It will make your home more spacious, more easily sellable and possibly even more beautiful. An extension is one of the most valuable improvements you can make to your property, so long as you do it properly, accurately—and legally.

‘The most common mistakes people make when building an extension are doing the work without getting planning permission from the local council; thinking that the extension qualifies for permitted development rights when it doesn’t; and building something which aesthetically doesn’t work with the overall look and feel of the rest of the building,’ says Camilla Dell of Black Brick Property Solutions.

However, she adds, the good news is that these mistakes can easily be avoided by doing some thorough research in advance.

The first and most crucial step to take after you decide to build an extension is to get the planning right. New regulations that came into force in October 2008 classify extensions as permitted development work. This, together with the fact that a new wing can add value or speed up the process of selling your property in the future, has conspired to make extensions particularly mouth-watering.

What people don’t know, however, is that the permitted development rule only applies if more than a dozen conditions are met. Among others, the new wing, together with other buildings, should not take up more than half the land around the original house; it shouldn’t be higher than the highest part of the room; and it should have no verandahs, balconies or raised platforms.

So far, so simple, but some other limitations get really technical and can be confusing for the layman—for example, the one that sets the maximum depth of a single storey rear extension to ‘three metres beyond the rear wall of an attached house and four metres beyond the rear wall of a detached house.’ Or the one that requires side extensions to be ‘single storey with a maximum height of four metres and width no more than half that of the original house’.

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And of course, ‘even if you think your home may qualify within the new ‘permitted’ development rules, if you live in a conservation area, or your home is listed, you will still need to obtain planning consent and permission in order to carry out an extension,’ says Ms Dell (the full list of constraints is available on the Planning Portal’s website at www.planningportal.gov.uk/england/genpub/en/1115315206517.html).

For this reason, both Ms Dell and Alan Waxman of boutique property developer Landmass London highly recommend hiring an experienced architect to avoid any potential planning hurdle. Ms Dell in particular suggests choosing one with good contacts within the council, who ‘should be able to assist you with everything from planning consent to building regulation.’

Of course, an architect is also invaluable in making the most of your extension’s space, light and layout, and in developing the right aesthetics for it.

Owners of period properties are often torn between building a new wing that seamlessly integrates with their existing home or going for an eye-catching contrast with a thoroughly contemporary style. No solution is necessarily the best one—though the second is by far riskier—and each needs to be carefully pondered as mistakes can turn out to be costly. Not only will you dislike a ‘wrong’ extension but it is likely to shave the pounds off your asking price if you ever resell your house.

To make the best possible choice, says Mr Waxman, ‘don’t use the first architect you come across, but get proposals from three different ones.’ This will allow you to choose the most convincing one—and you will get plenty of free advice to boot.

To help you in your selection, show the architects’ drawings to good local estate agents. ‘You want to get bang for your buck,’ says Mr Waxman, and getting professional feedback from market experts will help you do that. By contrast, he urges, don’t consult your friends. ‘They’ll drive you nuts,’ he says bluntly.
Once you have a project and permission to carry it out (or once you have ascertained you need no permission), it is time to get the builders in. With your architect’s help, get quotes from different builders, finalise your budget and consider how best to fund the expense—Mr Waxman believes that the cheapest way to finance your extension is to get it on your mortgage.

Above all, avoid the mistake of doing too much by yourself in the naïve hope that it will save you money because ‘it will cost you more in the long run,’ according to Mr Waxman. Instead, choose a reputable contractor, insist on an enforceable contract with penalties built in for delays or problems with the work, and ask your architect or a project manager to manage the building process. They will be able to ensure the work is carried out as swiftly and accurately as possible, and they’ll uphold quality standards for you. ‘Do not try and manage the project yourself,’ warns Mr Waxman. ‘It will end in tears!’

If all this sounds too daunting, there is always another option. Get planning permission for an extension, then find yourself another property to buy and sell your existing house and the consent that goes with it. Like that, says Mr Waxman, ‘you can sell it with the benefit of planning, which will give you some uplift in price.’

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