Construction Drawing
What the exam tests
Construction Drawing tests your ability to read and extract information from plans, sections, elevations, details and schedules. You must understand projection, scale, levels, grids, dimensioning, reinforcement notation, hatching and revision control, and relate drawings to specification and measurement.
Core rules
- Orthographic projection shows a three-dimensional object in related views. In first-angle projection the object lies between the observer and the projection plane; in third-angle projection the plane lies between observer and object. The symbol on the drawing identifies the convention.
- Plans are horizontal cuts or views; sections show a vertical cut; elevations show external faces. Levels are usually given in metres relative to a datum, not as scaled dimensions.
- Scale is drawing length : real length. At 1:50, 1 mm on the drawing represents 50 mm real. Never scale work where a written dimension is given; written dimensions govern.
- Gridlines locate structure; setting-out dimensions should be taken from grids or fixed datum lines, not from finished faces unless stated.
- Reinforcement is shown by bar mark, diameter, spacing and shape; schedules give cutting lengths and quantities.
- Revision clouds, revision triangles and issue status must be checked before construction.
Worked example
A plan is drawn at 1:50. A distance on the drawing measures 84 mm between two gridlines. What is the real distance? Real length = drawing length × scale denominator = 84 mm × 50 = 4200 mm = 4.20 m. If the drawing also carries a written dimension of 4200 mm, the dimension confirms the scaled value. If the measured value were 85 mm, the correct action would be to use 4200 mm, not 4.25 m, because written dimensions control over scaling.
Traps
Applying the scale twice; measuring in millimetres but reporting metres without conversion; using a photocopy or PDF print where scale is no longer reliable; confusing first-angle and third-angle symbols; ignoring revision clouds or superseded drawings; and taking dimensions from the wrong face or grid.