Home/Interview questions/Scaffold engineer
Scaffold engineer interview questions and answers
Numbers and checks an engineer must answer without notes, from load ratings to tie plans, quantities and crew output, then the design scenarios interview panels like to ask.
Technical questions
Q1What is the medium duty rating in CSM II-2?
- 120 kg/m² (25 psf)
- 180 kg/m² (37 psf)
- 240 kg/m² (50 psf)
- 360 kg/m² (75 psf)
Answer: 240 kg/m² (50 psf). Light duty 120 kg/m² (25 psf), medium duty 240 kg/m² (50 psf); above that is special duty. CSM II-2 (July 2026) 2.5.1. Verify against the latest edition.
From the free Scaffold Engineer exam.
Q2Scaffold components must carry which load without failure?
- D + L
- D + 2L
- D + 4L
- 4D + L
Answer: D + 4L. Components: dead load plus 4 × the live load; posts: 4 × all gravity loads. The factor is a design margin, not spare capacity. CSM II-2 2.5.1; GI 8.001 §4.22.5. Verify against the latest edition.
From the free Scaffold Engineer exam.
Q3210 tubes of 6.4 m at 4.37 kg/m: what do they weigh?
- 2,750 kg
- 4,590 kg
- 5,873 kg
- 8,880 kg
Answer: 5,873 kg. 210 × 6.4 = 1,344 m × 4.37 kg/m = 5,873 kg. Steel tube 48.3 × 4.0 mm, as used in the AL-YASSIN Engineer course. Verify against the latest edition.
From the free Scaffold Engineer exam.
Q4A scaffold's tie plan shows 22 ties on one façade, of which 13 are reveal ties, each carrying 2.8 kN. Does the arrangement fall within TG20 guidance?
- Yes: reveal ties carry light-duty loads up to 3.5 kN, and 2.8 kN is below that
- No: 59 % of the ties are reveal ties, above the recommended 50 %, so at most 11 should be
- Yes: up to 60 % of ties may be reveal ties if they are checked weekly
- No: reveal ties may never carry more than 2.0 kN each
Answer: No: 59 % of the ties are reveal ties, above the recommended 50 %, so at most 11 should be. 13/22 = 59 %. TG20 recommends that no more than 50 % of the ties to a façade are reveal ties (at most 11 here), and that they are used only where light-duty ties suffice. Relying mainly on reveal ties needs careful consideration, a written procedure and defined responsibility for maintaining their tightness, since they depend on friction. NASC TG20:13 Design Guide, section 2.1.9.9 (verify against TG20:21).
From the free Scaffold Design Engineer (EN/TG20) exam.
Q5A TG20-compliant tower has a 2.7 m × 3.3 m base. What maximum heights do TG20's compliant designs allow when it is (i) internal and (ii) external under a wind management system?
- (i) 10.8 m; (ii) 8.0 m
- (i) 10.8 m; (ii) 8.1 m
- (i) 10.8 m; (ii) 10.8 m
- (i) 13.2 m; (ii) 9.9 m
Answer: (i) 10.8 m; (ii) 8.0 m. Internal: 4 × lesser base (4×2.7 = 10.8 m), not above 10.8 m, so 10.8 m. External: 3 × lesser base (3×2.7 = 8.1 m), not above 8.0 m, so 8.0 m. 8.1 m misses the cap; 13.2/9.9 m uses the larger base dimension. NASC TG20:13 Design Guide, sections 2.5.3 and 2.5.4 (verify against TG20:21).
From the free Scaffold Design Engineer (EN/TG20) exam.
Q6A loose base jack is 760 mm long. Under BS EN 12812, what minimum length of the jack must sit inside the tube?
- 150 mm
- 190 mm
- 228 mm
- 380 mm
Answer: 190 mm. The overlap must be the greater of 25% of the jack length and 150 mm: 0.25 × 760 = 190 mm, which exceeds 150 mm, so 190 mm governs. 150 mm is only the lower bound; 228 mm (30%) and 380 mm (half the jack) are not the rule. Short overlap increases the angular imperfection at the joint. BS EN 12812:2004 7.3.2, 9.3.2.1 (verify against BS EN 12812:2008).
From the free Formwork & Falsework Design Engineer exam.
Q7Birdcage 18 × 12 m to a 9.5 m working platform with a 3 × 3 m vessel inside, full height. The BOQ deducts voids over 10 m³. Net volume?
