things such as structural defects or faulty workmanship. Should the worst happen, the builders who did the work will need to return to put right what has gone wrong.

How to Design an Extension

Many people design their own extensions, using structural engineers for advice. Others use a design and build company who can take on the whole project.

Side extension to stone property

This larch-clad extension has provided much needed extra space in this converted barn

The advantage of hiring a professional to do the design work, is that they might be able to visualise the space in a way that you had not thought of due to overfamiliarity with the existing layout of your home. It is also advisable to work with a professional designer with experience in the area if you are extending a listed home or a home in a Designated Area.

However, there is plenty of advice and inspiration for anyone who does want to take on the design work themselves.

Using an Architect

Many extensions or alterations to period or listed properties may benefit from the expertise of an architect. However if your extension is small scale many RIBA architects would probably say you would be better off with an architectural technologist who may have studied as an architect but not complete all the examinations. To be able to call yourself an Architect you have to pass the RIBA Part111 Professional Practice Examination, which is the final stage of training.

Finding an Architect or Designer

Choosing the right person to draw up your plans is as important as choosing the right builder, and the prospect can be just as daunting. Most people extending their homes are doing so for the first time and the natural tendency is to invest an awful lot of trust in the person who is charged with the key task of designing it.

Like builders, house designers do not have to be registered. When seeking a house designer you may find some you talk to have an engineering background and have worked as draughtsmen for local authorities or engineering concerns.

Design contacts:

Most of these bodies require full members to have relevant academic and technical qualifications. Whichever designer you choose, ensure that they carry sufficient professional indemnity insurance.

Updating the Access

Access problems can be a nightmare if you are extending. The issue usually raises its head in towns or on bends in the highway.

The scenario is that more bedrooms mean more bodies and so probably more cars. If your house is in a town and there is a shortage of off-street parking it might be a requirement that you provide parking space on your land.

If this worries you, remember that you do not need planning permission to provide a new access off an unclassified (i.e. lower graded than a B) road. Fortunately an awful lot of suburban roads come into that category.

Building an Extension

Who Will Manage the Work?

Early on, you will need to decide who will manage the build of your project. If the work is carried out by a design and build company, this will be managed for you, but if you have designed it yourself, or used an architect, you need to find a main contractor to pick it up from here. Alternatively, you might choose to manage the build yourself hiring subcontractors for each stage. Instead, you could hire a project manager to take on this role for you.

Finding a Builder

If there is one thing that is more difficult than finding the right builder, it is getting on with him throughout the project. Time and time again it is the human element that fails. Put simply: can you get on?

Obviously a good recommendation helps, but it is wise to talk to previous clients of the builder. You should also ensure that they have contractors all risks insurance.

If the builder has sufficient information there is no reason why they should not be able to give you a fixed price detailed quotation. Day work rates can be a recipe for disaster for all sorts of reasons. Try to avoid them except for extras requested at your behest although sometimes it is impossible to do so.

If VAT is to be added to the price given, make sure any quotation has a VAT registration number on it and a VAT receipt is provided when payment is to be made. It has been known for some less reputable operators to use the VAT system as a means of adding more onto the bill which they then keep for themselves.


It is enormously helpful if you manage to find a small group of tradesmen, all of whom have several trades under their wing. This can be crucial in keeping continuity. Time wasted can prove very expensive for a variety of reasons: e.g. scaffold and plant hire, additional labour and rent.

You should also remember that anyone hiring his/her own labour effectively becomes the builder. There is no contract with a main contractor and the buck stops with you. If you take on this role, you will have to manage:

  • trades
  • materials
  • services
  • keeping the site tidy
  • relevant site insurances and public liability insurance.

Safety and Disruption on Site

The first rule to stay sane is to stay safe, and the way to do this is to have a strict regime with the builders. They will not thank you if you are under their feet all the time, so here are a few suggestions as to how to remain both safe and sane.

Try to keep the mess to a minimum. You can do this by:

  • Using masses of protective plastic sheeting wherever appropriate
  • Sealing off the rooms being worked on.
  • Provide welfare facilities (rest area, toilet and access to a kettle) for your builders.

Should You Move Out While Extending?

If the builders need to have access to every room the best way to preserve your sanity and keep the project on track, is to seal yourselves off as far as possible for a few months. However not all extenders and converters are able to do this and if children are involved it is often best to let discretion take the better part of valour and move out for a few months.

This is particularly so if the extension is in fact a complete remodelling and the builders are working on the whole house. One option used by many is a caravan in the garden. It can be a cheap option and allows you to stay on site.

Renting rooms locally is a costlier alternative but might be necessary if you have children. If you are not too far away you can still keep your finger on the pulse. Going on an extended holiday and leaving the builder unsupervised is not to be recommended.

Always factor the cost of accommodation into your extension budget.

