When asked how to avoid errors in estimation and takeoff, I wondered what defines an error?

Errors for me are such things as errors of scale, elevation, drawing, omission, and scope of work.

All of this can be avoided by making your estimates and takeoffs 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 draftsmen used true scale to make the print, these types of errors were not that 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 can be a distracted or inexperienced Engineer. When Drawing replication is done by an equally distracted or inexperienced clerk or Estimator, improper use of Scale has become the most common mistake I have 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 takeoff, simply not checking for scale is a big mistake.

Sometimes it’s a more insidious bug, like an old plotter rendering correctly on one axis and incorrectly on the other, or incorrect scaling displayed on the page! The only way to confirm is to check and check to confirm.

Before continuing, it is important to mention the improper 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 1/20th of an inch. That’s 5 FEET on a 100 scale drawing. enlarge the drawing to 1″=50 or even 1″=30 and it still fits in your digitizer? If so, do yourself a favor, make an enlarged and committed recordset and then use it.

Elevation: A large numerical error will usually show up even on 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. Ask the engineer to provide building corners or catch basins with elevation and cut fill to finished grade. Take a picture of this and all other stakes before you remove the topsoil! Comparing this to the EW takeoff, you’ll at least have a leg to stand on when requesting a change order. Please resolve this error before proceeding 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, plans indicating plastic pipe when the specifications call for concrete pipe, or using an outdated topographical drawing when the site has undergone significant changes.

A complete revision of the specifications can save your company. Boring logs should be requested if not included. If you use the wrong material on a job and bury it, you may be subject to a reduced minimum payment 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 go all out for them?

Omission: Nothing gives you that sick feeling in your stomach like realizing you forgot something on a deal. Maybe it was something like the office trailer, but it could be Backfill Compaction or something else important!

Using a pre-formatted template or at least a checklist of top items helps 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 for a connection to existing utilities or hardware to lower a water line around a sewer line, remember that Penny’s makes dollars and minutes make hours.

Job Scope: Understanding your responsibilities on a job is vital to the successful execution of the project. Incorrect assignment of 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 with. EXCLUSIONS or what you are not responsible for is at least as important as what you are doing!

There are five errors that I have seen too often. I don’t have any funny stories to tell about them because bugs are rarely funny.