Most engineers can't articulate the difference between Bill of Quantities, Bill of Materials, and Technical Specification. Yet 80% of project value disputes happen because these three documents say different things. Here's how to align them.
Four ideas to carry into the next specification conversation you have.
Lists what gets paid for, in what units (no, m, m², lump sum). Prepared by QS. The basis for variations and progress invoicing.
Lists every nut, bolt, cable, fixture by manufacturer + model. Prepared by engineering. The basis for purchase orders and assembly.
Defines what 'compliance' means: standards, performance, warranty. Prepared by the consultant. The basis for inspection and rejection.
BOQ says 'LED downlight', generic. Spec says 'CRI > 90 + R9 > 50 + Tridonic driver + L70 50k h'. BOM says one specific model. Mismatch = arguments at commissioning.
Who owns it, who reads it, and what it actually controls.
| Document | Owner / audience | Controls |
|---|---|---|
| BOQ, Bill of Quantities | QS / Commercial / Client | Payment, variations, invoicing |
| BOM, Bill of Materials | Engineering / Procurement | Purchase orders, assembly, lot tracking |
| Specification (Spec) | Consultant / QC | Quality acceptance, rejection criteria |
| Drawings (incl. SLD) | Engineering / Site | Layout, routing, sizing |
| Datasheet | Manufacturer | Component-level performance |
| Method Statement | Contractor / HSE | How work is performed safely |
| ITP, Inspection & Test Plan | QC / Witness party | When and what to check during execution |
Five common gaps and how they cost projects money.
BOQ says '500 LED downlights, 12 W'. Spec says 'CRI > 80, R9 > 50, 3000 K, Tridonic driver, L70 > 50,000 h'. Contractor sources cheapest 12 W LED. At handover, consultant rejects. Now it's a variation order, and money fights.
BOQ is for 200 m of cable. BOM specifies 220 m (with wastage). Procurement buys 220 m. QS pays for 200 m. Contractor eats the difference. Multiply across all materials, that's why margins disappear.
Spec says 'minimum cable size 4 mm²'. SLD shows 2.5 mm² on a long run. Engineering missed the voltage drop. Site team installs 2.5 (cheaper, per drawing). Commissioning fails. Now everyone's pointing fingers.
Consultant's ITP says 'witness 100% of cable terminations'. Contractor's ITP says 'sample 10%'. When the gap is discovered, schedule slips because the consultant must witness everything from that point. Always reconcile ITPs at kick-off.
BOQ has 'cable, by metre' but the spec mandates a specific size only available in 305 m drums. The contractor buys whole drums; QS pays per metre laid. The waste is the contractor's loss, until they raise it as a claim. Match units.
Every NLC tender response includes a reconciled BOQ-BOM-Spec matrix showing line-by-line traceability. Zero ambiguity at handover.
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