Gain living space downstairs and a bedroom or bathroom upstairs in a single project. A coordinated architecture, structural engineering and build team delivers double-storey (two-storey) extensions across North West London.
A double-storey (two-storey) extension adds space on both the ground and first floors at the same time — typically a larger kitchen or living room below and an extra bedroom or bathroom above. Built to the rear or the side, it is one of the most cost-efficient ways to add significant space because the foundations, roof and scaffolding serve two floors at once. It is also one of the most planning-sensitive extension types, so design and policy expertise matter.
The first-floor level typically delivers a new bedroom, en-suite or family bathroom — the space that adds the most to how a family uses a home.
Because one set of foundations, roof and scaffold serves two floors, a double-storey extension usually delivers a lower cost per square metre than two separate single-storey projects.
Two-storey extensions rarely fall within Permitted Development in practice and usually require a full householder planning application; conservation areas add further controls.
Two-storey rear extensions must respect daylight/overlooking tests — generally not projecting more than 3m, staying at least 7m from the rear boundary, and matching the existing roof pitch and materials.
Carrying two floors means more substantial foundations, beams and connections. The structural design and certification requirements are coordinated before construction.
Two-storey work close to a boundary almost always triggers the Party Wall etc. Act 1996. The required notices and surveying route are coordinated as part of the pre-construction plan.
A two-storey extension is a larger build than a single-storey addition. The figures below are indicative on-site durations; a project-specific programme follows the early review, while a fixed quotation requires sufficient design, specification and constraint information.
| Project Type | Indicative Timeline (on site) | Typical Scope |
|---|---|---|
| Two-storey side extension | 18–26 weeks | Two floors, structure, roof, glazing, finishes |
| Two-storey rear extension | 18–28 weeks | Ground + first floor to the rear |
| Double-storey + internal remodel | 24–34 weeks | Extension with wider reconfiguration |
| Premium specification | By programme | Bespoke joinery, en-suite, designer finishes |
Every project is priced individually. Use our cost calculator or book a free consultation to confirm the next scope and pricing step.
An architect assesses the side or rear, reviews the existing structure and roof, and discusses how the two new floors can work for your home and budget.
We design both floors with 3D visuals and submit a full householder planning application, designed around your council's daylight, overlooking and design policies.
The project structural engineer designs the upgraded foundations, beams and floor structure; we secure Building Regulations approval and manage inspections.
We serve party wall notices, then build foundations, two-storey structure, roof, glazing and finishes under a dedicated project manager.
We complete the new rooms — kitchen, bathroom, joinery, flooring and decoration — and hand over with the applicable completion certificates and agreed warranty documents.
A selection of comparable completed projects from our portfolio. Browse the full case study portfolio or book a consultation.
Book a free, no-obligation consultation. Our architects will assess what two floors of new space can deliver on your property, and explain the design, consent and pricing route for your property.
We deliver this service throughout our core North London territory. Explore the neighbourhoods we specialise in:
Local double-storey extensions guidance for each of our North London neighbourhoods: