One method for tracking labor production for use in estimating future jobs. Another use for this production rate is scheduling the amount of manpower needed for a given activity with a given duration.
Let’s use our previous example of the production rate of .065 hours per lineal foot to install footing formwork. Also given is a total lineal footage of 4000 feet and a duration of 5 days. How many people will I need to install the formwork?
One carpenter, on a 5 day work week, works 8 manhours per day. We can use that to figure the manhours required to install the formwork. Let’s start with the manhours required – 4000 feet multiplied by our production rate of .065 comes up with 260 manhours. In the 5 day duration we have 40 manhours per carpenter. Divide that into 260 manhours required and we come up with 6.5 or 7 carpenters for that week to finish the work on schedule. What happens when we accelerate the schedule and only have 3 days to complete.
There are 2 ways to deal with a schedule acceleration. You can either increase the number of people or the amount of time they work in a day. Back to our example – we still have 260 manhours required to complete the work. If we are not allowing any overtime we will need to increase our workforce. Now each of our carpenters have 24 manhours that they can work. Divide duration of 260 manhours by 24 manhours workable time and we come up with 10.8 or 11 carpenters. What happens when we only have our 7 carpenters available?
Taking the duration of 260 manhours and dividing by 7 carpenters we come up with 37 hours required from each carpenter. Divide that amount by 3 days and we come up with 12.4 hours per day (31.5 total hours of overtime) to complete the activity on time. So how do we decide if we increase the manpower or increase the overtime?
Overtime or Manpower
This is a simple calculation of multiplying the total hours by a straight wage for no overtime – 260 manhours times $17.00 = $4420. With the overtime method we have 228.5 manhours at straight time and 31.5 hours of overtime. 228.5 times $17.00 ($3884.5) plus 31.5 times $17.00 * 1.5 ($803.25) = $4687.75. The difference in labor cost is $267.75. Now we need to ask ourselves a question – is it better for the job to give the overtime or increase the manpower?
In my opinion the question comes down to resource leveling. Our goal in scheduling resources is to slowly ramp up our workforce to a peak at the middle of the project and diminish at the end of the project. I believe it to be disruptive to haphazardly increase manpower substantially for a short period of time. In this example it would probably cost me more than $267.75 in office management and other overhead costs to increase the manpower for 3 days. Ultimately it comes down to a management decision on whether or not the increase in cost is acceptable. Another option is to go ahead and extend the schedule for an activity because it would be too costly to bring in more manpower and maybe we can catch up the delay in another activity where we may be able to quickly and cheaply make up the time.