Several studies have been undertaken to quantify the possible effects of adverse weather. These studies report widely varying effects and different "ideal" ranges of temperature and humidity. A 1966 study of residential construction found that work was frequently halted due to bad weather. But that no reduction in productivity occurred when conditions were such that work continued in spite of bad weather [Clapp 1966, cited in Yiakoumis (1986)].

This paper presents the most acceptable methods from case law and demonstrates their applications for analyzing the loss of productivity. These methods include earned value analysis, measured mile analysis, and combinations of these two.

The first issue to clarify is whether the loss of productivity was due to the contractor. There are several ‘self inflicted’ causes that this can be attributed to. Productivity will suffer if there is not sufficient supervision to manage the labour force.

In an attempt to isolate the impact of change orders on labor productivity, Ibbs selected “normal” projects where changes and change orders occurred, but without other impacts such as delay, acceleration, trade stacking, learn curve, multiple shifts, bid error, labor force mismanagement, etc. These projects were in the $40 million to $1.2 billion range, and can be described as EPC turnkey contracts with a direct hire labor force working either 4 – 10 hour days or 5 – 8 hour days. Projects with multiple shift and/or overtime work were excluded from the study.

The first issue to clarify is whether the loss of productivity was due to the contractor. There are several ‘self inflicted’ causes that this can be attributed to. Productivity will suffer if there is not sufficient supervision to manage the labour force.

The measured mile approach compares productivity during periods of a project that have been adversely impacted to the productivity levels during periods that were not impacted, or that were unhindered. This unimpacted or unhindered period of performance is referred to as the “Measured Mile”, which is used as the baseline to predict what the contractor’s cost performance should-have-been, or would-have-been.

The total cost approach is probably the most common technique used to demonstrate a loss of productivity due to its simplistic nature and hence quick compilation but for the very same reasons it is also the most rejected of all the techniques used.

One of the most contentious areas in construction claims is the calculation or estimation of lost productivity. Unlike direct costs, lost productivity is often not tracked or cannot be discerned separately and contemporaneously. As a result, both causation and entitlement concerning the recovery of lost productivity are difficult to establish.

“Go back and look at the baseline schedule,” Ibbs suggested. “Look at the staffing on the project. Verify that [the staffing] was reasonable. Look at the sequence. Look at the time periods when the work was going to be done. Look at the pacing of the work, the rhythm of the work, the throughput of the work. Make sure that the original plan was reasonable and [was] a good starting point.”

It is important to use known and accepted industry sources whenever possible to establish and build inefficiency tables. Reliable industry standards, practices, surveys, historical data, and case studies can all prove to be excellent sources for developing a table of factors for labor inefficiency for use in construction planning.