Chapter 12 Exercises

Work these with a calculator and a blank sheet, not by scrolling back to the chapter. Estimating is a performance skill; reading about it produces the feeling of competence and not the competence. Where a calculation exercise has a numeric answer, it is hidden in a <details> block — resist it until you have your own number. Selected full solutions appear in Appendix J.

Difficulty legend: ⭐ basic · ⭐⭐ applied · ⭐⭐⭐ advanced judgment · ⭐⭐⭐⭐ extension / research

Part A — Conceptual Understanding ⭐

A1. In one sentence each, define direct cost, general requirements, and general conditions, and give an example of each from the Northgate Outpatient Pavilion. Then explain why moving a cost between the second and third categories is not merely a bookkeeping decision.

A2. The chapter's threshold concept states that an estimate is "a priced bundle of assumptions, quantities, and risks." Rewrite that idea in your own words, then explain what it implies about how you should judge whether an estimate was good — given that you will not know the actual cost for two years.

A3. Explain, without arithmetic, why formwork quantity has almost nothing to do with concrete quantity. Then name two design changes that would increase concrete volume while leaving formwork essentially unchanged, and two that would do the reverse.

A4. What is the difference between bank, loose, and compacted cubic yards? Which one appears on a grading plan, which one appears on a hauling invoice, and which one appears on a compaction test report?

A5. List the components of a fully burdened labor rate in the order they are built up. Which of them are computed on the base wage, which on the base wage plus vacation accrual, and which on the wage-plus-fringes subtotal? Why does the distinction matter?

A6. Why is workers' compensation cost different for the same worker doing different work? Name one pair of trades whose comp rates you would expect to differ substantially, and explain what an experience modification rate does to both.

A7. State the difference between markup and margin in one sentence each, and write both conversion formulas from memory.

A8. Why does Kestrel build an independent in-house estimate for major trades it does not self-perform? Give two distinct reasons — one about the bid you are submitting, and one about the job you will be building.

A9. What is a basis of estimate, and what are its six sections? Which section is most often omitted, and what does its absence cost you when the project goes into dispute?

A10. Distinguish a qualified bid from a hidden-exclusion bid. State the one-sentence test from the chapter, and explain why the same exclusion can be professional on one procurement and disqualifying on another.

Part B — Applied Analysis ⭐⭐

B1. A junior estimator hands you a takeoff sheet reading:

   Slab on grade ............. 33,000
   Foundation walls .......... 620
   Footings .................. 1,240
   Rebar ..................... 261,560

List everything wrong with this sheet before you look at a single number for accuracy. There are at least four defects. Then rewrite two of the lines the way they should appear.

B2. Your model-based quantity extraction reports 18,614.37 LF of interior partition. Your hand takeoff of the same drawings reports 18,600 LF. Which number do you carry, and what do you write next to it? Then explain, in three sentences, what would have to be true about the model before you would trust its gypsum board quantity as well as its length.

B3. A subcontractor's quote for underground plumbing is $412,000 and reads, in the last paragraph of page two: "Excludes trench excavation and backfill, spoil removal, dewatering, sheeting and shoring, and rock." Your estimate assumed the plumbing sub carried their own trench. Estimate the magnitude of the exposure using the chapter's §12.7.4 pipe unit cost as a starting point, and describe the three things you do before the bid is submitted.

B4. Kestrel's historical database says a crew hangs 1,050 SF of metal-stud partition per crew-day. You are pricing a scope that will be built on the fourth floor, in a building with one hoist, while two other trades work the same corridor, on a 50-hour-per-week schedule. Using the adjustment table in §12.8.2, propose a rate, then write the basis-of-estimate note that must accompany it. Be explicit about how you combined the factors and why the combination is approximate.

B5. Northgate's structural steel is 985 tons erected. A fabricator's quote says "965 tons." List five questions you ask before you conclude the quote is 20 tons light. What documents would settle each question?

B6. Your estimate's general conditions were built on a 565-calendar-day schedule at $5,150/CD. Two weeks before bid, the design team issues a bulletin adding a mechanical penthouse that the scheduler says adds 40 calendar days. The estimator adds the penthouse's direct cost and nothing else. What did they miss, what is it worth, and what does this tell you about the sequence in which an estimate and a schedule should be produced?

B7. An estimator applies a 5% waste factor to the drywall quantity and uses a unit price from a supplier who "already includes waste." Quantify the error on Northgate's 412,000 SF at $0.42/SF material, then propose a company policy — one sentence — that makes the error structurally impossible.

B8. You have two competing conceptual checks on your detailed concrete estimate: $/CY of concrete and $/SF of building. Northgate is 132,000 SF with 2,370 CY of foundation concrete. Explain what each check is good at detecting and what each will miss entirely.

Part C — Calculations and Deliverables ⭐⭐–⭐⭐⭐

C1. Volume conversions. Compute each, showing the conversion:

(a) A slab 28,400 SF at 6 inches thick. CY? (b) A footing 9'-6" × 9'-6" × 2'-9". CY each; CY for 17 of them? (c) A grade beam 24 inches wide × 36 inches deep × 480 LF. CY? (d) An asphalt lot of 41,500 SF. SY? (e) 1,340 tons of stone, quoted at €/tonne by an import supplier. How many tonnes?

