Preparation of Specifications is a critical step in producing accurate and comprehensive bills of quantities (BoQ) in civil engineering projects in Kenya. It involves detailing the quality, workmanship, and materials to be used, ensuring all project requirements are clearly communicated to contractors and stakeholders. This process is guided by standardized methods such as the Standard Method of Measurement (SMM) and the Civil Engineering Standard Method of Measurement (CESMM), which promote consistency and transparency. Cross-referencing specifications with drawings and designs ensures alignment between the documented requirements and the physical project scope.

3.1 Preparation of Specifications

3.1.1 Specifications preparations

Specification preparation in civil engineering is the detailed documentation of requirements for materials, workmanship, and quality standards to be used in a construction project. This ensures all parties have a clear understanding of expectations, reducing ambiguity and potential disputes during execution. The preparation process involves several key steps to develop clear, measurable, and enforceable specifications that align with project objectives.

Specification = Material Requirements + Workmanship Standards + Quality Criteria

3.1.1.1 Material

A material specification is the part of the specification that states exactly what materials and products must be used in the works, including their type, quality, grade, size, standard, source, testing, delivery and storage. It allows the quantity surveyor to price the bill of quantities correctly, the contractor to buy the right materials, and the engineer or clerk of works to accept or reject materials delivered to site. Material clauses usually refer to recognised standards, such as Kenya Standards (KS) issued by KEBS or British and European standards, and they state that materials must be new, of the best quality of their kind and approved before use. Example: the specification for a maternity wing at a mission hospital in Kapsabet required cement complying with the relevant Kenya Standard, clean washed river sand and 20 mm crushed ballast from an approved quarry, so that every contractor priced the same materials.

Information Included in a Material Specification

• Type and description: The exact material, such as ordinary Portland cement, high-yield deformed bars or machine-cut stone.
• Grade, class or strength: The required performance level, such as class 25 concrete or grade 500 reinforcement.
• Size and dimensions: Sizes, thicknesses, gauges or grading, such as 200 mm walling stone or 28-gauge roofing sheets.
• Standard to be complied with: The KS, BS or EN standard that the material must meet.
• Source and approval: Approved sources, suppliers or quarries, and whether samples must be approved before ordering.
• Testing and certification: Tests required and test certificates or KEBS marks to be provided.
• Delivery, handling and storage: How materials are to be delivered, protected and stored on site.
• Alternatives: Whether alternatives "or equal approved" are allowed and how they are approved.

Steps for Writing a Material Specification

1. List all materials: Identify every material shown on the drawings and in the bill of quantities.
2. Determine performance needs: Decide the strength, durability and appearance each material must achieve.
3. Select applicable standards: Identify the KS, BS or EN standards that each material must comply with.
4. State grades and sizes: Write the exact grade, class, size and dimensions required.
5. Specify sampling and testing: State the samples, tests and certificates required before and during use.
6. Specify delivery and storage: State how materials must be delivered, handled and stored to prevent damage.
7. State approval procedures: Describe how samples and alternatives will be approved.
8. Check against drawings and BoQ: Ensure the material descriptions agree with the drawings and bill items.

Worked Examples

Example 1: Prepare a specification for concrete mix to be used in the foundation of a hospital building with a compressive strength of 25 MPa.

Given: Required compressive strength = 25 MPa

Specification requirement = Concrete mix design with f_c = 25 MPa

Answer: Specify concrete mix with minimum compressive strength of 25 MPa at 28 days curing.

Example 2: Specify the type of reinforcement steel for beams in a retail complex requiring yield strength of 500 MPa.

Given: Yield strength = 500 MPa

Specification = Use of high yield deformed bars with f_y = 500 MPa

Answer: Reinforcement steel specified as high yield deformed bars with yield strength of 500 MPa.

Example 3: Prepare a specification for waterproofing treatment on a hotel basement wall.

Given: Waterproofing membrane with minimum thickness 1.5 mm

Specification = Application of waterproofing membrane with t = 1.5 mm

Answer: Basement walls to receive waterproofing membrane of minimum 1.5 mm thickness.

