When asked how to avoid errors in estimation and takeoff, I wondered what defines an error?
Errors for me are items such as scale, elevation, drawing, omission, and scope of work errors.
All of this can be avoided by turning your estimates and takeoffs into a structured and organized process. If you’re doing Estimates at 2 AM, in software you don’t understand, for a site you don’t know about; eventually you will make a “Mistake”.
How do we avoid these common mistakes by the organization?
SCALE: Back when artists used a true scale to print, these kinds of mistakes weren’t as common. Since the widespread use of CAD and PDF, we have been subject to the introduction of errors on many levels. In the creation of the Drawing it can be a distracted or inexperienced Engineer. When Drawing replication is done by an equally distracted or inexperienced office worker or Estimator, improper use of Scale has become the most common mistake I’ve ever seen.
Avoiding scaling errors requires 3 things, Check, Check and Check.
As mentioned before, this mistake can be made at any level. From file creation to print to screen take-off, simply not checking for scale is a big mistake.
Sometimes it’s a more insidious error, like an old plotter playing correctly on one axis and incorrectly on the other, or an incorrect scale displaying on the page! The only way to confirm is to check and check to confirm.
Before continuing, it is important to mention the inappropriate use of the scale. In other words, can you be accurate to 1″ = 100? If you’re using a digitizer to measure, the average accuracy is about 1/20 of an inch. That’s 5 FEET on a 100 scale drawing. Can you enlarge the drawing to 1″=50 or even 1″=30 and still fit on your digitizer? If so, do yourself a favor and make an extended and confirmed recordset and then use it.
Elevation: A large numerical error will usually show up even in a casual check of a computer takeoff. The most common elevation error in surveying is 1 foot. An isolated error of 1 foot is negligible on a major takeoff. A 1 foot error over a large area can be devastating, causing large amounts of material to be imported or exported. The best way to confirm existing topography and design quality is to use your EW Cut/Fill image and verify early stakeouts in the field. Have the engineer provide building corners or catchments with elevation and cut fill to finish grade. Take a picture of this and all other stakes before removing the topsoil! Comparing this to the EW takeoff, at least you’ll have a leg to lean on when you ask for a change order. Please resolve this error before continuing or be willing to live with it.
Drawing: I have already touched on scale and numerical errors in drawings. Let’s look at errors such as the building not being shown, the plans indicating plastic pipe when the specifications call for concrete pipe, or the use of an out-of-date survey drawing when the site has undergone significant changes.
A complete revision of the specifications can save your company. Boring records should be requested if they are not included. If you use the wrong material on a job and bury it, you may be subject to a reduced payout at a minimum and removal and replacement with Spec. materials at worst!
Site visits will reduce your liability and also provide you with site traffic patterns and weight restrictions on nearby roads. Google Earth or Microsoft Virtual Earth are great if the images are up to date, but are you willing to gamble everything on them?
Omission: Nothing gives you that sick feeling in your stomach like realizing you forgot something on an offer. Maybe it was something like the trailer for the office, but it could be Fill Compaction or another major item!
Using a pre-formatted template or at least a checklist of the main elements helps to reduce this error. Try to build the work in your head and remember, Men and Equipment cost money. The next time you forget to allow a connection to existing utilities or the hardware to drop a water line around a sewer line, remember that Penny’s makes dollars and minutes make hours.
Scope of Work: Understanding your responsibilities in a job is vital to the successful execution of the project. Improperly assigning responsibility for tasks can lead to inefficiency in execution (ever waited for the power company to move a pole?)
Check and confirm with other contractors you are bidding on jointly with. EXCLUSIONS or what you are not responsible for are at least as important as what you are doing!
There are five errors that I have seen too often. I don’t have funny stories to tell about them because mistakes are rarely funny.