403A Blueprint Reading & Layout 1 — Questions and Answers
Question 1: On a construction drawing, what does the abbreviation 'O.C.' stand for?
- On Centre (Correct answer)
- Outside Corner
- Open Circuit
- Over Clearance
Correct answer: On Centre
'O.C.' stands for 'On Centre', indicating the distance measured from the centre of one structural member to the centre of the next, commonly used for stud, joist, and rafter spacing.
Question 2: Which scale is most commonly used for residential floor plans in Canada?
- 1:50 (Correct answer)
- 1:100
- 1:200
- 1:500
Correct answer: 1:50
A scale of 1:50 is the most common for residential floor plans in Canada, meaning 1 mm on the drawing equals 50 mm in reality. This provides enough detail for construction purposes.
Question 3: What type of line on a blueprint indicates a hidden or concealed feature?
- Dashed line (Correct answer)
- Solid heavy line
- Centre line
- Break line
Correct answer: Dashed line
Dashed or hidden lines represent features that exist but cannot be seen from the current view, such as footings below grade, hidden beams, or structural members concealed within walls.
Question 4: When reading a site plan, the benchmark elevation is marked as 100.000 m. A finished floor elevation is shown as 100.450 m. How high above the benchmark is the finished floor?
- 450 mm (Correct answer)
- 45 mm
- 4.5 m
- 4500 mm
Correct answer: 450 mm
100.450 m minus 100.000 m = 0.450 m, which equals 450 mm. Benchmark readings use metres with three decimal places where the last three digits represent millimetres.
Question 5: What does a section view on a drawing show?
- An interior cut-away view of a building component (Correct answer)
- The roof plan from above
- The exterior elevation of a wall
- The property boundary lines
Correct answer: An interior cut-away view of a building component
A section view shows an imaginary cut through a building or component, revealing interior construction details such as wall assemblies, floor-to-ceiling heights, and how components connect.
Question 6: On a drawing, what does the symbol with a circle and an arrow pointing to a wall indicate?
- A section cut reference (Correct answer)
- A door swing
- A window opening
- A plumbing fixture
Correct answer: A section cut reference
A circle with a letter/number and an arrow indicates a section cut — the arrow shows the direction of view, and the letter/number references the section drawing on another sheet.
403A Blueprint Reading & Layout 1
On a construction drawing, what does the abbreviation 'O.C.' stand for?