Planning Permission

What is planning permission?

Planning permission or planning consent is required in order to be allowed to build on land, make alteration such as larger extensions, or change the use of land on buildings. The idea is to govern what your building or house looks like on the outside, the impact it has on the street where it is located, and the uses to which the house and the land it occupies are put.

There are 111 classes of development including a vast majority of extensions that are granted an automatic planning permission these categories are referred to as permitted development.

In the case of any proposal there is therefore a two stage test” “is the proposal development at all?” and, if the proposal is development, “is it permitted development?” Only if a development is not permitted development would a full application for planning permission be required.

Planning should not be confused with the Building Regulations they are entirely separate.

Party Walls

The Party Wall Act 1996 introduced procedures which allows for and protects the rights of owners joined by a party wall.

The Act is not administered by any enforcement agency, but it places responsibility under law on the owners who may be party to the proposed works. If the Act is not followed, any court proceedings will take the provisions of the Act into account in additions insurers may well take non compliance into account.

For more information:

Building Regulations

What are Building Regulations?

The Building Regulations set standards to ensure people’s health, safety, welfare and convenience of people in and around buildings. They also provide for energy conservation, and inclusive access to and use of buildings.

They are technical in nature, and frequently updated.

Complying with Building Regulations is a separate matter from getting planning permission for your work.

For a more information on the Building Regulations please follow the following two links:

  1. Building Regulations Explanatory Booklet
  2. Planning Portal

Harvey Norman Architects is a member of the Local Authority Building Control’s (LABC) “Partner Authority Scheme” with South Cambridgeshire District Council.

How long will it take?

Building Time

The time taken to build your extension will clearly vary depending on the size and complexity of the project but also be aware that the following items will have an impact on the overall timing.

Pre-contract time

We would normally expect a period of 4-6 weeks from your confirmation for a builder to be able to start which will allow time to prepare any building contracts and sort out any final queries.


The weather conditions will clearly have an impact on the overall time taken to complete your building works. Certain activities such as brick laying and external rendering can not be completed in sub-zero or rainy conditions.

Builder’s Work Method/Programme

Some builders are a lot bigger than others and can build several jobs at a time whilst some will complete one project before moving on to another. The amount of resources a builder has available to use on your project will have an impact on the contract time. If, for example, you have an average of 4 men a day on site, your project will be built faster than if you have 2. There will come a point where you can have too many people on site and different tradesmen will just get in each others way.

Whilst builders can be reluctant to provide you with a simple programme of works, we would recommend that you ask for one so that you have a good understanding of the planned method of carrying out the project and overall contract time – we can provide a blank copy to be completed as part of our Builders Pack.

The programme is a good method of monitoring the progress of the works and will highlight any key activities that you need to know about such as breaking through into the existing property, payment timings and choosing fixtures and fittings such as sanitaryware and kitchen units.

Time of Year/Working Hours

Building in the winter months may affect the overall contract time due to lack of light although the effect of this could be reduced by using temporary lighting.

Access to Property

Most homeowners will be living in the house whilst works are being carried out but it may help the builder and speed up the building process if you could move out, even for a limited period during critical activities such as breaking through or demolishing existing structures.
If you have limited access to the area where the extension is being built, this could also prolong the building time if for example, diggers cannot be used.

Additional Work

Whether it is the discovery of unexpected additional work or you have asked the builder to carry out some extra items of work, this will normally add time to the overall project. It is unreasonable to expect the builder to complete the project to the original date where this occurs.

Late Delivery

Sometimes, through no fault of the builders, materials may not be delivered when they were promised and this will delay the works. This usually applies more to specialist purpose made items such as doors and windows, staircase, etc but be aware of delivery times of these items and make sure they are ordered in good time.

The programme of works is particularly useful for determining when specialist items will be required on site.


Whilst many of the above items could cause delays to your project, a well thought out and detailed project will minimize the risk.

Possible contract period for the extensions shown.

  • Small single storey extension 10 – 12 weeks
  • Loft conversion 10 – 12 weeks
  • Large single storey extension 12 – 14 weeks
  • Small / medium two storey extension 14 – 16 weeks
  • Large two storey extension or multiple extensions 20 – 24 weeks

Please note that these figures are illustrative only and do not include fees or VAT. They are not intended to be anything more than a helpful guide.

Finding A Builder

Congratulations! Your planning application is approved!

Once you’ve received planning permission for your house extension, Harvey Norman Architects will produce the detailed technical drawings and specifications required by your Building Regulations department.

You can also use these technical drawings to start obtaining quotes from builders.

Finding a builder can bring its own problems, so if you don’t have any particular ones in mind we will be happy to ask a number of trusted and reputable builders to provide quotes.

We will also help you find and brief any other 3rd party consultants that may be needed, such as a structural engineer or a quantity surveyor.

