What is a single-storey extension?

The short definition

A single-storey extension is any addition to a house that is one floor high. It sits on its own new foundations, ties into the existing walls and is roofed either flat, with a lean-to pitch, or with a pitched roof and gable. Inside, it normally opens into an existing room so the two spaces work as one.

People use the phrase for everything from a small utility room to a full-width kitchen and family room. The label says nothing about size; it only tells you the height, which matters because height is one of the things that decides whether a project needs a full planning application.

Rear extensions

The rear extension is the most common type. It projects out into the back garden from the back wall of the house, usually across part or all of the width. On semis and terraces it is the obvious way to turn a narrow galley kitchen into a room you can eat in.

The things that shape a rear extension are how far it projects, how close it comes to the neighbour's boundary, and how its roof meets the existing wall under the first-floor windows. A lean-to roof is simple and cheap to detail; a flat roof with rooflights gives a cleaner ceiling and more headroom at the far end.

Side-return extensions

Many Victorian and Edwardian terraces have a narrow alley down the side of the rear wing. A side-return extension fills that gap, widening the kitchen by a metre or two. The gain looks small on a drawing, but it often changes a corridor-shaped room into one that takes a proper table.

Because a side return sits right on or near the boundary, a party wall notice is usually needed, and the new wall has to be built carefully so it does not undermine the neighbour's foundations or block their light.

Wrap-around extensions

A wrap-around combines a rear and a side-return extension in an L shape. It gives the biggest single-storey gain on a terraced or semi-detached house and is usually the point where the whole ground floor is re-planned rather than one room enlarged.

Wrap-arounds nearly always need structural steelwork to take out the old rear and side walls. That makes the design and Building Regulations stage more involved, and it is worth getting the layout settled before anyone prices it.

Front and garage-side extensions

Less common but useful are small front additions, such as a porch that grows into a cloakroom, and side extensions on detached houses, sometimes built in front of or beside an existing garage. Front work is more visible from the street, so the planning rules are tighter and the brick match matters more.

What to decide before you ask for quotes

Decide what the new space is for, how you will use it day to day, and which walls you are happy to lose. Measure the garden and note drains, manholes, trees and any change in level, because all of these affect the foundations. Then look at the roof: whether you want rooflights, a lantern or a pitched ceiling changes the build more than most people expect.

With that brief, a builder can tell you quickly whether you are looking at permitted development or a planning application, and whether the job is straightforward masonry or needs an engineer's steel design.

How we approach them

We are a Dunstable-based firm with more than 26 years on residential building work, and family extensions are a large part of what we do. Our bricklaying is NVQ Level 2 qualified, we are members of the Federation of Master Builders and fully insured. We build the foundations, the brick-and-block shell, the roof and the opening into the house, and we work to the approved drawings and the Building Control inspector's checks.

If you are still at the idea stage, the cost calculator on this site gives a rough starting point, and a free written quote follows a site visit.

Questions people ask