3.1.1.2 Workmanship

A workmanship specification is the part of the specification that describes how the work must be carried out, including the methods, sequence, skill, accuracy, tolerances, curing, protection and finishing required for each trade. While the material specification ensures the right materials are bought, the workmanship specification ensures that they are put together correctly, because even the best materials fail if they are poorly mixed, placed, fixed or protected. Workmanship clauses also state how completed work will be inspected and tested, and what happens if it does not comply. Example: the specification for a dormitory block at a girls' secondary school in Kakamega required blockwork to be laid in stretcher bond with 10 mm joints, hoop iron every third course and curing for seven days, which the clerk of works used to inspect every wall.

Information Included in a Workmanship Specification

• Methods of construction: How each operation is to be done, such as mixing, placing and compacting concrete.
• Sequence of work: The order in which operations must be carried out, such as damp-proof course before walling above.
• Accuracy and tolerances: Allowable deviations in level, line, plumb and dimensions.
• Curing and protection: How fresh work must be cured and protected from weather and damage.
• Skill and supervision: Requirements for skilled tradespeople and competent supervision.
• Inspection and testing: Stages at which work must be inspected and tests carried out.
• Making good and cleaning: Requirements for repairing defects and leaving work clean.
• Removal of defective work: The contractor's obligation to remove and replace work that does not comply.

Steps for Writing a Workmanship Specification

1. Identify the work sections: List the trades involved, such as excavation, concrete, masonry, roofing and finishes.
2. Describe each operation: Write clear instructions for how each operation must be carried out.
3. State the sequence: Specify the order of operations and any hold points before the next stage.
4. Set tolerances: State the allowable deviations in line, level, plumb and dimensions.
5. Specify curing and protection: State how and for how long work must be cured and protected.
6. Specify inspection and testing: State inspection stages, tests and acceptance criteria.
7. State remedies for defects: Explain how defective work will be dealt with.
8. Review with the design team: Confirm the clauses agree with the drawings, design assumptions and contract conditions.

Worked Examples

Example 1: Prepare a workmanship specification for block laying in a county government office construction to ensure alignment and bonding.

Given: Workmanship criteria includes verticality tolerance ±3 mm per meter.

Specification = Block laying with verticality tolerance ±3 mm/m

Answer: Blocks to be laid with verticality tolerance not exceeding ±3 mm per meter length.

Example 2: Specify the curing period for concrete slabs in a school construction project.

Given: Minimum curing period = 7 days

Specification = Curing of concrete slabs for a minimum of 7 days

Answer: Concrete slabs to be cured for at least 7 days to achieve required strength.

3.1.2 Following SMM/CESMM standards

The Standard Method of Measurement (SMM) and Civil Engineering Standard Method of Measurement (CESMM) are essential frameworks that standardize how quantities and specifications are prepared in civil engineering projects. SMM is primarily used for building works, while CESMM applies to civil engineering works such as roads, drainage, and earthworks. Adhering to these standards ensures uniformity, reduces errors, and facilitates fair tendering and contract administration.

Quantity Measurement → (SMM or CESMM) → Standardized Bill of Quantities

Worked Examples

Example 1: Using SMM, measure the quantity of 200 mm thick concrete wall with dimensions 5 m length and 3 m height.

Given: Thickness = 0.2 m, Length = 5 m, Height = 3 m

Volume = Length × Height × Thickness

Volume = 5 × 3 × 0.2

Volume = 3 m³

Answer: Concrete wall volume = 3 m³ according to SMM.

Example 2: Apply CESMM to measure earthworks excavation for a trench 10 m long, 1.5 m wide, and 2 m deep.

Given: Length = 10 m, Width = 1.5 m, Depth = 2 m

Volume = Length × Width × Depth

Volume = 10 × 1.5 × 2

Volume = 30 m³

Answer: Earthworks excavation volume = 30 m³ per CESMM.

Example 3: Calculate the quantity of reinforcement steel bars measured in kilograms for a beam requiring 100 meters of 16 mm diameter bars.

Given: Length = 100 m, Diameter = 16 mm

Density of steel = 7850 kg/m³

Cross-sectional area A = π × d² ÷ 4

A = 3.1416 × (0.016)² ÷ 4

A = 0.000201 m²

Weight per meter = A × density

Weight per meter = 0.000201 × 7850

Weight per meter = 1.577 kg/m

Total weight = Weight per meter × Length

Total weight = 1.577 × 100

Total weight = 157.7 kg

Answer: Reinforcement steel weight = 157.7 kg.

