ROI of a Home Extension London 2026: What Return on Investment Can You Expect?

A home extension is one of the highest-return investments most London homeowners will ever make — but the ROI varies significantly by extension type, location and specification. Understanding the return you can expect before starting your project is critical to budgeting realistically and prioritising the right extension type for your property. This guide sets out the expected return on investment for each of the four main extension types, worked examples across different London locations, and the factors that push ROI up or down. LCCL Construction has delivered hundreds of extensions across London and Hertfordshire with 20+ years of value uplift data behind our numbers.

LCCL Construction — how to calculate ROI on your London home extension

What Is the Average ROI on a Home Extension in London?

On our projects and local sold prices, a well-planned project of this kind usually adds more to the value of the home than it costs to build — see our guide on how much value an extension adds. In premium London postcodes ROI can exceed 400 per cent. In outer London ROI is typically 150 to 200 per cent.

The key metrics: a £60,000 extension typically adds £90,000 to £180,000 in property value in outer London and £120,000 to £240,000 in inner London.

ROI by Extension Type in London 2026

Rear extension ROI: 150-250 per cent. A £66,000 inc. VAT (£55,000 + VAT) rear extension typically adds £85,000 to £140,000 in value. See full rear extension cost guide.

Side return extension ROI: 200-300 per cent — the highest per-pound return because you convert dead space into usable living space. A £55,000 side return typically adds £110,000 to £165,000. See full side return cost guide.

Wraparound extension ROI: 150-300 per cent. A £85,000 wraparound typically adds £130,000 to £255,000. See full wraparound cost guide.

Double storey extension ROI: 175-300 per cent — highest total value uplift because it adds bedrooms plus ground floor space. A £110,000 double storey typically adds £190,000 to £330,000. See full double storey cost guide.

Worked Example 1: Rear Extension in Outer London

Property: 3-bedroom Victorian terrace in Enfield EN1 valued at £575,000.

Extension: 18 sqm single storey rear kitchen extension.

Construction cost: £52,000.

New property value after extension: £695,000.

Value uplift: £120,000.

ROI: 231 per cent.

This is a typical outer London ROI on a rear extension.

Worked Example 2: Wraparound in Inner London

Property: 4-bedroom Victorian terrace in Islington N1 valued at £1,150,000.

Extension: 28 sqm wraparound extension with bifolds, roof lantern and premium finishes.

Construction cost: £95,000.

New property value after extension: £1,395,000.

Value uplift: £245,000.

ROI: 258 per cent.

Worked Example 3: Double Storey in Central London

Property: 4-bedroom Edwardian terrace in Kensington W8 valued at £2,850,000.

Extension: 32 sqm double storey rear adding master bedroom with ensuite.

Construction cost: £185,000.

New property value after extension: £3,450,000.

Value uplift: £600,000.

ROI: 324 per cent.

Factors That Push ROI Higher

Extensions that unlock a higher property class deliver the highest ROI — for example turning a 3-bedroom home into a 5-bedroom home crosses a price band and can add 25-40 per cent value on its own. Extensions that add bedrooms plus a bathroom deliver higher returns than extensions that only add ground floor space. Premium natural light features — bifold doors, roof lanterns, sliding glass — add disproportionate value. High-quality architectural design that opens up the ground floor into an integrated whole delivers higher value than a bolt-on extension.

Factors That Reduce ROI

Over-development beyond neighbourhood norms reduces ROI — extending a 3-bedroom terrace into a 7-bedroom house exceeds street market ceiling and returns diminish. Poor design that leaves the extension looking bolted on rather than integrated. Low-cost finishes that reduce perceived quality. Insufficient natural light making the extension feel dark. Extensions that eliminate too much garden — outer London buyers value gardens highly.

How to Calculate Your Extension ROI

Step 1: Get an accurate construction cost estimate. Use our home extension cost guide or the LCCL instant quote calculator. Step 2: Research current property value using local estate agent valuations, Zoopla and Rightmove sold prices. Step 3: Research post-extension property values by looking at similar-sized extended properties in your street or immediate area on sold-price databases. Step 4: Calculate value uplift as (new value) minus (current value). Step 5: Calculate ROI as (value uplift) divided by (construction cost) times 100.

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 a planning application? Check if you need planning permission

Frequently Asked Questions About Home Extension ROI in London

What is the highest ROI extension type in London?

Side return extensions typically deliver the highest per-pound return — 200-300 per cent — because they convert dead alley space into functional living space.

How long does it take to realise the ROI on an extension?

Value uplift is typically reflected in property valuation immediately upon completion. If selling, expect the higher price at the next valuation cycle 6-12 months after works finish.

Is a house extension a better investment than moving?

For most London homeowners yes. Stamp duty on trading up plus estate agent fees plus moving costs typically total £75,000 to £250,000+ on higher-value moves — a cost that generates zero value uplift. An extension of similar cost typically delivers 150-300 per cent value uplift.

See our full guide on how much value an extension adds.

To discuss your home extension project with an award-winning LABC 2024 design and build company call LCCL Construction on 020 8037 7332 or get an instant quote online.