The short answer
Not always. A quantity surveyor (QS) is a cost specialist who builds the budget, checks quotes and values the work as it is done. On a small, simple home project you can usually manage without one. On a large extension or new home, or when you tender to several builders, independent cost advice can pay for itself.
Most homeowners meet the term only when someone suggests one, usually halfway through a big project. This guide explains what a quantity surveyor does, when one earns their fee, and how choosing a design and build route changes the question.
Key takeaways
- A quantity surveyor specialises in construction costs: the cost plan, tender comparison, stage valuations and the final account.
- They are most useful early, when a cost plan can still change the design, and least useful once prices are already in.
- Large extensions, new homes and tendered projects benefit most, while small and simple jobs often do not justify a separate fee.
- On a design and build project the builder prices as the design develops, so the need for a separate quantity surveyor is usually smaller.
- Whoever you use, agree the scope and the fee in writing before they start.
What does a quantity surveyor do on a home project?
The Royal Institution of Chartered Surveyors (RICS) describes quantity surveyors as “the cost managers of construction”, and says they can be involved in the extension and refurbishment of a building as well as new construction. In practice, on a home project that means four jobs.
- The cost plan. An early estimate built from the first designs. Designing Buildings, the construction wiki, describes a cost plan as a “snapshot of the likely costs associated with construction works” that becomes more detailed as the design develops.
- The tender. Putting together the pack that builders price from, then comparing what comes back like for like.
- The valuations. Working out what has been properly completed at each stage, so each stage payment matches the work on site.
- The final account. Settling the finished cost, including any changes agreed along the way.
The tasks above are drawn from the Designing Buildings entry on the quantity surveyor, which also notes that chartered quantity surveyors pass the RICS Assessment of Professional Competence. What a QS does not do is design the building, produce structural calculations or run the site. That is the work of the architect, the structural engineer and the builder.
When is a quantity surveyor worth paying for?
Think of it as buying independent cost advice. It tends to earn its fee when one or more of these is true:
- The project is large or complex. A new home, a double storey extension or a whole house renovation has many more places for cost to drift than a single room.
- You are tendering to several builders. Someone has to make sure each builder priced the same scope, or the cheapest number may simply be the one that left things out.
- You want a budget check before you commit to a design. This is where a cost plan does the most good.
- You want independent valuations. Someone other than the builder checks each stage payment against the work done.
For a small, simple project with a clear design, a builder you trust and a written scope, a separate quantity surveyor is often more than the job needs. That is a judgement call rather than a rule, and a fair builder will talk it through with you.
| Route | Who prepares the cost advice | Where a QS may help |
|---|---|---|
| Architect, then tender to builders | The architect gives a rough guide, and each builder prices separately | Cost plan before tender, comparing tenders, checking valuations |
| Architect-led, with a QS appointed | The QS, alongside the design team | Throughout, from first drawings to final account |
| Design and build | The builder, as the design develops | Usually less needed, though some clients still want an independent check |
How does the order of the project affect when you need one?
The traditional route is a sequence: architect, planning, engineering, then tender. Craig Bellamy, founder of Madisons, explains it in his film on whether planning should be approved before you ask for prices: “So just keep it as a clean process: architect, planning submission, approval, engineer, take the whole pack, hand that out, tender to the builders, and then get yourself into a situation where you can start getting some tenders back.”
A quantity surveyor fits into that sequence at two points. The first is early, with the cost plan, while the design can still change. The second is at tender, when the finished pack goes out and the prices come back. The risk is the gap between them: a design agreed at planning can drift well beyond the original budget before anyone prices it properly. Our guide to planning an extension, step by step sets out where each stage falls.
Tip
Ask for a cost check when the first concept drawings exist, not after planning is approved. Changing a design on paper is cheap, and changing it after tender is not.
Do you need a quantity surveyor on a design and build project?
Usually less. In a design and build project, one company designs and builds under a single contract, so the cost is worked out as the design develops rather than after it is finished. That removes the stage where a separate cost consultant is most useful: the gap between a finished design and the first real prices.
Craig makes the same point in the same film: “Let’s start a design and build process where we can look after you from the start. We can look at budgets, where we are, build a project and planning award around what fits your budget, rather than the whole rollercoaster of emotions where you design something you just can’t afford.”
Some clients on a design and build route still want an independent cost check, and that is a reasonable choice. If you do, be clear about what the quantity surveyor will review: the specification, the allowances and the payment stages. For a view of what separates one quote from another, see why we are not the cheapest quote.
How do valuations and stage payments work with a QS?
On a project with a quantity surveyor, each stage payment is based on a valuation: a check of what has actually been built. Designing Buildings describes valuation statements for interim certificates as a core part of the role. It gives you something other than the builder’s word on how far the work has got.
Without a quantity surveyor, you and the builder agree the stages up front, and the payment schedule has to be clear enough to stand on its own. In his film on how builder payment stages work, Craig puts the principle simply: “for us as a contractor, we build your house with your money, because at the end of the day, it’s your house.” Whichever route you take, payments should follow work done, and the stages should be written down before you sign.
Watch out
A quantity surveyor controls cost, not scope. If the drawings and specification are vague, no one can price them reliably, and the saving you hoped for turns into arguments about what was included. It also pays to keep a contingency whichever route you choose.
How do you find and appoint a quantity surveyor?
- Decide what you want them to do. A one-off cost plan, tender support and valuations are different jobs with different fees.
- Look for a chartered firm. The RICS Find a Surveyor service lists regulated firms offering quantity surveying.
- Get two or three quotes. Compare what is included, not just the headline fee.
- Agree the fee basis in writing. Designing Buildings notes that fees are often a percentage of the contract cost, but can also be time-charged or fixed, and that RICS withdrew its last indicative fee scale in 2000. There is no standard rate to expect, so ask for a fixed fee where the scope allows.
- Brief them early. Give them the first drawings and your budget, and ask for a cost plan before you commit to the design.
The Designing Buildings guide to quantity surveyor fees sets out the usual bases. If you are weighing up an extension, our house extensions page shows how we run one from first sketch to handover.
Sources and further reading
- Quantity surveying, RICS Find a Surveyor
- Quantity surveyor, Designing Buildings
- Cost plan, Designing Buildings
- Quantity surveyor’s fees, Designing Buildings
Frequently asked questions
What does a quantity surveyor do on a house build?
A quantity surveyor manages the money side of a build. They prepare a cost plan from the early design, turn the drawings into measured quantities, help issue and assess tenders, value the work done for each stage payment and settle the final account. They do not design the building or run the site.
Is a quantity surveyor worth it for an extension?
It depends on the size and the unknowns. On a small, simple extension with a clear design and a builder you trust, a separate quantity surveyor is often more cost than the job needs. On a large extension, a new home or a project you are tendering to several builders, independent cost advice can be worth paying for.
Can a quantity surveyor check a builder’s quote?
Yes. Checking and comparing quotes is part of assessing tenders, and a quantity surveyor can show where two prices differ in scope, allowances or provisional sums. For the check to mean anything, every builder needs to have priced the same drawings and specification.
When should I appoint a quantity surveyor?
As early as the first design drawings, because that is when a cost plan does the most good. An early budget check can stop you paying for a design you cannot afford. Appointing one after the builders have already priced the job limits what they can usefully do.
How do I find a chartered quantity surveyor?
The Royal Institution of Chartered Surveyors runs a Find a Surveyor service that lists regulated firms offering quantity surveying. Approach two or three, ask what is included in the fee, and have the fee and scope agreed in writing before work starts.
