The truth is, most cost overruns on residential sites in Kenya start with a poorly prepared Bill of Quantities. A Bill of Quantities, or BOQ, is the document that breaks down every material, labour item, and cost element needed to construct a building, measured against a recognised standard method of measurement. If you are a quantity surveyor, contractor, or even a civil engineer handling small residential projects, this is a skill you need early in your career.
In this guide, you will learn what a BOQ is, how to prepare one step by step for a residential building, which measurement rules to apply, and the common mistakes that cause payment disputes on site.
Quick Answer: A Bill of Quantities for a residential building is prepared by taking off quantities from architectural and structural drawings, measuring each element using a recognised standard method of measurement, then billing the items with descriptions, units, and rates to produce a document contractors use for pricing, tendering, and valuation.
What Is a Bill of Quantities and Why Does It Matter
A BOQ is a priced or unpriced schedule of every item of work in a project, quantified from the drawings and described clearly enough that any contractor can price it the same way. It is the pricing backbone of a construction contract.
In simple terms, the BOQ answers one question for the contractor: exactly how much material and labour will this building consume, item by item. Without it, tendering becomes guesswork.
On residential sites, a poor BOQ shows up fast. A contractor either prices too high out of fear of the unknown, or too low and starts losing money by the time the roof goes up. Both outcomes lead to the same result: a stalled site and a frustrated client. This is why the BOQ is also the document quantity surveyors use later to value work done and process interim payments.
How to Take Off Quantities from Drawings, Step by Step
Preparing a BOQ starts long before you open a spreadsheet. It starts with the drawings.
- Study the architectural and structural drawings together. Cross-check dimensions between the two before you measure anything.
- Break the building into elements: substructure, superstructure, roofing, finishes, and external works.
- Take off quantities using dimension sheets, working systematically from substructure upward so nothing is measured twice or skipped.
- Apply a recognised standard method of measurement. Most Kenyan quantity surveyors work from principles in SMM7 and the RICS New Rules of Measurement (NRM2), adapted to local practice and NCA guidelines.
- Group the measured items into bill sections with clear descriptions, units, and quantities.
- Leave provisional sums for specialist work that cannot be fully measured at tender stage, such as some MEP installations.
Honestly, the take-off stage is where most errors happen. If you rush the drawing study, every quantity built on top of that mistake carries the error through the whole bill.
How to Structure the Bill Into Trades and Sections
Once quantities are taken off, they need to be organised into a structure a contractor can price section by section. A typical residential BOQ looks like this:
| Section | Example Items | Typical Unit |
|---|---|---|
| Preliminaries | Site mobilisation, insurance, water and power connection | Sum |
| Substructure | Excavation, hardcore filling, foundation concrete, DPC | m3, m2 |
| Superstructure | Columns, beams, slabs, blockwork | m3, m2, No. |
| Roofing | Trusses, purlins, roofing sheets, gutters | m2, m |
| Finishes | Plaster, paint, tiling, doors and windows | m2, No. |
| External works | Drainage, boundary wall, access drive | m, m2 |
This structure matters for two reasons. First, it lets the client compare bids from different contractors on a like-for-like basis. Second, it becomes the basis for valuing work done at each payment stage, so it needs to match how work will actually progress on site.
Common Measurement Rules Every Quantity Surveyor Must Apply
Standard methods of measurement exist so that two surveyors measuring the same building arrive at the same quantity. A few rules come up constantly on residential jobs.
Openings in walls above a set threshold, typically 0.5 square metres under SMM-based rules, are deducted from the wall area. Smaller openings are ignored because the labour saved in measuring them does not justify the time spent.
Unit rates are built up from four components: material cost, labour cost, plant cost, and a percentage for overheads and profit. Missing any one of these components under-prices the item and eats into the contractor’s margin later.
Provisional sums must be clearly flagged as estimates, not firm prices, so that when the actual scope is confirmed, the difference is treated as a variation rather than a dispute.
Common Mistakes That Cause Disputes on Site
A few recurring mistakes turn a BOQ from a pricing tool into a source of conflict.
- Vague item descriptions that leave room for different interpretations of scope.
- Failing to cross-check architectural and structural drawings before measuring, which creates quantity mismatches.
- Ignoring provisional sums or lump-summing items that should have been measured properly.
- Not updating the bill when drawings are revised, so the priced document no longer matches what gets built.
Each of these is avoidable with a disciplined take-off process and a habit of checking the bill against the latest drawing revision before it goes out to tender.
Frequently Asked Questions
Q: What is the difference between a BOQ and a BQ?
BOQ and BQ are the same document, Bill of Quantities, just written differently depending on the firm or country. Both refer to the priced or unpriced schedule of measured work items used for tendering and valuation.
Q: Who prepares the Bill of Quantities?
A quantity surveyor prepares the BOQ from architectural and structural drawings. On small residential projects without a dedicated QS, a civil engineer or experienced contractor sometimes prepares an approximate bill, though this raises the risk of measurement errors.
Q: What happens when actual site quantities differ from the BOQ?
The difference is treated as a variation. It is measured, valued at the contract rate where one exists, or a fair new rate is agreed, then documented and approved before it affects payment.
Conclusion
A Bill of Quantities is not paperwork. It is the financial map of a residential building, and getting it wrong costs real money on site. Master the take-off process, apply your standard method of measurement consistently, and keep every bill item traceable back to the drawings. That discipline is what separates a quantity surveyor clients trust with bigger contracts from one stuck on small jobs.
Want more practical construction knowledge delivered directly to you?
👉 Subscribe to our YouTube channel: https://www.youtube.com/@TheCivilEngineeringHub-001
PS: Join our engineering WhatsApp community for daily learning at +254731393520