The preparation of tender documents is a critical phase in the quantity surveying process, as it sets the foundation for fair competition and accurate pricing. In Kenya, quantity surveyors must ensure that the tender documents are comprehensive, clear, and compliant with local construction standards and procurement regulations. Among the key components of tender documents are the working drawings, which provide the detailed visual instructions required for construction. This section focuses on the preparation of working drawings, essential for accurate estimation and successful project execution.

2.1 Preparation of working drawings

2.1.1 Purpose and importance of working drawings

Working drawings serve multiple purposes in construction projects and are crucial for quantity surveyors when preparing tender documents.

• Detailed project visualization: They translate design concepts into detailed representations, showing dimensions, materials, and construction methods, which help contractors understand the project fully.
• Basis for quantity takeoff: Quantity surveyors use these drawings to measure quantities accurately, ensuring precise cost estimation and budgeting.
• Communication tool: They facilitate clear communication among clients, contractors, engineers, and other stakeholders, reducing misunderstandings.
• Compliance and approvals: Working drawings demonstrate adherence to local building codes and standards, necessary for obtaining construction permits.
• Contractual reference: Once the contract is awarded, these drawings form part of the contract documents and are used to verify progress and quality.

2.1.2 Types of working drawings relevant to quantity surveyors

Quantity surveyors must be familiar with various types of working drawings, each serving distinct roles in the tendering process.

• Architectural drawings: Show building layouts, elevations, sections, and details, providing the overall design framework.
• Structural drawings: Detail the framework supporting the building, including foundations, beams, columns, and slabs.
• Mechanical and electrical drawings: Illustrate installations such as plumbing, HVAC, wiring, and lighting, essential for specialized works.
• Civil engineering drawings: Include site plans, drainage, roads, and earthworks, relevant for infrastructure projects.
• Finishing and landscaping drawings: Depict surface finishes, external works, and landscaping elements that affect final costs.

2.1.3 Steps in preparing working drawings for tender documents

The preparation of working drawings involves a systematic process to ensure accuracy and completeness.

1. Review design briefs and specifications: Understand client requirements, design intent, and applicable standards.
2. Coordinate with design professionals: Collaborate with architects, structural and services engineers to integrate all design aspects.
3. Draft preliminary drawings: Prepare initial sketches showing general layout and key structural elements.
4. Incorporate detailed information: Add dimensions, materials, construction methods, and technical notes.
5. Verify compliance: Ensure drawings conform to Kenyan building codes and regulations.
6. Finalize and approve drawings: Obtain necessary approvals from clients and regulatory authorities before inclusion in tender documents.

2.1.4 Common challenges in preparing working drawings and how to address them

Working drawings preparation can encounter challenges that affect tender accuracy and project execution.

Challenges

• Incomplete design information: Missing details can lead to inaccurate quantity takeoffs and cost overruns.
• Coordination issues: Lack of communication between design teams results in conflicting drawings.
• Non-compliance with standards: Drawings not adhering to local codes cause delays in approvals.
• Frequent design changes: Late modifications increase rework and confusion.
• Technical complexity: Highly technical systems require specialized knowledge to represent correctly.

How to address challenges

• Early collaboration: Engage all design disciplines from the start to ensure integration.
• Regular reviews: Conduct drawing audits to detect and correct inconsistencies promptly.
• Training and capacity building: Equip quantity surveyors with knowledge of local codes and technical aspects.
• Change management: Implement a formal process to handle design revisions and communicate updates.
• Use of technology: Employ CAD and BIM tools to improve accuracy and coordination.

Worked Solutions for Practice Questions

1. Hospital slab calculation:
   Given: Floor area = 1,200 m², Slab thickness = 0.15 m, Concrete density = 2,400 kg/m³

Volume of slab:$$ \text{Volume} = \text{Area} \times \text{Thickness} = 1,200 \times 0.15 = 180\, m^3 $$

Mass of concrete:$$ \text{Mass} = \text{Volume} \times \text{Density} = 180 \times 2,400 = 432,000\, kg $$

Answer: Volume = 180 m³; Mass = 432,000 kg

1. Drainage pipe calculation:
   Given: Diameter = 300 mm = 0.3 m, Length = 50 m

Internal cross-sectional area:$$ A = \pi r^2 = \pi \times (0.15)^2 \approx 0.0707\, m^2 $$

Volume when full:$$ V = A \times \text{Length} = 0.0707 \times 50 = 3.535\, m^3 $$

Answer: Area = 0.0707 m²; Volume = 3.535 m³

1. Electrical wiring cost:
   Given: Length = 800 m, Cost per meter = Ksh 250

Total cost:$$ \text{Total Cost} = 800 \times 250 = 200,000\, Ksh $$

Answer: Ksh 200,000

Chapter Summary

This chapter covered the essential steps involved in preparing tender documents for construction projects. It began with the preparation of working drawings, which provide detailed visual instructions necessary for accurate project execution. The chapter then explored work specifications that define the quality and standards required for materials and workmanship. Next, it discussed the bill of quantities, a detailed itemized list that quantifies materials and labor needed for the project. The preparation of the schedule of rates followed, outlining the unit costs for various construction activities. Attention was given to the preparation of conditions of contract, which establish the legal framework and obligations of the parties involved. The chapter also examined forms of agreement, formalizing the contractual relationship between the client and contractor. Finally, it addressed forms of tender, which are the documents contractors submit to offer their bids for the project.