Building Drawing and Reading of Drawings
What this domain tests
You must read a plan, elevation and section, apply the correct scale, recognise line types and symbols, and extract dimensions a site team can work to.
Core rules and concepts
- Scale: site plans 1:1000 to 1:5000; building plans usually 1:100 or 1:50; details at 1:20, 1:10 or 1:5. A plan drawn at 1:100 shows 1 mm for every 100 mm on the ground.
- Line types: continuous thick for visible outlines and cut surfaces, dashed for hidden work, chain-dotted for centre lines and section cutting planes, thin continuous for dimension and extension lines.
- A plan is a horizontal section taken about 1.2 m above floor level, so doors and windows both show. Elevation shows the outside face; section shows the cut with floor levels and heights.
- Conventions: dimensions in millimetres, levels in metres, north arrow, title block, door and window symbols, electrical and plumbing symbols, staircase arrow showing the up direction.
- Standard sizes: 230 mm wall, 900 × 2100 mm door, 1200 × 1200 mm window, stair riser 150 mm and tread 300 mm in ordinary buildings.
Worked example
A staircase in a 3.0 m floor-to-floor building with 150 mm risers. Number of risers = 3000 ÷ 150 = 20. Number of treads is one less than the risers = 19, so the going length = 19 × 300 = 5700 mm, which needs a mid-landing. Writing both the count and the reasoning is the expected answer.
Similarly, a wall measured 46 mm on a 1:100 print is 46 × 100 = 4600 mm = 4.6 m on site.
Traps that cost marks
Forgetting to multiply by the scale factor; treating a section as an elevation; using the tread count as equal to the riser count; dimensioning in metres on a plan; missing the door swing or north arrow in a drawing exercise.