What Does a Quantity Surveyor Do in a London Renovation?

Cost overruns are the single most common complaint about London renovation projects. Clients commission work, receive quotes, approve budgets — and then watch the final number climb 20, 30, or 50 per cent beyond what was agreed. A quantity surveyor (QS) exists specifically to prevent this. This guide explains what a QS does, when you need one, and what to look for.

What is a quantity surveyor?

A quantity surveyor is a construction professional who specialises in the financial and contractual management of building projects. The core function is cost: measuring the scope of work, preparing cost plans, reviewing contractor quotes, managing valuations during the build, and assessing the validity of variations and claims.

The professional body in the UK is the Royal Institution of Chartered Surveyors (RICS). A chartered quantity surveyor holds the MRICS designation and is bound by the RICS Rules of Conduct. For significant residential renovation projects, instructing an MRICS-qualified QS provides professional accountability that a general contractor or project manager does not.

What does a QS do on a renovation project?

The QS role can be engaged at any stage of a project, but the value is greatest when engagement starts early.

Pre-contract: cost planning

Before a contractor is appointed, the QS:

• —Prepares a detailed cost plan based on the architect's drawings and specification. This is not a contractor's quote — it is an independent assessment of what the works should cost, built up from first principles using current London market rates.
• —Identifies cost risk — elements of the design or specification that carry significant cost uncertainty (structural works, specialist finishes, services upgrades) and where contingency should be held.
• —Reviews contractor quotes — when tenders come in, the QS compares them against the cost plan and identifies anomalies. A quote that is 20 per cent below the cost plan is not necessarily a bargain — it may reflect omissions that will reappear as variations.
• —Advises on contract form — whether a fixed-price contract, a cost-plus arrangement, or a schedule of rates is appropriate for the project.

During construction: cost control

Once work has started, the QS:

• —Certifies valuations — at agreed intervals (typically monthly), the QS assesses the value of work completed and certifies what payment is due to the contractor. This protects the client from overpaying for incomplete work.
• —Assesses variations — whenever the contractor claims additional cost for a change to the scope, the QS reviews the claim against the contract and current rates, and either agrees, negotiates, or disputes the amount. This is where QS value is most visible: contractor variation claims are routinely inflated, and a QS experienced in London residential work will know the going rates and where claims are padded.
• —Manages the contingency — a properly managed contingency is not a slush fund. The QS tracks actual cost against budget, forecasts the final account, and advises when contingency is being consumed faster than expected.
• —Maintains the cost report — a running document showing original budget, approved variations, forecast final cost, and contingency remaining. Updated monthly and shared with the client.

At completion: final account

At practical completion, the QS:

• —Agrees the final account with the contractor — the definitive statement of what is owed, taking into account all variations, provisional sums, and adjustments.
• —Reviews retention — retention is typically 3–5 per cent of the contract sum, held back until the defects liability period expires. The QS manages the release of retention at the appropriate time.
• —Advises on any claims — where the contractor submits a claim for loss and expense (delays, disruption), the QS assesses and responds.

When do you need a QS on a London renovation?

Not every renovation requires a dedicated QS. The threshold at which it makes economic sense is broadly:

QS fees typically run at 2–4 per cent of construction cost for full services. On a £500,000 renovation, a QS at 3 per cent costs £15,000. If the QS identifies and resolves £50,000 of inflated variation claims — which is not uncommon on London renovations of that scale — the return is clear.

The difference between a QS and a project manager

These roles are frequently confused. A project manager oversees the programme, the coordination of trades, and the delivery of the project on time. A quantity surveyor oversees the costs. On larger projects, both roles are present. On smaller projects, one person may carry both functions — but this is a compromise, and clients should be clear which function they are buying.

ASAAN provides project management on all our renovation commissions. For projects above £300,000, we recommend clients appoint an independent QS alongside our project management function — the separation of cost oversight from delivery management is a governance principle, not an inefficiency.

Choosing a QS in London

Key criteria:

• —MRICS qualification — verifiable on the RICS Find a Surveyor register
• —Residential experience in London prime — commercial QS practice and residential luxury renovation are different disciplines. Rates, contract norms, and the typical contractor behaviours they will encounter are specific to the London prime residential market.
• —Independence — the QS should be appointed directly by the client, not introduced or recommended by the contractor. A QS with a prior relationship with the contractor is not independent.
• —References — from clients of similar projects, not just from contractors

For ASAAN projects, we are happy to recommend independent QS practices we have worked alongside and whose work we have seen in practice. Get in touch to discuss. Related guides: our renovation contracts guide covers the contract structures a QS will be working within, and our budgeting guide covers cost planning from the client's perspective.