The estimating glossary: NRM, BoQ, PC sums and friends

Estimating has a private language, half inherited from quantity surveying and half from site. If you have ever nodded along to "we'll carry that as a provisional sum against the prelims", this page is for you. Thirty terms, defined in plain English, grouped the way they actually get used.

The documents

• Bill of quantities (BoQ). The itemised list of everything a job needs: each task and material as its own measured line with a quantity, a rate and a total. The backbone of serious pricing, explained fully in what is a bill of quantities.
• Take-off. The act of measuring quantities from drawings: lengths of wall, areas of plaster, counts of sockets. The bill is the output, the take-off is the work.
• NRM (New Rules of Measurement). The RICS rulebook for how construction work should be measured and described, so that two estimators measuring the same drawing produce comparable bills. NRM2 is the part that covers detailed measurement for building works.
• Schedule of works. A descriptive list of jobs to be done, room by room or trade by trade, without full measured quantities. Lighter than a bill, common on refurbishments.
• Specification. The document describing quality and products: which block, which membrane, which finish. The drawings say where, the spec says what.
• Estimate vs quote. An estimate is an informed approximation that may move. A quote is an offer you intend to be held to. The difference matters legally and commercially, and we unpack it in estimate vs quote.
• Tender. A formal, competitive quote submitted against a defined set of documents, usually alongside other firms.

The sums

• Prime cost sum (PC sum). An allowance inside the quote for an item whose product is not yet chosen, typically the client's picks: sanitaryware, tiles, kitchen units. The labour to fit is priced; the item itself carries an allowance that gets trued up when the choice is made.
• Provisional sum. An allowance for work that cannot be fully defined yet, like "renew drainage if found defective". It signals honest uncertainty and gets replaced by real pricing once the facts exist.
• Lump sum. One fixed price for a defined scope. Clean when the scope is genuinely defined, dangerous when it is not.
• Contingency. Money held against the unknown, sized to the age and condition of the building. Whose money it is, and when it gets spent, should be written down.
• Dayworks. Work charged at agreed hourly or daily rates plus materials, used when pricing in advance is impossible. The agreed rates are the protection.

The money mechanics

• Preliminaries (prelims). The costs of running the site rather than building the thing: welfare, scaffold, skips, supervision, insurances, temporary services. Weekly by nature, and chronically under-priced, as we cover in preliminaries explained.
• Overheads. The cost of existing as a business: van, insurance, phone, software, yard, your unbillable hours. Every job must carry its share.
• Margin / profit. What is left after labour, materials, plant, prelims and overheads. Markup is added to cost; margin is the share of the price. Confusing the two flatters your numbers.
• Unit rate. The price per unit of a measured item: per square metre of plastering, per metre of footing. Rate times quantity gives the line total.
• Stage payments (interim payments). Money paid at agreed milestones through the job rather than one cheque at the end. Protects cash flow on both sides.
• Retention. A small percentage held back from payments until defects are put right, released after the defects period. Common in contract work; needs clear terms to be fair.
• Valuation. The periodic assessment of work done to date, used to calculate an interim payment.
• CIS (Construction Industry Scheme). The UK tax scheme under which contractors deduct money from subcontractor payments and pass it to HMRC.

The site vocabulary

• First fix. Everything before plastering: carcassing carpentry, cable runs, pipework in walls and floors.
• Second fix. Everything after plastering: sockets and switches, sanitaryware, doors, skirting, the visible finishing of services and joinery.
• Making good. Repairing surfaces disturbed by the works: patching plaster, redecorating around a new opening. Small words, real hours.
• Builder's work in connection (BWIC). The holes, chases, lintels and patching one trade needs so another can do its job. Classic forgotten money.
• Snagging. The list of small defects and unfinished details identified at the end of a job, to be corrected before final payment.
• Variation. A change to the agreed scope after the contract exists. Should always be priced and confirmed in writing before the work happens.
• Practical completion. The point at which the works are complete enough to be used as intended, triggering handover and usually the start of the defects period.
• Defects liability period. The agreed months after completion during which the builder returns to fix defects that emerge, often linked to the release of retention.

The contract corner

• JCT contracts. The most common family of standard building contracts in England and Wales, with versions scaled from small domestic jobs to major projects. Using a standard form beats improvising terms.
• Extension of time. A formal allowance of extra programme when delay arises from causes the contract says are not the builder's risk.
• Liquidated damages. A pre-agreed daily or weekly sum the client may deduct for late completion. Check it is realistic before signing, not after.
• Scope creep. The informal, unpriced growth of a job through small requests. Not a contract term, but the reason half the contract terms exist.

Putting the words to work

Knowing the terms is step one. Using them consistently in every quote is what changes outcomes, because each term is really a decision about who carries which risk. This is where tooling earns its keep: QS Quoter prices a full bill of quantities from a description or drawings at your own rates, and structures the result the way this glossary describes, with measured lines, sums where sums belong, and a private tradesman copy alongside the client copy. Every line stays editable, so the vocabulary stays under your control.