How to Plan a House Extension in London on a Budget

A house extension in London is a significant investment, but there are smart ways to manage costs without compromising on quality. This guide explains how to plan and budget for a house extension in London, with practical tips to get the most value from your spend.

How to Plan a House Extension in London on a Budget

Understand What Drives Cost House Extension Budget London

The biggest cost factors for a house extension are size (square metreage), structural complexity (steelwork, underpinning, load-bearing wall removal), specification (standard vs premium materials and finishes), glazing (bi-fold doors, skylights, roof lanterns), and location (access constraints, conservation areas, London borough-specific requirements). Understanding these factors helps you make informed decisions about where to invest and where to economise.

Start with the Right Type of Extension

Some extension types offer better value than others. A side return extension (£35,000 to £55,000) is one of the most cost-effective options for terraced houses because it uses a narrow strip of land you are not currently using. A standard 3-metre rear extension (£35,000 to £50,000) is the most affordable way to add significant living space. A wraparound (£60,000 to £100,000) costs more but creates the most space per pound spent on terraced properties.

Choose Design and Build

Using a design and build company saves money compared to hiring an architect, structural engineer and builder separately. You avoid duplication of fees, gaps between stages, and communication problems. A single company manages the entire project efficiently. LCCL Construction offers full design and build from £35,000.

Prioritise What Matters Most

Invest in the structural envelope — good foundations, steelwork, roofing and weatherproofing. These are expensive to fix later. Economise on finishes that can be upgraded over time — kitchen units, bathroom fittings, flooring and decoration can all be improved later without structural work.

Do Not Cut Corners on These

Never cut costs on structural work, insulation, waterproofing, electrical work or plumbing. Poor quality work in these areas leads to expensive problems later and can affect your property value and ability to sell.

Get Multiple Quotes

Get at least two to three detailed quotes from reputable companies. Compare like for like — check what is included and excluded in each quote. The cheapest quote is not always the best value. Look for transparent pricing with no hidden costs.

Use Permitted Development

If your extension falls under permitted development rights, you save the cost and time of a full planning application. Most single-storey rear extensions up to 3 metres (terraced/semi-detached) or 4 metres (detached) qualify.

Consider Phasing the Work

If budget is tight, consider phasing the project. Build the extension shell and complete the structural work now, then finish to a basic standard and upgrade finishes later when budget allows.

Get a free consultation and instant quote from LCCL Construction. Call 020 8037 7332 or visit lcclconstruction.co.uk.