Heating and Electrics

Extending Your Central Heating

Before you start work you should reassess your heating requirements and check if your existing system is large enough to cope with the extra rooms you intend adding. If your boiler does not have the capacity it might be more economic to add a second system rather than replacing the boiler.

You may well pay less in the long term by opting for a separate electrical system rather than having to fork out a large lump sum for a new boiler. Many people opt for electric underfloor heating or electric radiators.

If you are remodelling the entire house or a large section of it try to have all of the pipework and any other first fix work completed before starting on the plastering to avoid having to start hacking plaster off again.

Extending Your Electrics

If you are adding a kitchen to your house you are likely to have to add a circuit that goes directly from the distribution board. For any other work, unless it is very extensive, it is usually possible to extend the existing ring circuit.

Ring circuits are restricted to 100m² but any number of sockets can be provided on this system.

An extension will give you the opportunity to add to your existing power points. Many people in this position take the opportunity to replace single socket outlets with double ones and install outside lighting.

Articles like this Comments
  • Chris Garbett

    Hi. I want to extend the back of my house. I want to do a wooden construction to save cost. I will be building on top of solid decking that’s well built. I will be joking onto my side garage and next doors garage. The front of it will be white cladding or timber like in some of your photos on the website. I will have a felt roof sloping and French doors and a window. This will be built onto my brick house. My next door are ok with it so can I just go straight ahead. I know my limits on size. Any help appreciated. Thanks.

  • Chris Garbett

    Hi. Any advice on the above would be appreciated. Thanks.

  • Lindsey Davis

    Hi Chris,

    The question is whether you can do it under Permitted Development. It is hard to say going just off the information you have given as it is to do with widths, and how much of the space in your garden has already been used up by outbuildings or existing extensions. It also depends how close to the boundary it is. Whether your neighbours are happy or not is sort of irrelevant because the needs of future neighbours needs to be considered too, so building so near to the boundary may be an issue.

    My immediate concern would be about constructing an extension on decking. I would suggest you seek professional advice from someone who can advice on the structural needs.

    I would also recommend something more hardwearing than felt. It has problems from UV exposure and also the chippings often wash off and block gutters. The lifespan is only 15-25 years so it has the shortest life expectancy of roof coverings. Try a synthetic polymer which will last 25+ years of a Polymer modified asphalt which can last up to 60. They are more expensive, but it is a false economy installing something which you need to replace more often and which could cause other problems like blocked gutters.

    I would seek more advice on this if I was you. Contacting the local authority planning department would be advisable too.


  • Chris Garbett

    Hi. Thanks. My widths and length are ok and my garden size is ok. My next door have done the same as me. Roof materials I can change. I am getting advice on the decking. Thanks for the help. Does this info provide anymore help.

  • Mary Sunderland

    can anyone tell me where this extension is? I want this extension!!!
    Seriously – admin – can you give out the owners or builders details?

  • Lindsey Davis

    Hi Mary,

    The house is in Eskbank in Lothian, Scotland. Their architect was Craig Amy of Edinburgh: http://craigamy.com

    You can see more about this project here: http://www.homebuilding.co.uk/completedprojects/a-striking-cedarclad-extension-0


  • Mary Sunderland


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  • Patrick Taft

    Undoubtedly useful article for many however I must provide clarification as there are some untruths which are misleading:

    1. RIBA fees scales were abolished in 1982. So to say that fees scales are the reason why many do not choose architects for small projects is entirely false. Disappointing to see that a specialist website appearing to offer help is actually stating false information.

    2. Architectural tehnology is an entirely different discipline to architecture and it is incorrect to say that a technologist has pursued the same path as an architect only to not complete part three. Becoming an architectural technologist has a route of its own and there is no crossover.

  • Patrick Taft

    3. The article suggests that there are alternatives to architects that all provide an equally adequate service for designing an extension. This again is false and shows a real lack of understanding about the roles of the disciplines mentioned. A structural engineer is an expert in structure and absolutely the best person to provide information for all structural elements, e.g. beam calculations, foundation design, etc etc. A building surveyor is an expert in carrying out surveys, assessing construction defects, advising on building maintenance etc. However none of the above are architects! They are not designers and it is staggering how this article puts forward the notion that anyone of those disciplines can simply have a go at designing a building. This is why there are so many bad buildings and so many bad extensions out there. You wouldn’t let an orthopaedic surgeon operate on your heart would you! Architects do not proport to know all about structure, neither do they claim to be maintenance experts – so why is everyone all of a sudden an architect!?

    Sadly due to the abolition of the RIBA fees scales the fees of architects are very low – so you’re not going to save a huge amount in getting a non-architect to do the work. And more to the point – it is a false economy not getting the right person to do the job because ultimately it will not be anywhere near as good in every way!

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