How to Calculate Winter Construction Inefficiency

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If not properly planned and accounted for, winter construction inefficiency will result in unexpected project delays and added costs. While no de facto standard exists which models inefficiency caused by winter conditions, a research-based procedure was developed by the Society of American Military Engineers and the Department of Defense in 1986. This model factors in cold temperature, wind speed and snowfall into the overall construction efficiency.

Estimate the number of manual labor hours needed for the project during winter construction. This is the number of laborer hours that project work would require during normal weather conditions.

Estimate the number of equipment hours needed for the project during winter construction. This is the number of construction equipment hours, such as backhoe work, that project work would require during normal weather conditions.

Determine if the snowfall precipitation expected during the construction period is considered light, moderate or heavy. Look at the historical snowfall data for the project location to predict expected snowfall during the project duration. Light snowfall amounts generally have accumulation of less than 0.4 inches per hour. Moderate snowfall ranges from 0.4 to 0.8 inches per hour. Heavy snowfall is considered as greater than 0.8 inches per hour.

Estimate the expected efficiency level of the manual workforce. If the manual laborers typically are highly motivated with a high efficiency level, then use a "high efficiency" model. If the manual laborers are not typically easily motivated and find reason to complain, then use a "low efficiency" model. The "Effect of Cold Weather on Productivity" report uses a “high efficiency” model for all equipment hours.

Use Figure 6 of the “Effect of Cold Weather on Productivity” paper. Draw a straight line starting at the average cold temperature during the work day on the left side through the average wind speed. Intersect the drawn line with the center inflection line. Draw a straight line from this point through the snowfall intensity level to the line on the right side. Read the value intersected on the right side. This is the expected equipment efficiency factor.

Use either Figure 4 or 5 of the “Effect of Cold Weather on Productivity” paper, based on a high efficiency or lower efficiency workforce chosen in Step 4. Draw a straight line starting at the average cold temperature during the work day on the left side through the average wind speed. Intersect the drawn line with the center inflection line. Draw a straight line from this point through the snowfall intensity level to the line on the right side. Read the value intersected on the right side. This is the expected manual labor efficiency factor.

Add up the total estimated laborer hours from Step 1 and the estimated equipment hours from Step 2. This is the total construction hours required during normal weather conditions.

Multiply the equipment efficiency factor from Step 5 by the total estimated equipment hours from Step 2.

Multiply the manual labor efficiency factor from Step 6 by the total estimated laborer hours from Step 1.

Add the result of Step 8 and Step 9. This sum is the expected number of total equipment and laborer hours required for the project during cold weather conditions. Take this sum and divide it by the total hours during normal weather from Step 9 to determine the inefficiency during cold weather.