Building Drawing
What the domain tests
Building Drawing tests reading and producing orthographic drawings: plans, elevations, sections, details, symbols, scales, dimensioning, line conventions and schedules.
Core rules
- Orthographic projection: front elevation, with the plan below in first-angle or above in third-angle. Check the title block and symbol before reading.
- Scale 1:50 means one unit on paper represents 50 units in reality. Convert millimetres to metres after multiplying.
- Line types: continuous thick for outlines, thin for dimensions and hatching, dashed for hidden detail, chain for centrelines.
- Building dimensions are normally in millimetres unless stated otherwise. Read figured dimensions; do not scale off the drawing.
- Symbols include door swing, window, level marker, section marker and north point.
Worked example
A wall measures 84 mm on a 1:50 plan. Real length = 84 x 50 = 4200 mm = 4.2 m. A door shown as 900 mm wide should measure 900/50 = 18 mm on paper. A 230 mm wall should be 4.6 mm. Reasoning: multiply by the scale denominator, then convert units.
Traps
- Treating 1:50 as 50 mm equals 1 m; the ratio is unitless.
- Scaling a dimension that is already written on the drawing.
- Mixing plan and elevation views.
- Omitting hidden lines for openings or services.
- Forgetting to check the revision number.