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Five Common Mistakes In Earthwork Estimating

When I was asked how to avoid mistakes in estimating and take-off, I asked myself what defines a mistake?

Mistakes to me are items such as Scale, Elevation, Drawing, Omission, and Scope of Work errors.

All of these can be avoided by turning your estimating and take-off’s into a structured and organized process. If you are doing Estimates at 2 AM, on software you don’t understand, for a site you have no knowledge of; you will make a “Mistake” eventually.

How do we avoid these common mistakes by organization?

SCALE: Back when Draftsmen used an actual Scale to make the Print these types of errors were not as common. Since the widespread use of CAD and PDF’s we have been subjected to the introduction of error on many levels. At creation of the Drawing it can be an inattentive or inexperienced Engineer. When replication of the Drawing is by an equally inattentive or inexperienced office clerk or Estimator the improper use of Scale has become the most common mistake I have seen.

Avoiding Scale errors requires 3 things, Verification, Verification and Verification.

As mentioned before this error can be made at any level. From the creation of the file to the printing or onscreen take-off, the simple failure to verify scale is a major error.

Sometimes it’s a more insidious error such as an old plotter that reproduces correctly on one axis and incorrectly on the other or an incorrect scale displayed on the page! The only way to confirm is to verify and verify to confirm.

Before moving on it is important to mention improper use of scale. In other words can you be accurate at 1″=100? If you are using a digitizer to measure, the average accuracy is about 1/20th of an inch. That’s 5 FEET on a 100 scale drawing. Can the drawing be blown up to 1″=50 or even 1″=30 and still fit on your digitizer? If so then do yourself a favor, make a record set that is enlarged and confirmed and then use it.

Elevation: Typically a Large numerical error will show up in even a casual check of a computer take-off. The most common elevation mistake in surveying is 1 foot. An isolated error of 1 foot is insignificant on a major take-off. A 1 foot error over a large area can be devastating, causing the import or export of large amounts of material. The best way to confirm the existing topo and the quality of the layout is to use your EW cut/fill image and check the first stakes out in the field. Ask the Engineer to give you a Building corners or Catch Basins with the elevation and cut fill to Finish grade. Take a picture of this and all other stakes before stripping the topsoil! By comparing this with the EW take-off you will at least have a leg to stand on when requesting a change order. Resolve this mistake before proceeding or be willing to live with it.

Drawing: I have already touched on Scale and Numerical Errors on Drawings. Lets look at the error’s such as the Building that isn’t shown, the plan’s that call out Plastic pipe when the spec’s require Concrete pipe, or the use of an outdated topo drawing when the site has undergone significant changes.

A complete review of the specs may save your Company. Boring logs if not included should be requested. If you use the wrong material on a job and get it in the ground you may be subject to reduced payment at the least and removal and replacement with Spec. materials at the worst!

Site visit’s will reduce your liability and also give you in-site into traffic patterns at the site and weight restrictions on roads nearby. Google Earth or Microsoft Virtual Earth are great if the pictures are up to date but are you willing to bet the farm on them?

Omission: Nothing gives you that sick feeling in your stomach like realizing you forgot something in a bid. Maybe it was something like the office trailer but it could be Compaction of fills or another major Item!

Using a preformatted template or at least a checklist of major items helps reduce this error. Try to build the job in your head and remember, Men and Equipment cost money. The next time you forget to allow for a Tie-in to existing utilities or the hardware to lower a water line around a Sewer line remember, Penny’s make Dollars and Minutes make Hours.

Scope of Work: Understanding your responsibilities on a job is vital to the successful execution of the project. Improper assignment of responsibility for tasks can lead to in-efficiency in execution, (ever wait for the power company to move a pole?)

Check and confirm with other contractors you are bidding in conjunction with. EXCLUSIONS or what you are not responsible for are at least as important as what you are doing!

There are five mistakes that I’ve seen all too often. I have no funny stories to tell about them because mistakes are rarely funny.

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