Building drawings are essential documents in the quantity surveying profession, serving as the primary source of information for measurement, cost estimation, and project planning. Producing accurate scaled drawings ensures clear communication between architects, engineers, contractors, and quantity surveyors. This chapter focuses on the conventions of signs and symbols, dimensioning techniques, and the use of scales in building drawings, all critical for precise interpretation and preparation of tender documents and bills of quantities.

2.1 Signs and symbols in building drawings

In Kenya’s construction industry, understanding the standard signs and symbols used in building drawings is fundamental for quantity surveyors to interpret drawings correctly and quantify materials accurately. These symbols convey complex information about building elements without lengthy descriptions, improving clarity and reducing errors. This section covers the types of lines used, dimensioning practices, and the importance of standard symbols in building drawings.

2.1.1 Lines used in building drawings

Lines in building drawings are visual tools that communicate specific information about the structure, elements, and construction details. Quantity surveyors must distinguish between line types to interpret drawings correctly and extract precise measurements.

1. Continuous Thick Lines
   These lines represent visible edges or outlines of objects in a drawing. They are the most prominent and indicate the physical boundaries of walls, doors, windows, and other architectural features.

2. Continuous Thin Lines
   Used for dimension lines, projection lines, hatching, and short center lines. They provide supplementary information without overwhelming the primary outlines.

3. Dashed Lines
   Represent hidden features that are not directly visible, such as beams or pipes behind walls. Quantity surveyors must recognize these to account for concealed elements during measurement.

4. Chain Lines (Long Dash and Short Dash)
   Indicate centre lines of objects or symmetry axes. These lines are critical in identifying the geometric relationships of building components.

5. Phantom Lines (Long Dash and Two Short Dashes)
   Show alternate positions of movable parts or adjacent structures. Quantity surveyors use these to understand potential changes or additions during construction.

6. Break Lines
   Used to indicate that a section of the drawing is omitted for clarity or space. This helps focus on important details without unnecessary repetition.

2.1.2 Dimensioning

Dimensioning in building drawings provides the exact measurements necessary for construction and quantity takeoff. Accurate dimensioning is vital for quantity surveyors to prepare correct cost estimates and avoid costly mistakes.

1. Types of Dimensions

   • Linear dimensions specify lengths, widths, and heights.
   • Angular dimensions indicate angles between components.
   • Radial dimensions are used for circles and arcs, specifying radii or diameters.

2. Dimension Lines and Extension Lines
   Dimension lines are thin continuous lines terminated by arrowheads or ticks, showing the distance measured. Extension lines extend from the feature to the dimension line without touching the object outline.

3. Placement and Clarity
   Dimensions should be placed outside the object outline to avoid clutter. They must be clearly readable, with sufficient spacing to prevent confusion.

4. Units and Notation
   In Kenya, metric units (millimeters and meters) are standard. Dimensions must be clearly marked with units or understood from the drawing scale.

5. Chain Dimensioning vs. Baseline Dimensioning
   Chain dimensioning adds dimensions sequentially along a line, which can accumulate errors. Baseline dimensioning references all measurements from a single datum point, reducing cumulative inaccuracies.

6. Tolerance Indication
   Dimensioning may include tolerances to specify allowable deviations, critical for precise fitting of components and for cost implications in quantity surveying.

Chapter Summary

This chapter has provided a comprehensive overview of producing scaled building drawings, beginning with the essential signs and symbols used in such drawings, including the various line types and the principles of dimensioning to ensure clarity and accuracy. It then covered the different scales commonly applied in building drawings, enabling precise representation of structures. Detailed guidance was given on creating floor plans that show the layout of spaces, followed by instructions for drafting roof plans that illustrate the design and slope of roofing elements. The chapter also explained how to develop building elevations to depict the external appearance and vertical dimensions of the structure, as well as building sections that reveal internal construction details through cut-through views. Finally, it introduced the application of Computer Aided Design software, focusing on AutoCAD and ArchiCAD, highlighting their roles in enhancing the efficiency and accuracy of modern building drawing production.