3. Building Working Drawings

Introduction to Working Drawings In civil engineering, after the conceptual planning and submission drawings of a building are approved, working drawings are prepared. These are the detailed, finalized sets of drawings used for actual implementation and construction on the site. They provide all necessary dimensions, specifications, and structural details required by engineers and contractors to execute the work.

1. Core Components of a Working Drawing

A complete set of working drawings for a building (whether a single-story load-bearing structure or a multi-story framed structure) typically includes the following comprehensive components:

  • Developed Plan: A detailed floor plan showing exact room dimensions, wall thicknesses, and the precise locations of all doors, windows, and staircases.
  • Elevation: The external architectural face of the building, displaying the overall height, window positions, and structural projections like chajjas (weather shades) and balconies.
  • Section: A vertical cut-through of the building—often passing through critical areas like the staircase or WC/bath—showing internal vertical dimensions such as foundation depth, sill height, lintel height, ceiling height, and slab thickness.
  • Foundation Plan: A dedicated layout showing the excavation details, footing dimensions, and placement of columns or load-bearing walls at the base level.

2. Reading Structural Details in Working Drawings

Depending on the type of structure, an engineer must read and interpret specific details from the working drawings before construction begins:

A. Load-Bearing Structures For structures where walls bear the load of the building, the drawings must be read to identify:

  • The depth and width of the foundation trenches for the walls.
  • The exact thickness of the masonry walls and the materials used for construction.
  • The height and width of all door and window openings.
  • Vertical structural levels, including sill height, lintel height, ceiling height, and floor thickness.
  • Thickness of secondary walls like compound walls, parapets, and partition walls.

B. Framed Structures For reinforced cement concrete (R.C.C) framed structures (columns, beams, and slabs), the drawings will additionally specify:

  • The number, sizes, and layout of all R.C.C columns.
  • The types, sizes, and depths of the isolated or combined footings.
  • The sizes and positions of all plinth beams and floor beams.
  • Detailed reinforcement layouts (steel bars) for slabs, columns, beams, and footings.

3. Essential Schedules and Construction Notes

Working drawings are incomplete without text-based tables and specifications that guide the material quality and component sizing:

  • Schedule of Openings: A table detailing the type, dimensions, and specifications of every door (D), window (W), and ventilator (V) in the building. For example, it might specify a "Single Shutter Panelled Door" made of teak wood with specific rail dimensions.
  • Construction Notes and Specifications: Written instructions that dictate the quality and mix of materials. Common specifications include:
    • Foundation and Plinth: E.g., 1st class brickwork in 1:6 cement mortar over 1:4:8 cement concrete.
    • Damp Proof Course (DPC): E.g., 20mm thick cement concrete (1:1.5:3) mixed with water-proofing compounds.
    • Superstructure and Roofing: E.g., details on floor finishes (like 40mm thick cement concrete) and roof slab thicknesses.

4. Standard Line Conventions in Drafting

To avoid confusion on site, working drawings strictly follow Bureau of Indian Standards (BIS) conventions for different types of lines:

  • Visible Outlines: Thick, continuous lines (0.60 mm to 1.30 mm) used to draw the main features and boundaries of the building.
  • Hidden Lines: Dashed lines evenly spaced (0.4 mm to 0.5 mm thick) used to represent hidden elements like R.C.C chajjas, lofts, or underground foundations that are not visible on the direct surface.
  • Centre Lines: Long and short dashed lines (usually in a 4:1 or 6:1 ratio) used to denote the center of columns, walls, or circular features.
  • Dimension and Extension Lines: Thin, continuous lines used to clearly state measurements. Extension lines start slightly away (2mm) from the object to prevent overlapping with the visible outlines.

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