How Long Does a House Extension Take to Build in London?
Updated: Nov 2
A house extension in London typically takes between 10 and 24 weeks to build, depending on the size and complexity of the project. A single-storey rear extension usually takes 10 to 16 weeks, a side return extension takes 8 to 14 weeks, and a double-storey extension takes 14 to 24 weeks. The full project timeline including design and planning stages is usually 6 to 12 months from start to finish.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — we look up the conservation areas, Article 4 directions and listed buildings for you, and you see which parts are permitted development and the from-price for each. Lawful Development Certificate included on every permitted development job.
The Full House Extension Timeline
How Long Does a House Extension Take to Build in London. The construction phase is only one part of the overall timeline. Here is a typical breakdown of the complete process:
Stage 1 — Consultation and Survey (1 to 2 weeks): Initial consultation to discuss your requirements, followed by a measured survey of your existing property.
Stage 2 — Architectural Design (2 to 4 weeks): Production of planning drawings showing the proposed extension design, floor plans, elevations and site layout.
Stage 3 — Planning Permission (6 to 10 weeks): If required, a planning application is submitted to your local council. Most councils aim to determine applications within 8 weeks.
Stage 4 — Building Regulations Drawings (2 to 3 weeks): Detailed technical drawings showing exactly how the extension will be constructed, including structural calculations.
Stage 5 — Party Wall Agreements (2 to 8 weeks): If your extension is near a boundary with a neighbour, party wall notices must be served. The process takes a minimum of two weeks if your neighbour agrees, but can take longer if a surveyor is appointed.
Stage 6 — Construction (10 to 24 weeks): The actual building work, from foundations through to completion and finishing.
How Long Does a House Extension Take to Build in London, What Affects the Build Time?
Several factors can affect how long your house extension takes to build. The size of the extension is the most obvious factor, but other things that influence the timeline include the complexity of the foundations, weather conditions during construction, the availability of materials and trades, the level of internal finishing required, and any unexpected issues discovered during construction such as hidden drainage or structural problems.
How to Speed Up the Process
Choosing a design and build company like LCCL Construction can significantly speed up the process. Because we handle all stages under one contract — from architectural design and planning through to construction — there are no gaps between stages and no coordination issues between separate architects, engineers and builders.
About LCCL Construction
Can it be done under permitted development?
A single-storey rear extension of 3 m on a terrace or semi (4 m on a detached house), a side-return infill and a side extension up to half the original width are permitted development on a house outside a conservation area or Article 4 street — no planning application, just a Lawful Development Certificate, which we apply for on every one. Fixed-price permitted development extensions start from £42,000 inc. VAT (£35,000 + VAT) at economy specification, design and build inclusive, and the 6 m / 8 m larger home extension goes through a 42-day prior approval notification rather than a full application. See our permitted development projects page for every product with its from-price and the checks we run before we confirm a project qualifies.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — we look up the conservation areas, Article 4 directions and listed buildings for you, and you see which parts are permitted development and the from-price for each. Lawful Development Certificate included on every permitted development job.
LCCL Construction is a design and build company based in Finchley, London N3, specialising in loft conversions and house extensions across London and Hertfordshire. With over 20 years of experience and a 4.7-star rating out of 5 stars rating on Trustpilot, Reviews io, Yell, LCCL Construction Reviews from 200 reviews, we handle everything from architectural design and planning permission through to construction and finishing. Contact us on 020 8037 7332 or visit lcclconstruction.co.uk for a free consultation and instant quote.
%2C%20founder%20of%20LCCL%20Construction.jpeg)
