The hidden costs of an extension

8 min read

Planning a thorough budget at the start of your project can help you avoid nasty surprises and unexpected costs later on, advises Rebecca Foster

IMAGE: GEORGE AND JAMES ARCHITECTS/MEGAN TAYLOR

When you’re thinking about adding space to your existing home, it’s easy to get caught up in the excitement of the early design phase as you visualise knocking down walls, creating bright, open spaces and kitting them out with high-spec fixtures and fittings. However, before getting

TRICKY TASK This 1980s house was built using a timber frame, so structural alterations were more complex than with a masonry build. carried away by fantasies of your dream, top-of-the-range kitchen and coordinating accessories, it’s important to plan a comprehensive budget that covers all aspects of your scheme.

Of course, construction costs and the sum you pay for new furniture will take up a significant portion of your project fund — but the outgoings won’t end there. There are various other costs you’ll need to factor in from the start of your project to avoid nasty surprises and spiralling costs later on. For instance, the cost of submitting a planning application and any associated surveys you need to conduct as part of your submission should be included in your calculations, as should the professional fees of your designer, engineer and any other specialists you need to bring on board. You may also need to factor in additional structural work to the existing building, landscaping works, and upgrades to your home’s heating and electrics, to name a few. To help you avoid the pitfalls associated with unexpected costs, we’ve outlined some of the key areas you’ll need to budget for when building an extension.

LIGHT TOUCH Cox Architects designed this rear extension to a large Victorian house in a south London conservation area. In addition to the extension itself, a sleek new grey sandstone patio was built as part of the works.
IMAGE: ASBJOERN SCHMIDT

1 PLANNING FEES

If your extension requires consent from the local council, don’t forget to account for the cost of the planning application itself — as well as the cost of paying a professional architect or designer to put together drawings (more on this later). A householder planning permission application for an extension to a single dwelling costs £206 — though planning permission might not be required if your project is covered by Permitted Development rights. Even in the latter scenario, it’s often worth obtaining a Lawful Development Certificate for peace of mind. Fees for proposed works are typically half the cost of a full planning application — in England they’re £103, £85 in Wales and £101 in Scotland. However, if you’ve already gone through the construction process and are applying for the certificate