How Much Does a House Extension Cost in 2026? A Wirral & Chester Guide

Extension cost is the question every homeowner asks first, and the honest answer is: it depends on far more than square footage. Here’s a realistic breakdown based on the kind of projects we build across the Wirral and Cheshire.

What drives the price

• Structural complexity — a single-storey rear extension is cheaper per square metre than a double-storey extension or one involving steel beams to open up the existing house.
• Glazing — bi-fold or sliding door runs, roof lanterns and large expanses of glass cost significantly more than a standard window, but they’re usually what makes an extension feel special.
• Ground conditions — unexpected issues like running sand, old drains or poor soil (which we’ve hit on Wirral projects before) can add cost that no fixed quote could have predicted.
• Specification — kitchen, flooring and fittings vary enormously in price, and it’s common for the “extension” budget and the “fit-out” budget to be roughly similar in size.
• Listed building or conservation area status — sympathetic materials and a longer planning process both add cost and time.

Our sweet spot

Most of the projects we take on sit between £100,000 and £500,000, typically combining an extension with some refurbishment of the existing house — because once you’ve extended, it rarely makes sense to leave the rest of the property untouched and mismatched.

Why we quote the way we do

On several projects, we’ve used our in-house quantity surveyor to establish a firm build cost before a single detailed architectural drawing is produced. That means the design is shaped around a budget you’ve already agreed to, rather than a design being drawn first and the cost only becoming clear once it’s too late to change course without wasted fees.

It’s also why we offer a full turnkey design-and-build service rather than just quoting on someone else’s drawings — when the same team designs, builds and finishes a project, cost surprises are far less common because nothing gets lost in translation between an architect, a quantity surveyor and a builder who’ve never actually spoken to each other.

If you want a realistic figure for your own project rather than a rule of thumb, the fastest way is a site visit — get in touch and we’ll talk it through.