A bill of quantities is a structured, measured document listing all the work items, materials, and labour required to complete a construction project. In UK practice, the types of bills of quantities you select directly shape how risk is allocated, how tenders are compared, and how variations are valued throughout a contract. The five primary types recognised in UK construction are firm, approximate, elemental, trade-based, and provisional, each serving a distinct purpose depending on design completeness and procurement route. NRM2 compliance is the standard that underpins all of them, ensuring measurement consistency and fair tender comparison across the industry.
What are the main types of bills of quantities?
Five core BoQ types define current UK industry practice: firm, approximate, elemental, trade-based, and provisional. Each type reflects a different stage of design development and a different approach to managing cost and quantity risk.
Firm (lump-sum) BoQs
A firm BoQ contains fully measured, fixed quantities derived from completed design drawings. Contractors price against these quantities, and the total forms a lump-sum contract price. Because quantities are fixed before tender, the client carries minimal quantity risk. This format suits projects with complete design information and traditional procurement routes.
Approximate BoQs
An approximate BoQ uses estimated quantities based on incomplete or outline design information. The quantities are subject to remeasurement once construction is complete, meaning the final account reflects actual work done rather than the original estimate. This type suits projects where design is still evolving at tender stage, and it shifts more quantity risk to the client.
Elemental BoQs
An elemental BoQ organises work by building element: substructure, frame, roof, external walls, and so on. This structure mirrors how cost plans are built during early design stages, making elemental BoQs the preferred format for budget planning and client communication. They give a clear picture of where money is being spent across the building.
Trade-based BoQs
A trade-based BoQ organises work by contractor trade package: groundworks, concrete, brickwork, carpentry, mechanical, electrical, and so on. This format aligns directly with how subcontractors price and deliver work. It is the preferred format for detailed tender documentation and procurement, because each subcontractor receives a package relevant to their scope.
Provisional BoQs
A provisional BoQ includes placeholder items for work that cannot yet be fully defined. These placeholders, known as provisional sums, cover specialist or undefined elements such as artwork installations or complex ground investigation works. The sums are replaced with actual measured items as design develops. Provisional BoQs are common in complex or phased projects where some scope remains uncertain at tender.
Pro Tip: Never treat a provisional sum as a budget allowance you can ignore. Provisional sums are contractual placeholders, and their eventual replacement with measured items can significantly alter the final account.
How do BoQ types align with project stages and procurement?
Choosing the right BoQ type is a strategic procurement decision that fairly allocates quantity risks and prevents costly disputes. The wrong choice at the wrong stage creates administrative friction and, more seriously, contractual exposure.
The alignment between BoQ type and project stage works as follows:
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Early design stage. Use elemental BoQs for cost planning and client approval. They map directly onto RIBA Stage 2 and 3 cost plans, giving clients a clear breakdown by building element before design is fixed.
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Outline design with incomplete information. Use approximate BoQs when you need to go to tender before design is complete. Accept that remeasurement will be required and price the quantity risk accordingly.
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Completed design, traditional procurement. Use firm BoQs. The contractor prices fixed quantities, the client gets a lump-sum price, and variations are valued against original unit rates. This is the most common format for publicly procured projects.
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Design and build procurement. Trade-based BoQs work well here. Employers' Requirements often include a trade-based BoQ or schedule of works that subcontractors price directly, giving the main contractor clear package costs.
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Complex or phased projects. Incorporate provisional sums within a firm or approximate BoQ to handle undefined scope. The contractual role of provisional sums is to ring-fence uncertainty without leaving the contract open-ended.
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Subcontractor procurement. Trade-based BoQs are the standard. Subcontractors expect to receive a package organised by their trade, not a full elemental breakdown of the whole building.
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Remeasurement contracts. Approximate BoQs with clear remeasurement clauses protect both parties. The contractor knows quantities will be verified; the client knows the final account reflects actual work.
Pro Tip: If you are using a design and build route, consider preparing both an elemental BoQ for your own cost plan and a trade-based BoQ for subcontractor procurement. The two serve different audiences and should not be confused.
Understanding how cost plans evolve to BoQ is the practical skill that separates a competent quantity surveyor from an excellent one. The transition from elemental cost plan to trade-based tender document is where most cost slippage occurs.
Elemental versus trade-based BoQs: what is the real difference?
Elemental BoQs are excellent for early-stage budgeting but create friction during procurement, because subcontractors prefer trade-based formats for tender clarity. Understanding this distinction saves time and reduces repricing at tender stage.
| Feature | Elemental BoQ | Trade-based BoQ |
|---|---|---|
| Organised by | Building element (roof, frame, finishes) | Contractor trade (electrical, plumbing, brickwork) |
| Best used for | Early budgeting, client cost reporting | Subcontractor tendering, procurement packages |
| Client communication | High clarity | Lower clarity for non-specialists |
| Subcontractor usability | Poor. Subcontractors must extract their scope | High. Each trade receives a relevant package |
| Administrative complexity | Lower at cost plan stage | Higher to prepare, but cleaner at tender |
| NRM2 alignment | Strong for cost planning | Strong for measured works |
The practical implication for project managers is straightforward. An elemental BoQ produced at RIBA Stage 3 cannot simply be handed to a brickwork subcontractor and expected to generate a clean tender return. The subcontractor will either price conservatively to cover uncertainty or ask for clarification that delays the programme.
