If you have ever looked at a thick document full of item descriptions, units, and rates attached to a construction tender, you were looking at a Bill of Quantities. For quantity surveyors, contractors, and even civil engineers who work closely with cost teams, this document is the backbone of every serious construction project.
The truth is, a badly prepared BOQ causes more site disputes than almost anything else. Wrong quantities lead to wrong tender sums, and wrong tender sums lead to variations, claims, and strained client relationships. So getting this process right matters, whether you are a QS student, a young engineer, or a site professional who needs to understand where the numbers in a contract come from.
Quick Answer: A bill of quantities for a residential building in Kenya is prepared by taking off measurements from approved architectural and structural drawings, converting them into standard units using the Standard Method of Measurement, then billing and pricing each item to produce a document contractors use to tender.
What Is a Bill of Quantities and Why Does It Matter
A Bill of Quantities, commonly called a BOQ, is a document that lists every item of work needed to complete a building, with its unit of measurement and quantity. Contractors use it to price a project during tendering, and once a contract is signed, it becomes the basis for valuations, variations, and final accounts.
In simple terms, the BOQ turns a set of drawings into a priceable list. Without it, contractors would each measure differently, and the client would receive tenders that are impossible to compare fairly. That is the entire point of the document: it puts every bidder on the same measurement basis.
For a residential building in Kenya, the BOQ typically follows trade sections such as preliminaries, excavation and earthworks, concrete work, masonry, roofing, doors and windows, finishes, and external works.
Step 1: Gather Complete and Approved Drawings
You cannot measure what has not been designed. Before taking off a single quantity, confirm you have the full set: architectural drawings, structural drawings, and where available, the specifications document.
Incomplete drawings are the single biggest cause of BOQ errors on site. If the structural engineer has not finalized beam and column sizes, or the architect has not confirmed door and window schedules, any quantities taken at that stage will need revision later. Honestly, most rework on a BOQ traces back to someone measuring from an unapproved drawing.
Before starting, check that:
- Drawings are the latest revision, not a superseded version.
- Structural and architectural drawings match each other on dimensions.
- Specifications for materials (e.g. concrete grade, block type) are attached or confirmed.
Step 2: Take Off Quantities Using a Standard Method
Taking off is the process of measuring quantities of work directly from the drawings. In Kenya, most private and public projects reference the Standard Method of Measurement (SMM), often aligned with the RICS-based SMM7 or the newer NRM (New Rules of Measurement), with adjustments for local practice.
Each trade has its own measurement rules. For example:
| Trade | Typical Unit | Example Item |
|---|---|---|
| Excavation | Cubic metres (m³) | Excavate foundation trench, average depth 1.2m |
| Concrete | Cubic metres (m³) | 1:2:4 concrete in strip foundation |
| Blockwork | Square metres (m²) | 200mm blockwork in cement mortar 1:4 |
| Reinforcement | Kilograms (kg) or Tonnes | High yield steel bars to BS 4449 |
| Roofing | Square metres (m²) | 28 gauge iron sheets on timber trusses |
| Doors/Windows | Number (No.) | Panel door complete with ironmongery |
Quantities are worked out using dimension sheets, where length, width, and height (or depth) are recorded, then squared into totals. Any competent QS keeps these working sheets as backup, because a client or auditor can ask for them during a valuation dispute.
Step 3: Prepare Abstract and Bill the Items
Once all trades are measured, quantities are collected into an abstract, which groups similar items together and removes duplication. From the abstract, the actual bill is drawn up in the standard trade order, with each item given a clear description, unit, and quantity, followed by columns for rate and total amount that the contractor fills in during tendering.
A well-written item description leaves no room for a contractor to price ambiguously. For example, “supply and lay hardcore, well compacted, 150mm thick” is measurable and enforceable. A vague description like “hardcore filling” invites disputes later when the contractor claims a different thickness was priced.
Step 4: Add Preliminaries and Provisional Sums
Preliminaries cover site establishment costs: site office, security, insurance, water and electricity connections during construction, and general site supervision. These are billed separately, usually as a lump sum or percentage, and they matter because contractors sometimes under-price preliminaries to appear cheaper on the main bill.
Provisional sums are included for items that cannot be fully defined at tender stage, such as external services connections whose exact scope depends on utility company requirements. The Kenya Building Code and the current Public Procurement and Asset Disposal Act provisions both expect provisional sums to be clearly flagged, not hidden inside other trades.
Frequently Asked Questions
Q: What software is commonly used to prepare a BOQ in Kenya?
Most QS professionals use Excel for smaller residential projects, since it gives full control over formulas and formatting. Larger firms use dedicated software like CostX, Buildsoft, or WinQS for bigger commercial and infrastructure projects.
Q: Who is responsible for preparing the BOQ, the QS or the contractor?
On a standard contract, the client’s quantity surveyor prepares the BOQ during design and tendering. The contractor only fills in rates and totals. On design-and-build contracts, the contractor’s own QS may prepare it instead.
Q: How accurate should a BOQ be before tendering?
It should be accurate enough that contractors can price with confidence and the client can compare tenders fairly. Minor adjustments during construction are normal, but major quantity errors at tender stage signal poor drawing coordination or rushed take-off.
Conclusion
A bill of quantities is only as good as the drawings and discipline behind it. Get the drawings right, measure to a recognised standard, describe items clearly, and separate preliminaries from provisional sums, and you have a BOQ that protects both the client and the contractor from disputes down the line. This is a skill worth mastering early, whether you are heading into quantity surveying, site management, or structural engineering.
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