Ground conditions & foundations
Clay soils, nearby trees and old drains can mean deeper or specially designed foundations. Trial holes and an engineer’s design settle this early.
Get a quote for ground conditions & foundations
Extension budgets explained, London-wide
What Will Your London Extension Cost?
Online price-per-square-metre figures rarely survive contact with a real house. We explain the things that actually move the number, then price your extension line by line.
- Line-by-line pricing
- Measured on site, not guessed
- Insurance certificates on request
- Price visits across all London boroughs
What moves the number
The biggest drivers of extension cost
Size matters, but it is rarely the whole story. These are the items that usually make two similar-looking extensions cost very different amounts.
Steelwork & structural openings
Knocking through the back wall usually needs steel beams and padstones. Wide, clear openings with no posts need larger sections and more engineering.
Get a quote for steelwork & structural openingsGlazing, roof lights & doors
Large sliding or bifold doors and roof lanterns are often among the most expensive single items. Specification and size make a big difference.
Get a quote for glazing, roof lights & doorsRoof type
A simple flat roof generally costs less than a pitched or vaulted roof with tiles, but insulation and drainage still need to meet Building Regulations.
Get a quote for roof typeKitchens, floors & finishes
The kitchen, flooring and underfloor heating can rival the cost of the shell itself. We price them separately so you can see where the money goes.
Get a quote for kitchens, floors & finishesFees & approvals
Drawings, structural calculations, Building Control, and where needed a party wall surveyor and planning application all sit alongside the build price.
Get a quote for fees & approvals
Honest numbers
Why we don’t publish a price per square metre
A single rate hides the things that matter: access through a terraced house, the depth of the foundations, the size of the glazing and the quality of the kitchen. We would rather visit, measure and give you a figure that is built from your own project.
- Every line of the quote is explained
- Provisional sums are clearly labelled
- Options shown so you can trim the budget
From idea to figure
How we get to your number
Four steps that turn a rough idea into a price you can plan around.
Tell us the idea
Use the form to describe the extension, even roughly. Photos of the back of the house help.
Site visit
We measure, check access and drainage, and talk through the options that most affect cost.
Itemised quote
You receive a written breakdown with each stage priced, plus any provisional sums explained.
Refine the scope
We help you adjust glazing, finishes or layout if the first figure is higher than you hoped.
Why this approach
Pricing you can actually compare
A clear breakdown makes it easier to compare builders and to make decisions.
Like-for-like comparisons
Separate lines for each stage let you compare our quote with others properly.
Real measurements
Figures are based on your house, not an average of other people’s projects.
Straight answers on savings
We will tell you which changes save real money and which barely move the total.
Programme alongside price
You see how long each stage is likely to take, as well as what it costs.
Living through the build
We explain what disruption to expect and how the kitchen move will be handled.
Insurance details on request
Ask for our insurance certificates alongside your itemised quote and we’ll send copies before a start date is agreed.
FAQ
Extension cost questions
Common questions from homeowners trying to set a realistic budget.
Can you give me a price per square metre?
We prefer not to, because a single rate tends to mislead. Two extensions of the same size can differ widely in cost depending on foundations, glazing, roof and finishes. A site visit gives a far more reliable figure.
What usually costs more than people expect?
Foundations on difficult ground, steelwork for wide openings, large glazed doors and the new kitchen are the items that most often surprise people. Moving drains can also add cost.
Are design and approval fees included?
Our quote separates the build from fees such as drawings, structural calculations, Building Control and party wall costs, so you can see each one clearly.
Do I need planning permission?
Some single-storey rear extensions fall under permitted development, others need full planning permission, and conservation areas have stricter rules. Your council or the government’s Planning Portal can confirm what applies to your house.
What is a provisional sum?
It is an allowance for something that cannot be priced exactly yet, such as foundations before the ground is dug. We label these clearly and explain how the final figure is worked out.
How can I reduce the cost?
Simplifying the roof, choosing standard-size glazing, keeping drainage where it is and phasing finishes are common ways to bring a budget down. We can show the effect of each option.
How long is a quote valid?
Material prices change, so each quote states how long it is valid for. If your start date moves, we can review it.
Is the quote free?
Yes. The site visit and written quote are free and there is no obligation to go ahead.
Are you insured?
Yes, ask for our insurance certificates when you receive your quote and we’ll send copies before a start date is agreed. Checking cover is sensible with any builder.
Areas served
Extension pricing across London
We visit homes in every London borough to measure up and price extensions.
Costs are shaped by things that vary across the capital, such as access for materials, parking and skip permits, and how much space there is around the house.
Whichever borough you live in, the quote is built from a visit to your property.
Boroughs we visit
- Barking and Dagenham
- Barnet
- Bexley
- Brent
- Bromley
- Camden
- City of London
- Croydon
- Ealing
- Enfield
- Greenwich
- Hackney
- Hammersmith and Fulham
- Haringey
- Harrow
- Havering
- Hillingdon
- Hounslow
- Islington
- Kensington and Chelsea
- Kingston upon Thames
- Lambeth
- Lewisham
- Merton
- Newham
- Redbridge
- Richmond upon Thames
- Southwark
- Sutton
- Tower Hamlets
- Waltham Forest
- Wandsworth
- Westminster
Free quote
Get an itemised extension quote
Describe the extension you have in mind and we’ll arrange a visit to measure and price it.
Swap guesswork for a real figure
Book a free visit and get a line-by-line price for your extension.