Plant cost breakdown: Construction expenses are roughly what percentage of the total direct cost of a chemical plant (rule of thumb)?

Introduction / Context:
Estimating a plant's total erected cost involves apportioning direct costs (equipment, installation, piping, instrumentation, buildings) and indirects. Construction expenses are one component within direct costs.

Given Data / Assumptions:

• Typical chemical process facility.
• Order-of-magnitude or study estimate stage.
• Average construction complexity.

Concept / Approach:
Rule-of-thumb fractions are used when detailed quotes are unavailable. Construction expenses (temporary facilities, field supervision, small tools, etc.) are often on the order of ten percent of total direct cost in many estimating guides.

Step-by-Step Solution:
Consult standard breakdowns: construction expenses commonly ~10% of total direct cost.Exclude extremes: 2% is too low; 30–50% would imply unusual site conditions or scope.

Verification / Alternative check:
Cross-check with past projects or estimating handbooks showing construction overheads in the single-digit to low-teens percent range.

Why Other Options Are Wrong:
2% understates typical field costs; 30% and 50% are excessive for ordinary projects.

Common Pitfalls:
Confusing construction expenses (a subset of direct cost) with overall indirect costs or contractor's fee.

Final Answer:
10%