Estimated reading time: 5 minutes
You type “how much does a rear extension cost in London” into Google.
A number comes back. Maybe a range. Maybe a neat price-per-square-metre figure that feels reassuring — concrete enough to build a budget around.
And that’s exactly where the trouble starts.
Online calculators and AI-generated estimates aren’t dishonest. They’re just incomplete. They’re built on averages — and averages don’t account for the Victorian terrace with zero side access, the drainage that needs rerouting, the steelwork hiding behind a wall no one knew about, or the conservation officer who has strong opinions about your roof pitch.
Two extensions with identical square footage can look nothing alike on a cost sheet. One is a straightforward rear extension with clean access and standard finishes. The other involves major structural alterations, bespoke detailing, and a logistics puzzle that takes weeks to plan properly. Same size on paper. Completely different projects in reality.
That gap between what the internet says and what a project actually costs is where a lot of London homeowners find themselves in difficulty.
The cheapest quote isn’t always a bargain.
It’s worth saying plainly, because we see it regularly.
Low quotations are often low for a reason – incomplete scopes, missing items, unrealistic provisional sums, or simply not enough management built in to keep a project moving properly. The price looks good until it doesn’t. Then come the variations, the delays, the conversations nobody wanted to have.
And while poor workmanship is ultimately the contractor’s responsibility, homeowners carry some responsibility too. Selecting a builder based purely on an unrealistic price – rather than experience, planning capability, and proper coordination – is a decision that tends to catch up with people.
In construction, unrealistic budgets rarely disappear. They reappear later as compromises, stress, delays, or additional costs.
A well-considered quotation reflects more than bricks and mortar. It reflects the planning, structural thinking, sequencing, coordination between trades, and project management required to actually deliver the work – correctly, first time.
That’s not a premium. That’s what a properly run project costs.
So what does realistic budgeting actually look like?
It starts well before anyone breaks ground.
At S&M Solutions, we put considerable emphasis on the pre-construction phase – layout coordination, structural review, buildability assessment, programme planning, specification development. Not because we enjoy paperwork, but because projects that are properly thought through at the outset go more smoothly, cost less in the long run, and cause significantly less stress along the way.
Careful preparation at the beginning almost always saves time and money later.
Not every project – or every client – is the right fit.
We work best with homeowners who value realistic budgeting, experienced coordination, transparent communication, and a properly planned Design & Build approach from concept through to completion.
That’s not for everyone, and we respect that. If the priority is finding the lowest possible upfront number, there are procurement routes better suited to that. We’d rather say so honestly at the start than waste anyone’s time.
What we offer is straightforward — experienced teams, honest advice, and a properly managed project from day one. For homeowners who value that, we’re a strong fit. For those still shopping purely on price, we’d gently suggest that approach carries more risk than it might appear.
Grand Designs makes it look seamless. It rarely is.
What you don’t see on television – or in any online guide – is the full weight of delivering a properly coordinated residential project in London. The compliance requirements. The specialist coordination. The site logistics in a dense urban area. The decisions that need to be made correctly and early, so they don’t become expensive problems later.
Broad online figures can occasionally provide a useful starting point. But they should be treated as exactly that – a starting point, not a budget.
Selecting the Right Procurement Approach
Let’s Discuss Your Project
Every project is different. Before relying on generic online figures or assumptions, speak with an experienced Design & Build team who can assess the scope, constraints, and likely budget requirements for your specific property.
If your project is based in London and you are looking for realistic advice, experienced coordination, and a properly planned approach from the outset, we would be pleased to hear from you.
If you’re planning a renovation, extension, or loft conversion in London and you want a realistic picture of what your project actually involves, we’re always happy to have that conversation before significant time or money is committed.No pressure. No obligation. Just an honest assessment of whether the scope, expectations, and budget appear commercially and technically viable.
Because the right conversation at the start of a project is worth considerably more than a number from the internet.
S&M Solutions Ltd works with London homeowners on residential extensions, loft conversions, and full renovation projects. We specialise in Design & Build delivery — from initial planning through to completion.
