Site overhead of 20 unclaimed wet days, as a share of contract value

What it is. 0.35% of contract value at the low end (0.81% at the high end): the time-related site overhead that keeps running on 20 wet days no one claims an extension or delay costs for.

Range 0.35% to 0.81% (scenario)

Sample. A worked calculation, not a measurement. The time-related share of preliminaries comes from 30 senior Australian estimators; the working days and the 20 wet days are the ones Transport for NSW builds into its own daywork labour rate for major civil contracts.

What it is not. A WORKED EXAMPLE, NOT A MEASUREMENT. The 20 wet days a year that Transport for NSW estimates are priced into the rates, so their overhead is paid for; this is the cost of the same number of days going unclaimed beyond the allowance. How many unclaimed wet days a real job loses is not measured anywhere we found. The 10% to 20% preliminaries figure is a UK 2002 number read second-hand, and the estimators' survey was mostly building work. Use your own preliminaries rate and wet-day count if you have them.

Our arithmetic. Low end: 10% preliminaries x 45.49% time-related / 261 week days a year x 20 days = 0.35% of contract value. High end: 20% x 45.49% / 226 working days x 20 days = 0.81%. The contract value cancels, so the share holds for any job size. 45.49% is O'Leary and Vaz-Serra table 6; 10% to 20% is their introduction, citing Chan and Pasquire 2002; 261, 226 and 20 are Transport for NSW TS 01566 Table E2.1.

Where it came from

• O'Leary & Vaz-Serra (2025), Challenges in pricing preliminaries costs for contractors: An Australian case study
  introduction citing Chan & Pasquire 2002; table 6 (30 Australian estimators) · source record
• Transport for NSW (2024), QA Specification TS 01566 (G2-C2): General Requirements (Major Contracts)
  Annexure G2-C2/E, Table E2.1, rows c, h and i · source record

claim_window/weather_unclaimed_days_share_of_contract · AU, AU-NSW · F, F42 ·the record ·link to this figure ·dispute this figure(or email support@demiton.io)