Ask ten estimators how long it takes to pull one metre of NYM-J 3×2.5 mm² and you will get answers between 1.5 and 3 minutes. They are all right. The answer depends on the site.
The number that changes the answer is the productivity coefficient — a scalar between roughly 0.7 and 3.0 that multiplies the base hours. Most bids we have looked at treat this coefficient as a single gut-feel number written into a corner of the Excel: "×1.15 for foreign project" or "×1.4 for hospital site". That is not wrong, but it is fragile.
The version that survives audit is the 12-factor decomposition. Each factor has a fixed weight and a small set of named choices with multipliers:
- Building type × 0.10 (shell-and-core = 0.85, hotel = 1.10)
- Height × 0.10 (single-storey = 0.80, 16+ floors = 1.25)
- Climate × 0.07 (mild = 1.00, extreme = 1.25)
- Employer difficulty × 0.10 (standard = 1.00, extreme = 3.00)
- Quality regime × 0.15 (light = 0.90, extreme = 3.00)
- … and so on.
Summed, weight × value gives the overall coefficient. It is exactly the same mental model estimators already carry — but it is now visible, auditable, and reproducible from one bid to the next.
Which matters, because the coefficient is the single biggest lever between "we won the bid at 15% margin" and "we won the bid at 3% margin and it hurts until the last invoice."