We recommend that you consider the following factors when finding a builder to undertake your work:

  • Price: not always the most important factor for some people, but clearly your builder must be able to work to your budget
  • Experience: can your proposed builder show you examples their house extension or loft conversion work?
  • Quality: if you can view examples, are they of a quality that you would be happy with?
  • Reputation: can you get positive references from people that have used the builder before?
  • Reliability: prior to starting, it’s hard to judge how organised and reliable your builder will be. So watch out for whether they turn up for your meeting on time, return your phone calls and submit quotes when they say they will.

Finding a builder is one thing. Managing your building project is another.

So once you’ve made your choice of builder, Harvey Norman can recommend a form of contract that sets out terms, timescales and conditions in the event that your builder overruns on cost or time.

Moving ahead with your build

Once you receive the go-ahead from Building Regulations, you’ll have the green light to let your builders proceed with your house build or extension.

When the building project itself starts, Harvey Norman Architects will monitor the building work at each stage, organise site meetings – which you can attend if you wish – and will keep an eye on the overall progress and development of the work.

Throughout your project, our aims will be to keep your stress levels to a minimum, ensure a smooth building project and to help you keep timescales and budgets on track.

Extension build costs

Extensions can add around 25% to value of your property, and basement or loft conversion will typically boost the property value by 10% to 15%. But what will they cost?

Providing costings for an ‘average’ extension can be tricky – since there really is no average! However, issues such as ground conditions, access to the site, location and proximity of services are a huge factor in the build budget; therefore in providing indicative costs, we have assumed that all of these issues are reasonable to deal with and that all the work is done by a main contractor.

Build Costs

The biggest variance in terms of cost comes from the individual specification, and how the budget is managed. Whilst our costs provide an indication of the variation between build route and extension size. There are so many choices available and therefore many decisions to be made, which can affect your overall budget, by a considerable amount. Over-spending on material specification is one of the most frequent reasons why extensions go over budget.

Standard construction, no significant structural issues, budget specification

£1,500.00 per m2

Standard specification some structural or site related complexity

£1,700.00 per m2

High quality materials or unusual specification challenging structural or site conditions

£2,100.00 per m2

(For loft conversions and internal work is cheaper and as such you should assume 60% of the above, however for basements the figures above need to be uplifted by a minimum of 50%)

Please note that these figures are illustrative only and do not include fees or VAT. They are not intended to be anything more than a helpful guide.

Basement Conversions


What do you do if you want to extend your home, but your garden is too small to allow it, or your loft is unsuitable for conversion? You may think the only way to get extra space is to move house. However, there is another possibility – excavating below ground to create a basement.

The major disadvantage of going underground is the cost, as conventional extensions are usually far cheaper to build. In areas where building land is scarce and property values high, basements can be an economic investment. If there is already an existing basement in your property – even if it’s in poor condition or with an unsuitably low ceiling – this will reduce costs and make a conversion more financially viable.

Design considerations

Basement extensions can offer interesting spaces quite different in character to the rest of the house. They make excellent games’ rooms, gyms or home entertainment rooms (the natural sound insulation that results from being surrounded by solid walls and subsoil make this an ideal application). Other successful uses include utility rooms and even swimming pools, budget permitting. It’s also possible to use underground rooms for bedrooms, as long as the occupants are happy with lightwells in place of windows.

Along with the lack of daylight, the main problem a basement designer faces is connecting the zone to the rest of the house. Ideally the new stairwell should link seamlessly into the hallway. The staircase must provide a safe and direct route outside from the new lower level – there may be problems with Building Regulations otherwise (although these may not apply if you are upgrading an existing basement). The best location for the staircase is immediately below the ground-to-first-floor flight. Locating it elsewhere will just eat into existing rooms, therefore reducing the project’s cost-effectiveness.

A popular way to get daylight into basement is with lightwells. These are pits dug around the outside walls of a basement to allow light to penetrate into the rooms below ground. Even a small amount of daylight can relieve the feeling of claustrophobia that may mar an otherwise successful basement extension.

If introducing natural light is not possible, a carefully planned artificial lighting scheme is essential to the success of the project. Lighting can be softened by concealing the source, and reflecting it off surfaces. This trick works well in basements and is an effective way of illuminating the ceiling. The lighter the ceiling, the higher it will seem.

The most simple way to construct a basement is to follow the line of the existing structural walls above (underpinning). However, it is also possible to extend horizontally beyond the footprint of the house. This can be particularly effective at the rear of a house, where it is usually capped with a raised terrace or patio. This allows rooflights to be set into the ground, which flood the rooms below with sunlight.

Planning issues

Permitted development rules do not directly deal with basements. Because of this confusion, it is a good idea to consult your local planners and find out their view at an early stage.

