Case Study 12-1 — The Three Things Dani Missed

A footing takeoff, corrected line by line, and what each error was actually worth

Setup

Project: Northgate Outpatient Pavilion — 132,000 SF, four stories, CM at Risk, $47,500,000 GMP. Scope: Foundation concrete. 148 spread footings with column pedestals. People: Tomás Reyes, chief estimator, Kestrel Construction Group. Dani Okonkwo, field engineer, three weeks in. Documents in play: S-101 Foundation Plan; S-104 Enlarged Site Entry Plan; S-501 Foundation Details and Schedules (footing schedule at 2/S-501, pedestal schedule and typical detail at 4/S-501).

(Kestrel, Northgate, Meridian Health System, and everyone in this case study are illustrative composites. The numbers are internally consistent and realistic; they are not from a specific real project.)

Tomás handed Dani a printed E-size sheet, an architect's scale, a paper takeoff sheet, and a red pencil, and asked for the footing concrete in cubic yards. Four hours and forty minutes later Dani came back with 1,129 CY. The number in Kestrel's estimate was 1,240 CY.

Nine percent low.

What follows is the reconciliation Tomás walked Dani through. It is reproduced here because the three errors are not exotic. They are the three most common takeoff errors in commercial estimating, and every one of them was made by a careful person who was trying hard.

What Dani did right

Start here, because the failure analysis is worthless if you think the estimator was sloppy.

Dani did four things correctly, and they are the four things beginners usually skip:

1. Found the footing schedule rather than scaling every footing off the plan. Scaled dimensions are approximations; scheduled dimensions are the contract.
2. Built a table by mark — F-1 through F-6 and CF-1 — with volume each, count, and extension, rather than adding footings one at a time in a running total.
3. Red-ticked each footing on the plan as it was counted, so nothing was counted twice.
4. Found the pedestals. The concrete between the top of the footing and the underside of the column base plate is a separate schedule on a separate detail, and missing it entirely is the classic first-takeoff disaster. Dani caught it and priced it.

Dani's sheet was a competent piece of work. It was also $43,000 wrong.

What happened: the three errors

Error 1 — Nine footings on a sheet nobody opened

Dani counted 139 footings. The schedule totals 148.

The missing nine were not hidden. They were on S-104, the enlarged site-entry plan, because the entry canopy and the loading dock were drawn at a larger scale on their own sheet — six F-2 pads under the canopy columns and three CF-1 combined footings at the loading dock.

The diagnostic that would have caught it in four seconds: the schedule listed counts by mark that summed to 148. Dani's plan count was 139. The document told Dani the count was wrong and Dani did not compare the two numbers.

This is Rule 4 from the chapter — measure once, check twice, and make the second check a different method. Counting the plan is one method. Summing the schedule is a different method. Comparing them is free.

What it cost:

Note that the concrete is less than half the cost of the miss. A missed footing is not a missed cubic yard; it is a missed assembly — the dig, the forms, the rebar, the placement, the strip, the backfill. Estimators who price a miss at the material rate under-report their own errors by half.

Error 2 — A line-skip on the schedule

Dani carried F-6 at 3'-6" thick. The schedule says 4'-0". Dani had read across from the F-5 row, one line up.

   Correct:  14.0 ft × 14.0 ft × 4.0 ft = 784.0 CF ÷ 27 = 29.04 CY each
   As read:  14.0 ft × 14.0 ft × 3.5 ft = 686.0 CF ÷ 27 = 25.41 CY each
   Error per footing:                                       3.63 CY
   × 6 footings:                                           21.78 CY

Six inches of thickness on six footings. Almost twenty-two cubic yards.

Why this happens and why it will happen to you. A footing schedule is a wide table with narrow rows. Your eye enters at the mark column on the left and has to travel eight or nine columns to the right to find thickness. On a printed E-size sheet at a plot table, the eye drifts by one row roughly as often as it stays put. Tomás's fix is not "be careful." It is a straightedge — a physical ruler laid under the row being read, moved down one row at a time. On screen, it is the same discipline: highlight the active row.

The general principle is worth stating separately, because it applies well beyond schedules: controls beat intentions. "Be careful" is not a control. A straightedge is a control. A count reconciled against a schedule total is a control. A second person reading the number back is a control. Controls survive fatigue, deadline pressure, and the fourth hour of a takeoff. Intentions do not.

What it cost:

Error 3 — No waste line

Dani's sheet ended with a total and nothing under it. The total was the neat-line geometric volume of the footings and pedestals: 1,216.43 CY.

Nobody pours geometry.

