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The method for determining whether your estimate should factor in overtime relies on a series of calculations for your project scope, production rate, and crew rate. All of these calculations are flexible based on your materials, type of trade, and how big your crew is.
NOTE: In the following scenario, we use small, round numbers with really rough production rates for the purposes of quick math. Your production rates may vary.
I’m a small general contractor with a 4-man crew rebuilding a garage addition into a bedroom space. My trades are limited to drywall, insulation, wood walls, and carpet. I have 2 weeks to complete the project. Is this enough on 8-hour day straight time?
Using takeoff software or construction estimating services, get a full quantity takeoff of the project’s scope you plan to complete. The end deliverable will be a table with a list of descriptions and quantities.
5/8” Drywall 3,000 SF
R13 insulation 3,000 SF
2x6' Wood Framed Exterior Walls 3,000 SF
Carpet Flooring 2,000 SF
Determine your production rate for each task, in the units of “SF per Manhour,” “LF per Manhour,” etc. This is the amount of material 1 person can install in 1 hour. Include reasonable time for setup and cleanup in a usual shift.
Drywall Install 50 SF/manhour
Insulation 100 SF/manhour
Wood Walls 50 SF/manhour
Carpet Flooring 100 SF/manhour
If you need help figuring this out, think of how many SF of material a 2-man crew or 4-man crew can install in one hour. Then, divide that SF by the crew count to get the SF/manhour.
Divide the quantities by your production rate to get the resulting number of manhours necessary.
Drywall 3,000 / 50 = 60 manhours
Insulation = 3,000 / 100 = 30 manhour
Wood Walls = 3,000 SF / 50 = 60 manhours
Carpet Floor = 2,000 SF / 100 = 20 manhours
Determine your crew size for the jobs duration. This number will vary throughout the jobs duration. Ideally, you’ll want to know the exact crew size for each task to get a true answer. But, for most purposes, you can assume one crew size that’s consistent throughout most of the project.
Divide manhours by crew size to get “crew hours.” Crew hours are the number of hours your crew would be on site.
Crew hours math:
Drywall 60 manhours / 4 crew = 15 crew hours
Insulation 30 manhour / 4 crew = 7.5 crew hours
Wood Walls 60 manhours / 4 crew = 15 crew hours
Carpet Floor 20 manhours / 4 crew = 5 crew hours
Total crew hours = 42.5 hours
Add in “buffer” time for site setup and cleanup.
The production numbers above are usually just installation with minimal cleanup. Give yourself a safety net. For small jobs with a 4-man crew, 1 day of setup and 1 day of cleanup is plenty of time. The hours allotted in these days can be used for material runs, as well.
For this scenario, we'll add 8 crew-hours for setup/layout/planning/material purchases and 8 crew hours for cleanup.
Buffer time math:
42.5 + 8 + 8 = 58.5 crew hours
Calculate how many work days are needed for the task at hand. To do this, divide crew hours by # of hours in your work day. Many crews work 8-hour days, some 7s, some 10s, etc.
Number of Workdays calculation:
58.5 crew hours / 8 hours per day = 7.3 days
Compare to original schedule. We need 7.3 work days to reasonably complete the project scope. We have two weeks (10 work days) to complete the job, so we do not need overtime or double shifts.
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