House Extension & Alterations Guidance Advice

Adding an extension to your house is obviously dependent on whether or not you have the available land adjacent to your property. If it is available an extension may be a more viable option compared to moving house, especially in areas where the difference in price of a house compared to the next size up is a daunting prospect. But you have the advantage that you don't need to move, and therefore, you are not dependent on selling your property and finding a new one that suits your needs - both within a time limit.

The costs involved can add up as with moving house. You will have the initial costs of using a architect to draw up the plans and submit them to the council for planning permission and building regulations approval.

And, of course, the council require a fee - in fact two fees - one for planning permission and one for building regulations approval. The fees for the building are, in general, going to be the largest outgoing, though you must remember that there may be additional costs depending on the type of extension you are planning. For example, if you are extending a room by knocking down an outside wall, you will have to pay a structural engineer to calculate the size of the RSJ (the beam that supports the wall above the new gap), and a quantity surveyor to calculate the cost of the bean. Sometimes, plans have to change after work has started and this may involve extra costs.

Extensions are a common form of development and help shape the local environment. Extending your home is a major investment that will often have an impact on your neighbours. Further, a badly designed extension could reduce the desirability of your property, affect your neighbours and reduce the quality of the environment.

Objective - to help you design your extension to achieve the highest design standards, even when planning permission is not required. This guide is designed to:

  • advise those seeking to extend a property
  • ensure consistency from decision-makers; and assist neighbours to understand the potential impacts of proposals.advise those seeking to extend a property
  • ensure consistency from decision-makers; and assist neighbours to understand the potential impacts of proposals.


These or other restrictions on your property’s title or conditions in a lease may require you to get someone else’s agreement before carrying out any building work. This may be the case even if you do not need planning permission. You can check this yourself or take legal advice.

Specialist Advice

Is your home subject to a special designation? For example if your home is within a Conservation Area or the indicative 1 in 100 year flood plain you may have to take specialist advice.

Listed Buildings

As well as planning permission you will need separate listed building consent. There is no fee to pay for this type of application.


Are there any trees nearby? Remember tree roots can go beyond a tree’s canopy, which means you could affect your neighbour’s trees. If a tree is protected by a Tree Preservation Order or is within a Conservation Area, you will need the Council’s consent to prune or fell it. You should take specialist advice in these circumstances. There is no fee to pay for this type of application.


Put yourself in their shoes. Would you be concerned about the extension you want to build being next to you? If yes then perhaps you need to think again. Your neighbours rights to light See separate guideline advice on this.


Speak to your neighbours. How would you feel if the first thing you knew about your neighbour intending to start building works is either a letter from the Council or the builders turning up to start work? Disputes often arise because of a lack of communication or misunderstanding.


How will the extension appear from your neighbour’s point of view? Is the ground level ? Is there a direct or indirect loss of car parking spaces? Does the size of your plot reduce the scope for extending? Could you make your home more environmentally friendly and implement ‘green’ changes? Are you going to change the boiler or use a water butt? Consider drainage and flood risk, for example reducing the amount of hard surfaced area.