Measurement of building works begins with accurate interpretation of working drawings and precise taking off of quantities for all building elements. In the Kenyan building industry, this process is critical for preparing reliable estimates and cost plans that guide project budgeting and tendering. Mastery of measurement techniques ensures that quantities reflect the true scope of work, facilitating efficient procurement and construction management.

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1.1 Interpretation of working drawings

Working drawings are the set of scaled, dimensioned and annotated drawings that show exactly what is to be built, where, how big and of what materials, and interpreting them means reading and understanding this information correctly so that the work can be set out, priced and built as the designer intended. Every trade on site, from the foreman setting out foundations to the plumber fixing pipes, depends on the drawings, so a misread dimension, level or symbol can lead to costly demolition, delays and disputes. In practice, the reader studies the title block and drawing list, understands the scale and conventions, relates plans, elevations and sections to each other, and checks dimensions, levels and notes before starting work. Example: before setting out a new dormitory for a secondary school in Kericho, the site supervisor cross-checked the foundation plan against the ground floor plan and noticed that a column grid line was dimensioned differently on the two drawings, and the architect's correction saved the contractor from casting a misplaced column base.

Tools and Equipment for Reading Drawings

Types of Working Drawings

Elements of a Working Drawing

• Title block: Shows the project name, client, drawing title, drawing number, scale, date, designer and approval signatures, usually at the bottom right of the sheet.
• Revision block: Lists changes made to the drawing with revision letters, dates and descriptions, so the reader knows the drawing is current.
• Scale: States the ratio between drawing size and real size, which must be read before measuring anything.
• North point: Shows the orientation of the building on the site, important for setting out and sun shading.
• Grid lines: Lettered and numbered reference lines, usually through column centres, used to locate elements accurately.
• Dimensions: Figures showing lengths, widths and positions, usually in millimetres on building drawings.
• Levels: Heights of floors, ground, foundations and roofs relative to a datum, usually in metres.
• Annotations and notes: Written information on materials, specifications, mixes and construction methods.
• Symbols and hatching: Standard graphic signs for doors, windows, fittings and materials such as brickwork, concrete and earth.
• Legend or key: Explains symbols, line types and abbreviations used on the drawing.

Types of Lines Used on Drawings

Common Symbols and Abbreviations

• Door symbol: An opening in a wall with a line and arc showing the door leaf and the direction it swings.
• Window symbol: Thin parallel lines within the wall thickness, showing the frame and glass.
• Stair symbol: Parallel lines for treads with an arrow showing the direction going up, often marked "UP".
• Sanitary fittings: Simple outlines for WC, basin, shower tray, sink and bath at their positions in the plan.
• FFL: Finished floor level, the level of the top of the floor finish.
• NGL and FGL: Natural ground level before work and finished ground level after landscaping.
• DPC and DPM: Damp proof course in walls and damp proof membrane under floor slabs.
• RC and BRC: Reinforced concrete and steel welded mesh fabric.
• Dia or Ø: Diameter of a bar, pipe or circular element, such as Y12 for a 12 mm high-yield bar.
• TOW and SFL: Top of wall and structural floor level.

Steps to Interpret Working Drawings

1. Check the drawing register: Confirm you have the complete set of drawings and that each is the latest approved revision.
2. Read the title block: Note the project, drawing title, number, scale, units and date before looking at the details.
3. Study the legend and general notes: Learn the symbols, abbreviations, line types and general specifications used.
4. Orient the drawing: Use the north point and grid lines to understand where the building sits and how the drawings relate to the site.
5. Read the plans: Identify rooms, wall thicknesses, openings, fittings and overall and internal dimensions.
6. Relate plans to elevations and sections: Follow section lines on the plan to the section drawings, and match elevations to the plan to understand heights and vertical construction.
7. Read dimensions and levels: Use written dimensions rather than scaling wherever possible, and check that strings of dimensions add up to overall dimensions.
8. Study details and schedules: Refer to enlarged details and door, window and finishes schedules for exact construction and materials.
9. Cross-check between drawings: Compare architectural, structural and services drawings to identify clashes or inconsistencies.
10. Raise queries in writing: Report any errors, missing information or conflicts to the architect or engineer and obtain written answers before proceeding.

Calculations from Working Drawings

Converting a Scaled Measurement to Real Size

Example: on a 1:100 floor plan of a SACCO office in Embu, a room width measures 45 mm with a scale rule.

Real length = Measured length × Scale factor

Real length = 45 mm × 100

Real length = 4,500 mm

Real length = 4.5 m

Finding the Area of a Room from Dimensions

Example: a banking hall on the plans of a bank branch in Nakuru is dimensioned 12,500 mm by 8,400 mm.

Area = Length × Width

Area = 12.5 m × 8.4 m

Area = 105 m²

Finding a Height Difference from Levels

Example: the section of a clinic at a county referral hospital in Machakos shows FFL +1.250 m and NGL +0.800 m.

Height of plinth = FFL − NGL

Height of plinth = 1.250 m − 0.800 m

Height of plinth = 0.450 m (450 mm)

Common Errors in Interpreting Drawings

• Using an old revision: Working from a superseded drawing leads to building elements that no longer match the design.
• Scaling instead of reading dimensions: Paper copies may shrink or be printed at the wrong size, so written dimensions must be used where given.
• Confusing units: Building dimensions are usually in millimetres and levels in metres, and mixing them causes large errors.
• Misreading the scale: Measuring a 1:50 drawing with the 1:100 edge of the scale rule doubles or halves sizes.
• Ignoring notes and details: Important information on materials, cover to reinforcement and fixing methods is often in notes rather than on the main drawing.
• Not cross-checking drawings: Failing to compare architectural and structural drawings can cause clashes, such as a beam blocking a door opening.
• Wrong orientation: Reading a drawing upside down or ignoring the north point can lead to mirror-image setting out. Example: a building contractor in Thika avoided setting out a hotel kitchen block back to front when the foreman checked the north point and grid lines against the site plan before pegging the corners.

Chapter Summary

This chapter covers the essential skills for measuring building works, starting with the interpretation of working drawings to understand project specifications accurately. It then explains the systematic process of taking off quantities for various building elements including the substructure, superstructure, doors, windows, finishes, and internal and external fittings. The working up process is described as a method to organize and verify measurements before proceeding. Abstracting is introduced as the step where measurements are compiled and categorized for further use. The preparation of billing papers is detailed, comparing the Direct Billing method with the Cut and Shuffle technique to ensure accurate documentation. Finally, the chapter outlines the compilation of bills of quantities, discussing different formats such as Operational, Elemental, Trade, Activity, and Annotated Bills, each serving specific purposes in construction cost management. This comprehensive approach equips students with practical knowledge for precise measurement and cost estimation in building projects.