House Extensions
House extensions designed and built to last.
Single-storey, double-storey, side return, wrap-around and rear extensions across London. Full planning, structural and build coordination under one principal contractor.
Expert house extension contractors in London.
A well-designed and properly built house extension adds genuine value to your home — but only if the structural work is sound, the planning is correct and the execution is professional.
RCB manages the full extension process. From assessing planning requirements and commissioning structural calculations through to full construction management, Building Control inspections and final handover.
Whether you are adding a rear extension to open up your kitchen, a side return to reconfigure your ground floor, or a double-storey extension to add bedrooms and living space, RCB brings the experience and accountability to deliver it properly.
What's included
How It Works
The RCB process for this service.
Feasibility Review
We assess your property, your planning options and the structural requirements of your proposed extension.
Design & Approval
Architectural drawings, planning application or permitted development assessment, structural calculations and Building Regulations submission.
Estimate & Contract
A detailed, itemised estimate covering every element of the extension. No lump sums — clear scope and clear costs.
Build & Complete
RCB manages groundworks, structure, roof, external envelope, internal fit-out and handover with Building Control sign-off.
Planning & Regulations
House extensions may fall within Permitted Development rights and not require planning permission — or may require a full planning application depending on size, location, and your local authority. Building Regulations approval is always required. Structural calculations are required for most extensions. Party wall matters may apply if your property is attached. RCB coordinates all of this.
FAQs
Common questions.
Do I need planning permission for a rear extension?
Many single-storey rear extensions up to 4 metres (3 metres for terraced and semi-detached) fall under Permitted Development and do not require a planning application, subject to conditions. Larger extensions or those in conservation areas require full planning permission. RCB will assess your specific situation.
How long does a house extension take?
A typical single-storey rear extension takes 10–16 weeks from site start to completion. Double-storey extensions typically take 16–24 weeks. Pre-construction (design, planning, Building Regulations) adds 8–20 weeks depending on complexity and planning authority speed.
What will a house extension cost?
Costs vary significantly by size, specification and location. As a guide, single-storey extensions typically start from £30,000–£50,000 depending on size and finish. RCB provides a fully itemised estimate once we understand your project.
Will I need to move out during the extension?
In most cases, no. The majority of extension works allow you to remain in your home, though there will be periods of disruption — particularly during structural work and when internal connections are made.
What is a party wall agreement and do I need one?
If your property shares a wall with a neighbour, you may need to serve a Party Wall Notice before certain types of work. This is a legal requirement, not optional. RCB will advise on this and can help coordinate the process.
Related services:
Ready to discuss your project?
Book a free project review or send your drawings for a detailed estimate.