Building Regulation Issues

Building Regulation approval will always be needed for a new basement and for any substantial upgrading of an existing cellar. A major factor is how easy it is to make the walls watertight. This will depend on the nature of the ground around the house. Very well drained subsoil (that which has a high sand or gravel content, for example) is the least problematic, because any water will drain away quickly. Badly drained ground, such as heavy clay, will cause water to build up around the walls and create pressure on them, so careful design and construction is essential. If there is a high water table, or your area is prone to flooding, it’s hard to guarantee the effectiveness of the waterproofing, so basements might not ?be a sensible choice.

The structural design of the walls is probably the most important aspect of basement construction. The most common method used to creating them is called underpinning, where new reinforced concrete walls are built directly under the supporting walls of the house. The new walls are usually tied into a new concrete floor with extra reinforcement.
If you are close to your neighbours, their properties may be affected if the work is not carried out safely, so you may find that the provisions of the Party Wall Act apply. This requires that you serve neighbours with a formal notice before any work starts.

Another major concern is the ease with which you can escape from the basement in case of a fire. If it is not possible to fit any windows or doors that lead straight from the underground rooms to the outside, the only escape is going to be up the stairs to ground floor level. The regulations require that there is fire protection between the basement and the ground floor, and that once you reach the ground floor there is a direct escape route to the outside. As previously mentioned, this makes it inadvisable to locate a staircase away from the main hallway – especially if it leads to a high fire risk room, such as a kitchen.

Drainage for bathrooms, toilets and sinks also needs to be considered carefully. Because the basement floor is usually well below the height of the surrounding drains, a pump of some kind is necessary. The best way to tackle this is to fit an internal pump as close as possible to your appliances. The main disadvantages here are the noise caused by the motors and the need for regular maintenance.

Rear extensions


Rear extensions are often about establishing a better relationship with the rear garden.

Design Considerations

Victorian houses used to have their utility areas at the rear of the house and the result is for most houses the garden is cut off from the main living areas. Modern lifestyles and family living require that a visual and spatial connection is established between the kitchen/dining/living areas and the rear part of the house.

When designing a rear extension an architect will try to open up the rear wall, create sight lines, views and circulation paths between the internal and external spaces. A design of a home rear extension could be kept traditional and in-keeping with the character of the existing house or flat. Alternatively a rear extension can be a modern looking addition that establishes a dialogue between the existing house and the new addition. An architect can design the extension with you after considering construction, planning and other restrictions.

Planning issues

Very often single storey rear extensions do not need planning permission being dealt with under permitted development, it is unlikely however that a two storey extension would be allowed the full width of the back of the house and planning permission would have to be sought.

Side Extensions


Design considerations

Single storey and two storey side extensions are a popular way of gaining more ground floor living space, whilst using up the usually wasted side return of the garden.

One of the most common problems is that a full side extension will often result in blocking the access to light for the door/window that exists at the rear part of the elevation. There is a number of things that could be done about this and a common approach is to allow for rooflights to the new side roof; the further back the rooflights are the better. This way natural light can reach deeper in the floor plan and help to define a new dinning or kitchen area at the rear of the house or flat.

Another common solution is to actually not build up to the rear door/window; this gives the opportunity for a nice, “external room”, landscaped courtyard between the existing house and the new side extension.

Planning Issues

Single storey extensions will normally be allowed right up to the boundary and the full depth of the existing house. However, unless the side flank of a two storey side extension is more that 2 meters from the boundary permitted development will not apply and planning permission will have to be sought.

Internal works and alterations



Not extending and adding space internally is often a cost effective solution, it generally possible to find unknown unused space and rearrange a layout to make it work much more efficiently.

Design considerations – Overlapping living spaces

Today our lives and what we want from our homes have become multi-dimensional our routines overlapping. We may be cooking while watching over a child’s homework, searching the internet or watching TV. Certainly Victorian and even more modern homes were designed with a much stricter division of activity in separate rooms.

While people generally do not like fully open plan they are prepared to relax traditional room division introducing the concept of activity zoning and soft spaces such as an open plan kitchen and making the most of circulation spaces. Such solutions should serve several purposes, such as the landing that allows the staircase to be set less steeply, while creating greater storage beneath.

Other things people now looking for are dedicated home office work space, providing new storage and ancillary space, clever rearrangement of the upper floors to create new bedrooms, bathrooms and wet rooms, particularly when the need for a new nursery or a cleaver solution to create a granny flat for an elderly or disabled relation give them independent living space.

It is also often possible to bring light and openness into family spaces with the introduction of roof lights or double storeys either into a basement or opening up into a loft that is unsuitable for conversion. The use of fold back glass doors in an open plan kitchen will flood the room with light.

Planning Issues

Internal refurbishment does not generally require planning permission

Building Regulation Issues

In terms of Building Regulations fire and means of escape are fundamental considerations however as long as account is taken of these from the outset of the design a solution is generally possible.

Cost of internal work

Conversion resulting in the removal of structural elements to create say an open plan kitchen does not need to be expensive and the use of fold back glass doors will flood the room with light.