Costs

Extension or Move? How to Decide | Homeowner Guide

By John · 5 March 2026

The Big Decision

Extension or Move? How to Decide | Homeowner Guide matters most when a homeowner is close to making a decision and does not want a vague quote, soft assumption, or missing line item to become an expensive problem later.

Cost of Moving

On a £400k house:

Estate agent (1.5%): £6,000.
Conveyancing: £2,000.
Stamp duty (on new property): £10,000+.
Removal costs: £1,500.
Surveys/searches: £1,000.
Misc (address changes, etc.): £500.

Total: £21,000+ just to move

Plus:

Stress of selling/buying.
Chain risks.
Disruption to schools.
New area adjustment.

Cost of Extending

Typical 25 sqm extension:

Build cost: £60,000-80,000.
Architect: £3,000-5,000.
Fees/surveys: £2,000.
Temporary accommodation: £0-5,000.

Total: £65,000-90,000

But:

No stamp duty.
No chain.
Stay in your area.
Design exactly what you want.

Value Added

Extensions typically add:

50-70% of cost to property value.
So £70k extension might add £35-50k value.

But you also get:

The space you need NOW.
No moving stress.
Known neighbourhood.

When to Move Instead

Need more bedrooms than extension allows.
Garden too small and can't change.
Want different area/schools.
Property has fundamental issues.
Extension would cost more than value gap.

The Calculation

Cost to move to suitable house: A Stamp duty + fees: B Total move cost: A + B

Current house value: C Extension cost: D New value after extension: E

If (A + B) > (D - (E - C)), extend.

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Need help with the numbers? [Get an independent review](/#get-started) from The Building Guys.

Next Step

If you want help applying this to your own project, use the right route below.

Start with [Quick Review](/quick-review) if you want a fast first check.
Use [Builder Quote Review](/builder-quote-review) if you already have a quote in hand.
See the [Sample Report](/sample-report) if you want proof before you buy.

Frequently Asked Questions

Why does extension or move house matter so much?

Because extension or move house often sits right at the point where money, scope, and risk meet. If the paperwork is vague here, homeowners usually discover the problem after they have already committed.

Should I ask the builder more questions before I agree?

Yes. Clear builders should be able to explain what is included, what is excluded, and what assumptions sit behind the price.

Is a quick review enough?

Sometimes, yes. If you only need a first sense-check, start with [Quick Review](/quick-review). If you already have a proper quote or more serious concern, use [Builder Quote Review](/builder-quote-review).

What if I want proof before I buy?

Look at the [Sample Report](/sample-report). It shows the kind of clear, practical output we are aiming to give homeowners before they sign anything.

Practical Questions to Ask Before You Commit

When homeowners are dealing with extension or move house, the safest move is usually to slow the decision down and ask a few direct questions in writing.

What exactly is included in the current price?
What assumptions are being made that could change later?
Which items are still provisional, estimated, or allowance-based?
What would trigger a variation or extra cost?
What needs clarifying before any deposit or approval is given?

Short questions like these often reveal whether the paperwork is genuinely solid or simply looks tidy at first glance.

The Safer Way to Use This Advice

Use this article as a filter, not as a substitute for proper review. If the issue still feels unclear after reading, that is usually the sign that a real second opinion is worth getting.

A Final Word on Extension Or Move House

Extension Or Move House is worth checking before you commit.
A weak decision around extension or move house usually gets more expensive later.
Clear paperwork around extension or move house protects the homeowner, not just the builder.
If extension or move house still feels vague, get a second opinion before money moves.