What is the difference between a quantity surveyor and a building surveyor?

A quantity surveyor deals with the cost and commercial management of construction work. A building surveyor deals with the condition of existing buildings, diagnosing defects and specifying repairs. On a refurbishment project you may need both.

Is a quantity surveyor worth it on a domestic extension?

It depends on value and complexity. On smaller projects the benefit usually comes from a clear scope and comparable tenders. On larger or phased projects, monthly valuation and variation control are where the money is protected.

Why do contractors' quotations vary so much?

Usually because they have priced different things. Exclusions, allowances, preliminaries and assumed specification vary widely. Common tender documentation removes most of the difference.

Can you give me a cost per square metre?

Only as a very broad indication, with its base date and assumptions stated. Rates vary substantially with specification, access, location and market conditions, and a rate is never a quotation.

Quantity surveyor (construction cost consultant)

Quantity surveyors: keeping construction cost under control

What a quantity surveyor does: cost planning, tendering, valuing work in progress and administering the contract on building projects.

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Last reviewed 31 August 2026

What does a quantity surveyor do?

A quantity surveyor manages the money on a building project. That means estimating cost before design is fixed, measuring the work, running a competitive tender, valuing what has actually been built each month, pricing variations and agreeing the final account. A quantity surveyor is a cost consultant, distinct from a building surveyor, who deals with the condition of existing buildings.

At a glance

Appointed by: The client, so the cost advice is independent of the contractor's pricing.
Earliest value: Before design is fixed, when changing a decision still costs nothing.
Core outputs: Cost plan, tender documentation, interim valuations, variation pricing and final account.
Not the same as: A building surveyor, who diagnoses defects, or a valuer, who assesses property value.

Cost planning before commitment

The cheapest place to save money on a project is the drawing board. A cost plan attaches realistic figures to the design while options are still open, so the scheme can be shaped to the budget rather than cut back after tenders come in over.

A credible plan includes preliminaries, contingency and professional fees, states its base date and its assumptions, and is revisited as design develops. A single lump sum with no breakdown tells you nothing about where the risk sits.

Tendering on a like-for-like basis

Comparing three contractors' quotations only works if they priced the same scope. Tender documentation exists to force that comparison: defined scope, specification, and a pricing document each tenderer completes on identical terms.

Without it, the lowest number usually wins by excluding the most, and the difference reappears later as variations.

Payment, variations and the final account

During construction the quantity surveyor values the work properly executed each month, so payments track progress rather than optimism. Variations are priced as they arise, using the contract's mechanism, instead of being argued about at the end.

The final account then reconciles the contract sum with what was built, variation by variation. Projects that go badly wrong financially usually did so because nobody was doing this in real time.

Where this sits alongside surveying work

On refurbishment and repair projects the two disciplines overlap directly: a building surveyor establishes what is wrong and specifies the remedy, and cost consultancy turns that specification into a budget, a tender and a controlled payment process.

Who this is for

A good fit if

Homeowners running an extension, conversion or whole-house refurbishment
Landlords and owner-occupiers budgeting planned repair programmes
Buyers pricing the work a survey has identified before they exchange
Anyone holding widely varying contractor quotations and unsure why they differ

Not the right choice if

Diagnosing why a building is failing — that is defect investigation
Establishing a property's market value — that is a valuation
Structural design and calculations — that is a structural engineer

Cost and programme services

Instructions where cost, scope and evidence are the deliverable. Where a project needs a dedicated quantity surveyor, KJ will match you with one rather than stretch the wrong discipline over the work.

Planned maintenance programme

Prioritised, costed works over a defined term, with a stated base date.

Dilapidations survey

Quantifying and evidencing end-of-lease repair claims item by item.

Insurance reinstatement valuation

Rebuild cost including demolition, fees and current regulatory compliance.

Schedule of condition

The baseline record that keeps a later cost claim arguable on facts.

Measured building survey

Accurate drawings, without which quantities are guesswork.

Structural survey report

Detailed condition reporting where the extent of works is unclear.

Getting cost control right

Four moves that prevent most budget overruns.

1.Fix the scope before asking for prices
A written scope and drawings are what make quotations comparable.
Measured survey
2.Build in contingency openly
Refurbishment uncovers surprises. A stated contingency is honest budgeting, not padding.
3.Agree how variations will be priced
Before work starts, not when the first change arrives.
4.Value work monthly against progress
Paying ahead of progress is the single biggest risk on a domestic project.

When to bring in a specialist

Structural design, calculations and temporary works — structural engineer
Building regulations approval and inspection — local authority or approved building control
Contract drafting, disputes and adjudication — a construction solicitor
Defect diagnosis where the cause of failure is unclear — building surveyor

Common questions

Limitations and sources

Cost figures depend on scope, specification, location and market conditions. Any figure given carries an effective date and stated assumptions, and is not a quotation.
Cost advice is not a substitute for a contractor's priced tender for your specific project.
Contractual and legal consequences of a variation or a dispute are matters for your solicitor.

Source: RICS · checked August 2026

Source: UK Government · checked August 2026

Last reviewed 31 August 2026.

Where to go next

the lease and repair liability behind the spend — On let premises, who pays is a lease question before it is a cost question.
what actually needs doing — Cost advice is only as good as the diagnosis and specification behind it.
reinstatement cost for insurance — Rebuild cost is a cost exercise reported as a valuation figure.

Have a project to budget?

Tell KJ what you are building or repairing and where you are in the process, and you will get a straight answer on what cost support is worth having.

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KJ gives general guidance only and has not inspected your property. A professional opinion follows an inspection by a surveyor.