Trade-based BoQs facilitate subcontractor tendering and work delivery but may complicate early-stage budgeting compared to elemental layouts. The solution is to use each format for its intended purpose rather than trying to make one document serve both functions.
Pro Tip: When converting an elemental cost plan into trade packages for tender, use a cross-referencing matrix to map elemental budget lines to trade packages. This prevents scope gaps and double-counting, which are the two most common sources of tender error.
Common misconceptions about bills of quantities
Several persistent misunderstandings cause real problems in practice. Knowing them protects you from tendering errors and contractual disputes.
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BoQ versus Schedule of Rates. A priced BoQ includes quantities and rates, whereas a Schedule of Rates lists rates only, without fixed quantities. Confusion between the two leads to tendering errors, because a Schedule of Rates cannot produce a fixed contract sum without measured quantities.
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BoQs as estimates. A BoQ is not an estimate. Once priced and incorporated into a contract, it becomes an enforceable document. Treating it as a rough guide exposes you to disputes over variations and final accounts.
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NRM2 as optional. NRM2 compliance is critical to ensure variations can be priced fairly against original unit rates, avoiding contractual disputes. Non-compliant BoQs create ambiguity that contractors will exploit at variation stage.
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Small projects do not need BoQs. Many builders use internal simplified BoQs to standardise cost control and avoid margin erosion, even when formal BoQs are not provided by clients. A simplified internal BoQ on a £50,000 extension protects your margin just as effectively as a full NRM2 document on a £5m scheme.
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BoQs are static documents. A BoQ is a living document. Variations, remeasurement, and provisional sum instructions all change it during the contract. Managing it as a static snapshot is a common cause of final account disputes.
"The BoQ is the enforceable language between client and contractor. Its primary purpose extends beyond merely listing items. It is the benchmark for contract and variation management throughout the life of the project."
BoQs serve as enforceable contract benchmarks, and their accuracy underpins every variation instruction, interim valuation, and final account negotiation. Getting the type right from the start is not an administrative detail. It is a commercial decision.
Key takeaways
Selecting the correct BoQ type from the outset is the single most effective way to control cost risk and prevent disputes on a UK construction project.
| Point | Details |
|---|---|
| Five recognised BoQ types | Firm, approximate, elemental, trade-based, and provisional each serve a distinct project stage. |
| NRM2 compliance is non-negotiable | Non-compliant BoQs create variation disputes and undermine the contract's enforceability. |
| Elemental BoQs suit budgeting | Use elemental formats for cost planning; switch to trade-based formats for subcontractor procurement. |
| BoQs are contractual documents | A priced BoQ is not an estimate. It is an enforceable benchmark for variations and final accounts. |
| Internal BoQs protect small builders | Simplified internal BoQs prevent margin erosion even on projects without client-prepared documents. |
Why BoQ selection is more consequential than most professionals realise
I have reviewed final accounts on projects where the wrong BoQ type was selected at tender, and the pattern is always the same. The quantity surveyor produced an elemental BoQ because that is what the cost plan looked like, handed it to subcontractors, and then spent six months untangling scope gaps during construction. The problem was not the measurement. The problem was the format.
The BoQ is the commercial spine of a project. Every variation instruction, every interim valuation, and every final account negotiation traces back to it. When the format does not match the procurement route, you create administrative friction that costs time and money at every stage.
My strongest recommendation is to engage a quantity surveyor familiar with NRM2 standards before design is complete, not after. The BoQ type should be decided at the same time as the procurement strategy, not as an afterthought once drawings are issued. Treating the BoQ as a living document, updating it as provisional sums are instructed and variations are agreed, is what separates projects that close cleanly from those that end in dispute.
Accuracy in the BoQ is not just good practice. It is the foundation of contractor trust, and contractor trust is what keeps a project on programme.
— Michael
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FAQ
What is a bill of quantities?
A bill of quantities is a structured document listing all measured work items, materials, and labour required for a construction project. In UK practice, it is prepared in accordance with NRM2 and used for tendering, cost control, and variation management.
What are the five types of bills of quantities?
The five primary types are firm, approximate, elemental, trade-based, and provisional. Each type suits a different project stage and procurement method, from early budget planning through to subcontractor tendering.
What is the difference between a BoQ and a Schedule of Rates?
A BoQ includes both quantities and rates, producing a fixed contract sum. A Schedule of Rates lists rates only, without fixed quantities, and cannot produce a lump-sum price without separate measurement.
Do small builders need a bill of quantities?
Simplified internal BoQs help builders maintain cost control and protect margins even on projects where clients do not provide formal documentation. The discipline of measuring work before pricing it applies regardless of project size.
What does NRM2 compliance mean for a BoQ?
NRM2 is the RICS New Rules of Measurement that governs how construction works are measured in the UK. An NRM2-compliant BoQ ensures that variations are priced consistently against original unit rates, reducing the risk of contractual disputes at final account stage.