A spread footing is placed into an excavation cut by a machine, against earth, with tolerances measured in inches, not sixteenths. The hole is bigger than the drawing. Concrete spills. The last truck of a pour goes back to the plant with material in the drum that you paid for. Kestrel's historical concrete waste on footings against earth runs 2 to 5 percent depending on soil and crew; on Northgate's soils the estimate carries just under 2 percent.

   Net (neat-line) volume  .................  1,216.43 CY
   Waste and over-excavation allowance (1.9%)   23.57 CY
   ------------------------------------------------------
   CARRIED IN THE ESTIMATE  ................  1,240 CY

What it cost: waste is material only — the crew does not install the waste — so this one is priced at the material rate, not the placed rate:

   23.57 CY × $177.90/CY = $4,193

The subtlety worth catching: applying waste to labor as well would have over-stated the miss. Errors have to be priced correctly in both directions, or your error analysis becomes as unreliable as the estimate it is auditing.

The reconciliation

About $43,000, on one line item, on one sheet, in one trade.

Analysis

The three errors are three different kinds of error

This matters more than the total, because each kind has a different fix.

Only the second one is what people usually mean by "a mistake." The first is a process gap and the third is a knowledge gap, and neither responds to trying harder.

Why "nine percent" was the right reaction

Tomás's first words were "nine percent is a good first takeoff." That was not kindness; it was calibration. A first-time takeoff that lands within ten percent has the method right and the checks missing. A first-time takeoff that lands within one percent usually means the estimator quietly copied a number from somewhere. And a first-time takeoff that is thirty percent off means the structure of the work was not understood at all.

Percentage error is diagnostic. Learn to read it:

What $43,000 actually means at Kestrel

Kestrel's fee on Northgate is $1,804,800 on a $47,500,000 GMP — a 3.80% margin.

   $42,969 ÷ 0.0380 = $1,130,763

Kestrel has to build about $1.13 million of work to earn back what that one takeoff sheet gave away. That is the arithmetic that makes estimators particular, and it is why the correction meeting took ninety minutes on a sheet that took four hours to produce. Checking is cheap. Rebuilding margin is not.

And note what did not happen: nobody was fired, nobody was shamed, and the sheet went back to Dani to redo rather than getting quietly fixed by a senior estimator. An office where the estimator who made the error does not get to see and correct it is an office that will make the error again next year, with a different person, on a bigger job.

The instruction that mattered most

Tomás's last line was not about footings:

"Again. And this time write down every assumption you make, next to the number it belongs to."

Consider what a documented sheet would have done for each error. Error 1: a note reading "count per S-101 = 139; schedule total = 148 — RECONCILE" would have flagged the gap at the moment it appeared, before the sheet ever left the desk. Error 2: a note reading "F-6 thickness 3'-6" per schedule 2/S-501" invites the reviewer to check the schedule — and the reviewer would have found 4'-0" in about five seconds. Error 3: the absence of a waste line is itself visible on a documented sheet, because a documented sheet has a place for one.

Documentation is not a record of the takeoff. It is a mechanism that makes errors visible while they are still cheap. That is the threshold concept from §12.2, expressed as a work habit rather than as a principle.

Discussion Questions

1. Of the three errors, which would be hardest to catch in a digital takeoff, and why? Which would be easiest? Does on-screen takeoff change the risk profile, or just the speed?

2. Error 1 cost $32,102, of which only $15,955 was concrete. Walk through why the "missed assembly" framing produces a truer number than the "missed material" framing — and name one scope on Northgate where the ratio would be even more extreme.

3. Tomás priced the waste error at the material rate rather than the placed rate. Defend that choice. Then construct the one situation where waste does carry a labor cost, and explain where that cost should be captured instead.

4. Kestrel's process caught this because a senior estimator reviewed a junior's work against an existing number. What checks would catch these three errors on a scope where no prior number exists — a first-of-its-kind element, or a job the company has never bid?

5. The chapter argues that "be careful" is not a control. Design three specific, physical or procedural controls — not exhortations — that a two-person estimating department could adopt this week to prevent each of these three error types.

Your Turn

Take the corrected footing schedule from the chapter (§12.4.2) and do the following:

(a) Compute the formwork quantity in SFCA for the F-3 and F-5 footings only. Show perimeter × depth × count.

(b) Suppose the structural engineer issues a bulletin increasing every F-4 footing from 10'-0" square to 11'-0" square, thickness unchanged at 3'-0". Compute the change in concrete CY, the change in formwork SFCA, and the change in reinforcing pounds (at 110 lb/CY). Then price all three at the chapter's unit costs.

(c) Notice something about your answer to (b): the concrete went up 21%, and the formwork went up by a different percentage. Compute both percentages and explain, in two sentences, why they differ.

(d) Write the three-line basis-of-quantities note that should accompany your revised F-4 quantity — number, unit, source, and method — as it would appear on a real takeoff sheet.