- 1,966.5 m³
- 2,052.0 m³
- 2,137.5 m³
- 2,173.5 m³
Answer: 1,966.5 m³. Gross 18 × 12 × 9.5 = 2,052.0 m³; void 3 × 3 × 9.5 = 85.5 m³ (over 10 m³, so deduct); net 1,966.5 m³. Method of measurement practice, AL-YASSIN Estimating course. Verify against the latest edition.
From the free Scaffold Estimating, Pricing & Tenders exam.
Q8How is a circular tank scaffold usually measured?
- m³ of the tank
- m² on the outer line of standards × height
- linear metres of guardrail
- number of lifts
Answer: m² on the outer line of standards × height. Developed length on the outer line of standards × height, as the BOQ preamble says. Method of measurement practice, AL-YASSIN Estimating course. Verify against the latest edition.
From the free Scaffold Estimating, Pricing & Tenders exam.
Q9600 m³ of scaffold at 6 m³ per productive scaffolder per shift. Crew of 6 with one non-productive chargehand, 25% lost time. Whole shifts needed?
- 17
- 22
- 27
- 34
Answer: 27. 5 productive × 6 m³ × 0.75 = 22.5 m³ per shift; 600 ÷ 22.5 = 26.7 → 27 shifts. Example data, AL-YASSIN Operations course. Verify against the latest edition.
From the free Scaffold Operations Management exam.
Design scenarios
Q10How do you decide whether a scaffold needs a specific design?
A strong answer covers:
- Is it inside a standard configuration (a TG20 sheet, a system maker's tables)? If not, it needs a design.
- Height, loading class, sheeting, cantilevers, bridges, suspended or special scaffolds.
- The project rules: what the client calls a special scaffold and who must approve it.
Q11Which loads go into a scaffold design?
A strong answer covers:
- Self-weight, the service load class and any concentrated loads.
- Wind in service and out of service, made worse by sheeting or netting.
- Hoisting and impact where they apply, then the load combinations and factors of the code you design to.
Q12How do you check a tie and its anchor?
A strong answer covers:
- Tie duty from the design, not from habit.
- Anchor type suited to the base material, with its rated capacity.
- Pull tests where the anchor depends on the substrate, recorded before the scaffold is loaded.
Q13How do you check the ground under a scaffold?
A strong answer covers:
- Leg load from the design, spread through base plate and sole board.
- Compare the bearing pressure with what the ground can take; ask for ground data when unsure.
- Watch for backfill, voids, slopes and nearby excavations.
Q14A value-engineering idea saves 15% of the material but cuts the safety margin. What do you do?
A strong answer covers:
- Separate real savings (better bay layout, fewer lifts, the right system) from cutting capacity.
- Run the check; the design factors are not spare capacity.
- Put the decision and the numbers in writing.
Tip: Show you can save money without spending the safety margin. That is the engineer they want.
About you
Q15Tell me about a design that had to change on site.
A strong answer covers:
- What changed on site and how you found out.
- How fast you re-checked and what you issued.
- What you now do earlier to avoid it.
Technical answers come from the AL-YASSIN question banks, with the document each one is based on; verify against the latest edition and the rules of the project you are applying to. Scenario answers are practice guidance, not a script. AL-YASSIN is independent and not endorsed by Saudi Aramco, OSHA, BSI or NASC.
How to answer the "tell me about a time" questions
Use four short parts: the situation (where, what scaffold, how high), the task (what you had to decide), the action (what you did, in order) and the result (what changed, with a number if you have one: days saved, findings closed, zero incidents on that job). Keep it under two minutes. Interviewers in this trade listen for one thing above all: that you stop the job when it is not safe, and then find a way to finish it.
Hiring? Check before the interview
Ask candidates for their AL-YASSIN certificate number and check it in seconds, or send a free screening link to a shortlist.
More
Questions
What is asked in a scaffold engineer interview?
Load ratings and design factors, wind and sheeting, ties and anchors, foundations, when a specific design is needed, quantities (m³, m², lm) and crew productivity, plus how you handle changes on site.
Do scaffold engineer exams on AL-YASSIN need a degree?
The role exams are for civil and mechanical engineers, so the certificate is issued after a degree or SCE check. The international exams (EN/TG20 design, formwork and falsework) are open to everyone.