How Much Does a Home Extension Cost in Farnham in 2026? (And Why Most Quotes Are Wrong)
- mal909
- Apr 2
- 3 min read
If you’re planning a home extension, one of the first questions you’ll ask is:
“How much is this actually going to cost?”
In areas like Farnham, where property values are high and expectations are even higher, getting this wrong can be an expensive mistake.
At Forsyth Construction Surrey Ltd, we regularly speak to homeowners who have received multiple quotes from Builders in Farnham—but still don’t know which one is accurate.
Some look too high. Some look like a bargain.
👉 The reality is: they’re often not pricing the same job.
In this guide, we’ll break down:
What a home extension really costs in 2026
Why quotes vary so dramatically
And how to protect yourself from costly surprises
As a realistic guide for 2026:
Basic single-storey extension: £1,800 – £2,400 per m²
Mid-range extension: £2,400 – £3,000 per m²
High-spec / bespoke extension: £3,000+ per m²
So for a typical 25m² extension:
👉 £45,000 – £75,000+
However—and this is where most people go wrong—
These figures are only accurate if the quote is complete.
If key elements are missing or underestimated, the final cost can increase significantly during the build.
If you're currently researching builders in Farnham, start here:
⚠️ Why Some Quotes Look Cheap (But Aren’t)
It’s very common to receive two quotes for the same drawings that are £20k–£50k apart.
This doesn’t mean one builder is simply “more expensive”.
👉 It usually means they’re pricing different scopes of work.
Lower quotes often:
Omit structural elements
Underestimate labour requirements
Exclude finishes or key details
Include vague allowances (Provisional Sums)
On paper, it looks like a saving.
In reality, it often leads to:
👉 Unexpected costs, delays, and disputes mid-project
🔍 The Biggest Cost Mistakes Homeowners Make
1. Comparing totals instead of detail
A lower total price can be misleading.
👉 It often means less has been included—not that it’s better value.
2. Ignoring provisional sums
These are allowances—not fixed costs.
They frequently increase once work begins.
3. No contingency allowance
Every project carries unknowns.
Without a contingency:
👉 You’re financially exposed from day one.
4. Choosing based on price alone
This is the most expensive mistake.
The real risk isn’t overpaying—it’s committing to a quote that isn’t realistic.
🧠 How to Compare Builder Quotes Properly
Before choosing a builder, you should clearly understand:
What is fully included
What is estimated
What is excluded entirely
What assumptions have been made
If these aren’t clear:
👉 You are not comparing like-for-like quotes.
For a transparent approach to pricing and scope, contact us!
📍 Why Local Experience in Farnham Matters
Farnham projects come with specific challenges:
Planning sensitivities
Structural considerations
Access constraints
Material expectations in higher-value areas
A builder with local experience will:
Price more accurately
Identify risks earlier
Deliver a smoother, more predictable build
If your project involves structural work, this is especially important:👉 structural alterations in Farnham
📘 How to Avoid Costly Mistakes Before You Commit
Most issues don’t come from poor workmanship.
They come from:
Misinterpreted drawings
Incomplete quotes
Lack of clarity at the start
That’s exactly why I created a short guide:
It helps homeowners:
Identify missing elements in quotes
Understand realistic pricing
Avoid budget blowouts mid-build
Final Thoughts
A home extension is a major financial commitment.
Getting the right result isn’t about choosing the cheapest quote—
It’s about understanding the true cost of the project before you start.
If you’re planning an extension in Farnham, taking the time to get clarity now will save you stress, time, and money later.
📞
If you’d like a detailed, transparent quotation with no hidden surprises:
We specialise in:
Home extensions
Structural alterations
High-quality residential builds
Across Farnham, Guildford and Alton.
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