Masonry Magazine May 2001 Page. 11
Figure 1 FIELD FACTORS AND NATIONAL SURVEY RESULTS
(Average, Minimum and Maximum Percentages of Productivity Loss)
| No. | Field Factors | Estimated Percentage of Productivity Loss (%), If the Factor Is... (0% to 100% in each column) |
|---|---|---|---|---|
| | | Minor | Moderate | Severe |
| 1 | Congestion: Change prohibits use of optimum crew size including physically limited working space and material storage. | 6 0-25 | 13 2-35 | 26 5-65 |
| 2 | Morale and Attitude: Change involves excessive inspection, multiple change orders and rework, schedule disruption, or poor site conditions. | 5 0-28 | 13 0-35 | 22 0-70 |
| 3 | Labor Reassignment: Change demands rescheduling or expediting, and results in lost time to move out/in. | 5 0-15 | 12 2-40 | 22 2-65 |
| 4 | Crew Size Change: Change increases or decreases the optimum crew size resulting in inefficiency or workflow disruption. | 5 0-25 | 12 3-50 | 21 5-80 |
| 5 | Added Operations: Change disrupts ongoing work due to concurrent operations. | 5 0-20 | 12 2-50 | 22 4-70 |
| 6 | Diverted Supervision: Change causes distraction of supervision to analyze and plan changed work, stop and re-plan ongoing work, or reschedule work | 6 0-30 | 13 2-40 | 25 5-75 |
| 7 | Learning Curve: Change causes workers to lost time while becoming familiar with and adjusting to new work or a new environment. | 5 0-20 | 12 2-35 | 20 4-70 |
| 8 | Errors and Omissions: Change causes lost time due to mistakes engendered by changed circumstances. | 5 0-15 | 11 2-40 | 21 4-75 |
| 9 | Beneficial Occupancy: Change requires the use of premises by owner prior to work completion, restricted work access, or working in close proximity to owner's personnel or equipment. | 7 0-20 | 14 0-45 | 26 1-75 |
| 10 | Joint Occupancy: Change requires work to be done while other trades not anticipated in the bid occupy the same area. | 7 0-20 | 14 0-35 | 26 4-70 |
| 11 | Site Access: Change requires physically inconvenient access to work area, inadequate workspace, remote materials storage, or poor man-lift management. | 8 0-25 | 15 0-40 | 20 0-75 |
| 12 | Logistics: Change involves unsatisfactory supply of materials by owner or general contractor, causing inability to control material procurement, and delivery and re-handling of substituted materials. | 8 0-20 | 16 0-40 | 27 0-72 |
| 13 | Fatigue: Change involves unusual physical exertion causing lost time when original plan resumes. | 6 0-20 | 12 1-40 | 21 4-80 |
| 14 | Work Sequence: Change causes lost time due to changes in other contractors' work. | 6 0-20 | 14 0-35 | 25 5-70 |
| 15 | Overtime: Change requires overtime causing physical fatigue and poor mental attitude. | 7 0-20 | 15 0-50 | 26 3-80 |
| 16 | Weather or Environment: Change involves work in very cold or hot weather, during high humidity or in a dusty or noisy environment. | 6 0-20 | 13 0-50 | 24 2-100 |
the mason contractor (from E), and 2) 200 hours of unexplained man-hours probably to be absorbed by the mason contractor. The actual man-hours required for the masonry work is 1,200 hours (from F).
Sample 1: To prospectively estimate the lost man-hours due to field factors
Before or during the masonry construction, the estimator figures the total estimated man-hours at 1,000 hours, and moderate congestion and moderate labor reassignment are expected. The expected man-hours lost and total predicted man-hours required for the work can be determined as follow.
A. Total estimated masonry man-hours 1,000 hours
B. Field factors (from Figure 1)
No. 1 Congestion (Moderate) 13%
No. 3 Labor Reassignment (Moderate) 12%
Total %PL 25% (or 0.25)
C. Expected man-hours lost due to the anticipated field factors (AxB) = 1,000 x 0.25 = 250 hours
D. Total predicted man-hours required to perform the work (A+C) = 1,000 + 250 = 1,250 hours
Sample 2: To retrospectively estimate the lost man-hours due to field factors
After completion of the masonry work, the estimator determines that the actual man-hours equals 1,500 hours and the original estimated man-hours was 1,000 hours. During the masonry construction, moderate congestion and moderate labor reassignment were present. The lost man-hours can be determined as follow.
A. Total estimated masonry man-hours 1,000 hours
B. Total actual masonry man-hours 1,500 hours
C. Total lost man-hours (B-A) = 1,500 - 1,000 = 500 hours
D. Field factors (from Figure 1)
No. 1 Congestion (Moderate) 13%
No. 3 Labor Reassignment (Moderate) 12%
Total %PL 25% (or 0.25)
E. Man-hours lost due to the field factors [B-B/(1+D)] = 1,500-[1,500/(1+0.25)] = 300 hours
F. Man-hours lost due to unexplained conditions (C-E) = 500 - 300 = 200 hours
G. Total man-hours required to perform the work (B-E) = 1,500 - 300 = 1,200 hours (more on page 29)