A 10 minute task completed in overtime would only take 6 minutes if it was done the following morning
Some of my previous articles have described the fatigue curve the workforce experiences throughout the day. This has allowed us to find the optimum number of breaks in a day or best duration for a total shift, all to maximise productivity and efficiency. What I would like to talk about here is the value of overtime. If productivity reduces dramatically after 1500 hrs, then what is the efficiency of an additional hour or two immediately after the shift is supposed to have ended?
The figure above represents the productivity through the day for about 200 dry lining fixers and about 50,000 hours of data. This shift has been optimised and is using a 2-break shift pattern. It is quite clear to see the reduction in output at 540 minutes (9 hours) and the subsequent low performance from 9-10.5 hours. This is clearly something more than a continuation of the fatigue curve since there is such a noticeable drop off. There are likely a number of mechanisms at play here including a short break, fatigue and the end of the day being so close, workers are likely not going to ramp to the higher levels seen earlier in the day.
Regardless of the reasons behind the reduction, the important element in this phenomenon is the reduction in output. There is a 40% drop off meaning a 10 minute task completed in overtime would only take 6 minutes if it was done the following morning. Now there are 2 sides to this argument, if you are trying to gain on schedule and you will incur significant costs if you don’t hit a milestone then additional overtime at this poor rate is a good call (providing the penalty is less than the cost of the premium labour).
If the supervisors have the authority to add overtime to ensure their work fronts are complete and they then receive the kudos then this is likely an expensive way to progress the project. Often work-days are tracked in the program and work-hours are used in cost control. This is often a source of unexplained budget overrun, number of burnt days is on-track but costs are high…
So what are the alternatives to running overtime after 1700? We have found that the productivity on a Saturday is a couple of percent higher compared to the Monday to Friday normal hours. One answer could be focusing your overtime at the weekend.
We don’t believe there are inherent reasons why Saturdays are better than week days, more likely the individuals selected for overtime are the more experienced and those selected for overtime during the week are likely the ones who didn’t complete their work in the time expected.
The conclusion to this is make sure your overtime during the week is controlled and you are not using this unnecessarily. Also create a ‘qualification’ system for overtime on Saturdays. This is a great opportunity to make the most of your best people.
If you would like to learn how to improve your productivity in construction and translate these numbers directly onto your bottom line then please get in touch.