How to create the perfect extension: adding a modern glass box to a listed Georgian house in an East London conservation area

East London has many streets of small, and often dark, Georgian and Victorian terrace houses. HÛT architects were asked to extend such a house in a conservation area near Mile End.

The Georgian property already had a badly built Eighties extension tacked on to the back — half of which was double height and the other half single height, both sides with pitched slate roofs, extending less than four metres.

The taller side held a bathroom on the upper floor, with storage space beneath accessed from the garden, and the two sides did not connect internally. The owners wanted to replace the inefficient addition for a space across the width of the house.

HÛT considered permitted development, but with a listed house — or one in a conservation area — a two-storey extension is not allowed, so HÛT went via the planners.

“We got a dialogue going straight away,” says Rachael Davidson of HÛT. “This is important, as planners can be very helpful. In this case, we were not allowed to change the existing staircase, so our design evolved around that. Plus, we had to retain a lot of historic fabric.

“Before the planning application, we presented the owners with lots of options. We submitted a design that used traditional brick for the two-storey side, and a modern glass box, single storey, for the other. The two sides connect inside, making a very usable space. The planners liked that we retained a lot of traditional brick in the design.”

The new extension, which has a blueprint that is almost the same as the original, replaces two useless spaces with a larger family friendly area for dining and living, full of light from the glass box, and containing two extra bathrooms. It looks terrific.

The total cost came to £350,000.

BUDGET FOR THE EXTRAS

There are many things to consider that might bump up the fees. Factor in structural engineers, planners, building regulations and inspectors’ visits, plus party wall agreements that grow if your neighbour opts to have their own party wall surveyor.

HÛT’s Davidson explains that, while all jobs are different, total fees are usually about 20 per cent. In a smaller job, the fees may be a larger proportion of the whole cost.

Consider about 10 per cent for the architect and 10 per cent for all the other fees as a good starting point.

John Norman, of Mustard Architects, says: “Budget at least £700 to £1,000 for a structural engineer, and about £900 for building regulations. You can get planning application fees at the local planning office. If the plans are thrown out because of objections, then you have to redraw, and re-submit, which means more fees.