Prefabrication: material cost vs. labor cost

    I was trying to come up with a formula for masonry contractors of how to quantify in dollars how utilizing prefabricated brick arches saves money.  Like a profit & loss statement there are fixed numbers and numbers that can manipulated.  We are doing a job right now for LFJ masonry called Watkins MOB in Virginia.  We have prefabricated and delivered 86 brick arches.  Eusebio Cantone of LFJ told me that when they estimated the project they added the price of the arches to the material costs and subtracted estimated production time in hours from their take-off.  He said:

     "The largest benefit is that we can set these and keep going, we don't have to wait! At the end of the day you can figure the total time you took to fabricate the arches (man-hours) and that would be your time savings on the project. Based on crew size and number of arches on the project you could also determine the following, the project saved X number of man-hours to fabricate and set arches therefore saving X number of days on the total project and that is where equipment savings comes in as well."

I figured we used 8 diamond blades, cut over 8000 brick, purchased, cut and bent 3500 feet of #4 epoxy coated rebar, 20 boxes of wall ties, and purchased and mixed 800 bags of cement/grout.  We also dedicated 2 employees to work on this project for 100 days each.  This does not take into account utilities, fuel, transportation, and maintenance.  Other costs that are sometimes overlooked by contractors that are reduced by installing prefabricated arches are rental equipment, employee insurance and liability.

So here is the math that gives you more profit:

$ INCOME

- $ ARCHWAY SYSTEM PREFAB

= X

+ $ SAVED IN LABOR HOURS 

+ PRODUCTIVITY ( $ FROM DAYS ON SITE)

+ MATERIAL NOT PURCHASED (REBAR, CEMENT, WALL TIES, ETC.)

+ EMPLOYEE LIABILITY

+ EFFICIENCY (ON TIME DELIVERY, START THE NEXT JOB SOONER)

+ RENTAL COSTS AND MAINTENANCE FEES SAVED

= MORE $$$$$$$$$$$

The hardest thing to put into the equation is efficiency...lets say LFJ masonry finished this project 20 work days ahead of schedule, how do we add a dollar amount to the equation.  In reality that same masonry crew can complete more jobs in a given year, therefore increasing revenue.  I think efficiency would be a % that carries over to the revenue for the year on the profit/loss statement.  

Thanks Seb.  When I take some pictures of the finished buildings I will be sure to post them.