More space, beautifully gained.

Rear, side return and wrap-around extensions designed around how you live — planned, drawn and detailed from first sketch to building regulations approval.

Start your extension ↗

Contemporary rear extension to a North London Victorian terrace

Extension design

Light, proportion and flow decide whether an extension works.

The best extensions don't look added on. We design around daylight, ceiling heights and the connection to the garden, so the new space improves the whole house — and adds measurable value to the property.

Feasibility & brief

We assess the house, planning constraints and your budget, then agree a realistic brief.

Design & planning

Concept to detailed design, with the planning application or lawful development certificate handled for you.

Technical design

Building regulations drawings, structural calculations and support while your builder is on site.

A finished Simplicity Designs project in London

“The best extension is the one that feels like it was always part of the house.”
Hakki HassanFounder & Principal Designer

Do I need planning permission for an extension?

Many single-storey rear extensions fall within permitted development — generally up to 3m from the original rear wall (4m for a detached house), or 6m and 8m under the prior approval route. Conservation areas, Article 4 directions, flats and listed buildings have tighter or no rights. We confirm which route applies to your address before design begins.

Which type of extension suits your house?

A rear extension opens the back of the house to the garden; a side return fills the narrow alley typical of Victorian and Edwardian terraces; a wrap-around combines both for the largest gain; and a double-storey extension adds bedrooms above at far less cost per square metre than moving. We test the options against your budget and the council's guidance.

How much does an extension cost in London?

As a guide, single-storey extensions in London typically run from £2,200 to £3,300 per square metre depending on specification and structure. We design to your budget from the outset and advise where the money makes the most difference — glazing, structure and the junction between old and new.

Structure, party wall and building control

Open-plan extensions rely on steel beams, and work near a boundary usually engages the Party Wall Act. Because our structural engineering and party wall work is handled in-house, beams, notices and building control queries are resolved by the same team that drew the design.

See structural engineering services →