Example 4: Using SMM, measure external wall plastering area for a wall 6 m long and 3 m high.

Given: Length = 6 m, Height = 3 m

Area = Length × Height

Area = 6 × 3

Area = 18 m²

Answer: Plastering area = 18 m².

Example 5: Measure the volume of concrete for a column 0.4 m by 0.4 m cross-section and 3 m height using CESMM.

Given: Width = 0.4 m, Depth = 0.4 m, Height = 3 m

Volume = Width × Depth × Height

Volume = 0.4 × 0.4 × 3

Volume = 0.48 m³

Answer: Column concrete volume = 0.48 m³.

3.1.3 Cross-referencing with drawings and designs

Cross-referencing specifications with drawings and designs is essential to verify consistency and completeness in civil engineering projects. This process ensures that the quantities and descriptions in the bill of quantities accurately reflect the project scope as depicted in the technical drawings. It involves systematic comparison and validation between the specification document and the design documents.

Accurate documents: specifications, drawings and designs must agree on every item

Worked Examples

Example 1: Verify wall length specified in the BoQ matches the drawing dimension of 8 m.

Given: Drawing length = 8 m, BoQ length = 7.5 m

Check: does 8 m equal 7.5 m?

Difference = 8 − 7.5 = 0.5 m

Answer: Discrepancy of 0.5 m, update BoQ to match drawing length of 8 m.

Example 2: Confirm concrete slab thickness in specification is consistent with design drawing of 150 mm.

Given: Drawing thickness = 150 mm, Specification thickness = 140 mm

Difference = 150 − 140 = 10 mm

Answer: Specification thickness is 10 mm less than design; revise to 150 mm.

Example 3: Cross-check reinforcement spacing specified in BoQ with design drawing showing 200 mm centre-to-centre spacing.

Given: BoQ spacing = 250 mm, Drawing spacing = 200 mm

Difference = 250 − 200 = 50 mm

Answer: BoQ spacing does not conform; adjust to 200 mm as per design.

Example 4: Validate the window opening dimensions in specifications against architectural drawings: 1200 mm width and 1500 mm height.

Given: Drawing width = 1200 mm, height = 1500 mm; Specification width = 1200 mm, height = 1500 mm

Check: Dimensions match.

Answer: Specification dimensions match drawings; no change required.

Example 5: Check the quantity of bricks specified for a wall of 10 m length, 3 m height, and 230 mm thickness against drawing dimensions.

Given: Wall dimensions same as above; Brick size 230 mm × 110 mm × 75 mm, laid with 10 mm mortar joints

Wall volume = Length × Height × Thickness

Wall volume = 10 × 3 × 0.23

Wall volume = 6.9 m³

Each brick occupies its own volume plus a 10 mm joint on each face, so the nominal size is 240 mm × 120 mm × 85 mm.

Volume per brick with mortar = 0.24 × 0.12 × 0.085

Volume per brick with mortar = 0.002448 m³

Number of bricks = Wall volume ÷ Volume per brick with mortar

Number of bricks = 6.9 ÷ 0.002448

Number of bricks = 2,819 bricks

Number of bricks with 5% wastage = 2,819 × 1.05 = 2,960 bricks

Answer: About 2,819 bricks are needed (about 2,960 including 5% wastage); ensure the BoQ matches this. Dividing by the brick volume alone, without allowing for mortar joints, would overestimate the number of bricks.

Chapter Summary

This chapter covers the essential steps in preparing a bill of quantities, beginning with the development of clear and detailed specifications. It emphasizes the importance of defining material requirements and workmanship standards while adhering to SMM and CESMM guidelines. The preparation process includes thorough cross-referencing with drawings and designs to ensure accuracy. Next, the chapter addresses the calculation of schedule of rates by abstracting quantities, applying standard costing methods, and adjusting rates to reflect specific project conditions. Accuracy and adherence to costing guidelines are highlighted as critical for reliable estimates. Finally, the compilation of the bill of quantities is discussed, focusing on using working drawings, maintaining comprehensiveness, following standard formats, and reviewing the document to ensure consistency with the prepared specifications. This systematic approach ensures that the bill of quantities is a precise and dependable document for project costing and management.