L-shaped extensions: is one right for your house?

When an L shape makes sense

It suits houses with unused side space and a garden deep enough to extend into. It also suits people who want distinct zones, such as kitchen in one arm and dining or living in the other, without walls between them.

If you only need a bigger kitchen, a straightforward rear extension may be simpler and quicker.

The corner is the hard part

Where the two arms meet, the roof must turn a corner. With pitched roofs that means valleys; with flat roofs it means careful falls and drainage. Inside, the corner often needs a steel or post to carry the loads from both directions and from the existing house.

• Valley or flat roof junction at the corner
• Beams bearing from two directions
• Glazing positions that do not clash with structure

Structure and opening up

Both the side and rear walls of the existing house may be opened, requiring engineer designed beams and supports. Keeping a short section of original wall can simplify structure and help define spaces.

Planning considerations

Because it combines side and rear extensions, an L-shaped extension often falls outside permitted development and needs a householder application. Its impact on neighbours on both sides is considered.

Light and layout

An L shape offers two outside walls for glazing, so light can reach deep into the plan. Rooflights over the inside corner stop it becoming dark. Plan kitchen runs and dining areas so that the room works as a whole rather than as two corridors.

Budgeting for complexity

Because an L shape has more corners, roof junctions and structure than a simple rectangle, expect it to cost more per square metre than a basic rear extension. A fixed-price written quote based on proper drawings is the best way to compare it fairly with simpler options.

Heating and comfort in a large room

An L-shaped room with lots of glass can be hard to heat evenly. Underfloor heating suits it well, because it spreads warmth across the whole floor and keeps walls free for units and furniture. Good glazing specification and insulation matter even more than in a smaller extension.

Think about ventilation and shading too. Opening rooflights help release warm air in summer, and roof overhangs can reduce glare on the sunniest side.

Build sequence

Foundations for both arms are usually dug together, then walls and the corner structure go up before the roof. The existing walls of the house are opened once the new shell is weathertight, keeping disruption to the rooms inside as short as possible.

Because there are more junctions than in a simple rectangle, the roof and flashings at the corner and where each arm meets the house deserve extra attention during inspection.

Using both arms well

Give each arm a clear job: cooking in one, dining or sitting in the other, with the corner as the link. Avoid putting the main walkway through the middle of the kitchen, and position doors to the garden where they will actually be used, usually off the dining or sitting arm.

Deciding

Compare an L shape with a rear extension or side return on the same house. Look at usable floor area, how the spaces connect, light and complexity. A good designer can sketch options quickly.

We provide a free site visit to talk through the options, and with over 40 years of experience in carpentry and building we can advise on what is buildable. You receive a fixed-price written quote before work starts.

Common questions