Extension Beginners Guide

2015-11-23 15.20.00 (2)

Recent figures from the Royal Institute of Chartered Surveyors (RICS) show that while the housing stock is growing there are fewer houses being bought and sold. People therefore are staying in their homes longer and, according to the RICS, they are moving on average every 14-and-a-half years far less frequently than was the case only a few years ago.

All of this means that more people are extending. In fact it is said that for every person who self-builds there are 15 that add extensions to their homes.

The reasons for all this are easy to see. It often makes more economic sense and is a better use of space. It means we can stay in the same neighbourhood if we like it and that the children can remain at the same school.

An overwhelming advantage of extending and not moving is the issue of stamp duty. It does not take a genius to work out that with stamp duty on the most expensive houses running at four per cent, by the time you have calculated the agents fees for selling your house and the stamp duty on the one you are thinking of buying, you might well find you could build yourself quite a decent extension for the same price.

The trick is to extend and to come out well in the investment stakes, which means you have to put a lot of thought into even the smallest extension. For example, if you merely wish to extend the kitchen at the rear of your 1930s semi, should it be single storey or two? If it is the latter, what will go above it?

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 and rights of way. Even then it might be 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.

In some instances it might be wise to ask your adviser to write to the local planners after any meeting you might have had with them confirming what was agreed. Providing it is written tactfully this should help pave the way and in a sense nail them to the mast, particularly if they show any signs of backtracking at a later stage of the process.

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.

Other important issues concern the person you will choose to design your extension, how much it will cost, and how much of the design (and the labouring) can you do yourself? Just as crucial is the style and feel of the extension you require. Are you really sure in your own mind that you know what this is? All of these issues plus many others are tackled below.

Planning and Building Regulations

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.

(MORE: Our Guide to Permitted Development Allowances)

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 PD 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.

However, if in any doubt, you should check with your local authority planning department.

Building Control

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. Most self-builders and extenders send what is called a Full Plan Submission to their 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.

The alternative is to 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. As with the Full Plan Submission method, surveyors will come and inspect the work at various stages and will advise you of any problems. However, there is an element of risk with this method 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 inadvisable and expensive way to build if problems are discovered that have to be rectified.


An alternative to the usual warranties available for building work which can also be applied to extensions, loft conversions etc, is the MasterBond warranty from the Federation of Master Builders (FMB), which has similar characteristics to the NHBC and Zurich registered builder schemes. MasterBond will cover works carried out by MasterBond Warranted Builders (note that not all FMB members are registered as Warranted Builders) against defects due to faulty workmanship or materials for two years from completion, (except for electro-mechanical items which are covered for one year only) and against structural defects for a further eight years. FMB require the building work to be notified to building control, who will inspect the work at stages dependent on the type of project.

The benefit of MasterBond passes automatically to new owners and the cost is 1.5% of the contract value, including VAT. MasterBond is subject to exclusion clauses and limitations, satisfactory for extensions, loft conversions and similar projects, but the financial limits of the policy may not be acceptable to lenders on new homes. Structural warranties for extensions are also available from project-builder-insurance.com.

Many people avoid using architects for smaller projects because of the RIBA scale of fees, which starts at around ten per cent. However on projects of less than £20,000 most architects prefer to charge by time, so if you choose an architect it is probably preferable to negotiate a fixed price if your extension is relatively small-scale and not a complete remodelling of your house.

Many extensions or alterations to period or listed properties may benefit from the expertise of an architect. However if your extension is small scale and does not involve a great deal of design input many RIBA architects would probably say you would be better off with an architectural technologist. A technologist may have studied as an architect but not completed 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. The title Architect is protected by law.

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. Others may be members of the Royal Institution of Chartered Surveyors (RICS) or theChartered Institute of Architectural Technologists (CIAT) or the Association of Building Engineers (ABE) formerly the incorporated Association of Architects and Surveyors. They could alternatively have a practical background and be a member of the Chartered Institute of Building (IOB) or the Institution of Structural Engineers (ISE).

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.

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.

The good news is that there is no VAT on approved material alterations to listed buildings. However the work must be carried out by a VAT-registered contractor and zero rated.

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.

The philosophy behind house renovation grants was to assist people on low incomes to bring what were known as unfit properties up to modern standards. Generally the grant awarded was 50 per cent of the cost of the work up to a maximum of £20,000. However over the past 18 months these have been phased out over most of the country and generally the only local authority grants available are historic building grants. In the case of Grade I and Grade II* properties these are awarded by English Heritage.

You are also unlikely to succeed if the house is less than 10 years old or you just want to increase your living space for example with a kitchen or lounge extension.

If your house is a period property, whether it is listed or not, some local authorities will give historic building grants. But even then there are many conditions. The first of these is that they are generally given for improvements to the historic fabric and not extensions, so unless your extension is needed to bring the property up to fitness standard i.e. it lacks the basic amenities of an indoor bathroom or toilet, you are unlikely to be successful. When historic building grants are awarded again they are entirely discretionary most local authorities will only award up to a maximum of around 25 per cent of the cost of the work

The only good news is that VAT registered contractors can zero rate invoices for material alterations that need listed building consent.

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.


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 the fee includes and who will pay the local authority application fees. Also, ask if any provision has been made should structural calculations be required.

Unless it is a short contract, stage payments will be on a monthly basis. 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 he 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.


Most architects will advise you to draw up a contract. Many favour the new JCT Home Owner Contract, available through RIBA bookshops (ribabookshop.com). This contract has a built-in retention clause designed to act as an incentive to the builder, plus a damage clause that enables the direct cost of any delays to be deducted from the final contract value. It should also cover the procedure to be taken should your builder go out of business in the course of building the extension.

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 exisiting 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, which may be only part way through its useful life. This may well be slightly more expensive in the short term but bearing in mind the payback period on a piece of expensive capital equipment like a boiler it may pay you to proceed in this way, especially if you feel you may not stay in the house forever. Not all electrical systems find favour with people extending their homes, however, as some have unsightly radiators. The alternative is electric underfloor heating.

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.