If you’re starting to plan a home extension, the cost is usually the first question and the hardest one to answer honestly. Every builder’s website seems to promise a figure, but the truth is that a house extension is never a fixed price until your design is finished and signed off. What we can do is explain what actually drives that figure, so you go into the process with realistic expectations rather than a number pulled out of thin air.
Why We Don’t Give Ballpark Estimates
Most house extension enquiries start with the same question: “roughly how much?” It’s a fair thing to ask, but a genuine ballpark figure is close to useless. Two extensions of the same size, on two different houses, can cost very different amounts depending on the ground conditions, the existing structure, the finish specification and how the new space connects to the rest of the home.
At Stevens Design & Build, we would rather take the time to understand your project properly than hand you a number that turns out to be wrong once the real design work starts. That’s why our process always begins with a free consultation and a proper feasibility assessment before any figure is discussed.
What Actually Shapes the Cost
A few factors consistently make the biggest difference to what a house extension costs:
- Scope and footprint. A single storey extension is generally more straightforward and less expensive than a two-storey addition, simply because there’s less structure involved. But even within a single storey extension, a small rear extension and a full-width wraparound are very different projects.
- Structural complexity. Removing load-bearing walls, working around existing drainage, or building close to a boundary can all add cost that isn’t obvious from the outside.
- Specification. Two extensions with identical dimensions can end up worlds apart in price depending on the windows, doors, flooring and finishes chosen. This is where a full 3D visualisation earns its keep, because it lets you see and adjust the specification before it’s locked into a fixed price.
- Services and connections. Moving a kitchen, adding a bathroom, or tying new plumbing and electrics into an existing system all add complexity that varies from house to house.
Why Most Stevens Design & Build Projects Fall Between £60,000 and £150,000
As a general guide, most of our projects land somewhere between £60,000 and £150,000, though every proposal is priced individually once your design is finished. This range reflects the kind of work we typically take on, from a considered single storey extension through to a larger, more complex build. It isn’t a promise about what your specific project will cost, and we’d rather be upfront about that than quote a figure we can’t stand behind.
How We Get You to an Accurate Number
Every Stevens Design & Build house extension follows the same process, regardless of size:
- Free Consultation — We visit your home, listen to your brief and give you an honest view of what’s achievable.
- Feasibility — We assess layout, planning and structural considerations, so your budget expectations are grounded in reality early on.
- Design and Visualisation — Full 2D plans and 3D renders, so you see exactly what you’re getting before anything is priced.
- Fixed Proposal — A detailed, itemised price, agreed before work begins and never changed afterwards.
By the time you receive a fixed proposal, you’re looking at a genuine figure for your specific extension, not a generic estimate dressed up as one.
Thinking About a House Extension?
If you’re at the early stages of planning a house extension and want an honest conversation about what’s achievable, we’d be glad to talk it through. There’s no obligation, and no cost, for that first conversation.