C2. Earthwork with swell and shrinkage. A site has 68,000 BCY of cut and requires 19,000 CCY of compacted embankment. Soil is common earth: swell 24%, shrinkage 13%.

(a) How many BCY of cut must be retained to produce the required embankment? (b) How many BCY are exported? (c) How many LCY is that in trucks? (d) At $17.25/LCY hauled and dumped, what is the export cost? (e) What would you have bid if you had extended the export BCY directly at $17.25? By how much would you have been wrong?

C3. Build a burdened rate. An ironworker's base wage is $41.00/hr. Fringes: health and welfare $5.60/hr; retirement 5.0% of base; vacation accrual 6.0% of base. Payroll taxes 10.55% of (base + vacation). Workers' comp manual rate $21.40 per $100 with an EMR of 0.91, applied to (base + vacation). General liability 1.90% of (base + vacation). Small tools 2.0% of wage-plus-fringes.

(a) Build the rate line by line. (b) What is the burden factor? (c) Compare it to the carpenter's 1.484 factor from the chapter, and state in one sentence what accounts for nearly all of the difference.

   Base                                              $41.00
   Health and welfare                                 $5.60
   Retirement    5.0% × 41.00                         $2.05
   Vacation      6.0% × 41.00                         $2.46
   Wage + fringes                                    $51.11
   Taxable base = 41.00 + 2.46                     = $43.46
   Payroll taxes 10.55% × 43.46                       $4.59
   Workers' comp 21.40% × 0.91 = 19.474% × 43.46      $8.46
   General liab.  1.90% × 43.46                       $0.83
   Small tools    2.00% × 51.11                       $1.02
   BURDENED                                          $66.01

C4. Build a unit cost. Price one square foot of 8-inch CMU wall, laid and grouted.

Crew: 1 foreman at $48.00 base, 3 masons at $39.00 base, 2 mason tenders at $27.00 base. Use the chapter's fringe and burden schedule (§ 📋 Try it), with workers' comp at 10.20% for all classifications on this scope. Production: 340 SF of wall per 8-hour crew-day. Material: block $3.42/SF; mortar $0.38/SF; grout and reinforcing $0.71/SF; waste 4% on block and mortar; sales tax 7.25% on all material. Equipment: mast-climbing scaffold and mixer allocated at $395/day.

(a) Burdened crew cost per hour. (b) Cost per day. (c) Unit cost per SF. (d) Total for 14,800 SF. (e) What happens to the unit cost if the wall is on the fourth floor and you apply a 0.90 height factor?

C5. Formwork takeoff. Take off the formwork, in SFCA, for the following foundation elements:

• 340 LF of foundation wall, 12 inches thick, 9'-0" tall, formed both faces.
• 22 pier caps, 5'-0" × 5'-0" × 2'-6".
• 6 elevator pit walls, 12 inches thick, 8'-0" tall, forming a rectangle 9'-0" × 7'-0" inside dimension, formed both faces.
• 1,240 LF of slab-on-grade edge form at 6 inches.

Then compute the concrete volume of the first two items and calculate the SFCA-per-CY ratio for each. Explain the ratios in one sentence.

C6. Markup and margin. Your direct cost is $3,840,000. Indirects add $611,000.

(a) What price yields a 9.5% margin? (b) What markup percentage is that? (c) If you instead apply a 9.5% markup, what margin do you actually earn, and how many dollars of profit did you leave behind? (d) Now add a bond at an effective 1.28% of the final price, using the divisor method. What is the final bid, and what is your margin on the final bid?

C7. Derived quantity — build it and break it. Using the chapter's §12.10.3 derivation of Northgate's 412,000 SF of gypsum board:

(a) Recompute the total if the weighted average partition height is 11'-0" instead of 10'-6". (b) Recompute it if the opening-deduction convention changes from "over 50 SF" to "over 100 SF," which halves the deduction. (c) State the dollar impact of each at an installed board cost of $2.85/SF. (d) Write the two basis-of-estimate sentences that would let a reviewer catch both assumptions in under a minute.

Part D — Judgment and Ethics ⭐⭐⭐

D1. Your estimate is complete at $18,240,000. Your VP of Operations says the number "needs to start with a seventeen" to be competitive, and asks you to find $300,000. Describe three legitimate ways to move the number and three illegitimate ways. For each legitimate one, say what new risk it creates and who now owns that risk. For each illegitimate one, say who eventually pays.

D2. You discover, four days before bid, that a scope item — perimeter blocking for the millwork — appears on the architectural details but in no specification section and in no trade's likely scope. You could: (a) issue a pre-bid RFI, which alerts every competitor; (b) price it quietly and carry the cost; (c) exclude it in a bid qualification; (d) say nothing and write a change order later. Evaluate all four against the procurement type — first as a public hard bid, then as a negotiated CM-at-Risk selection. Does your answer change? Why?

D3. A subcontractor calls at 1:40 p.m. on bid day: "I think I'm light on the mechanical. Are you using me?" You are, and you know their number is roughly $340,000 below the next bidder. What do you say, what do you carry, and what do you document? Consider the bid-shopping line discussed in Chapter 15 and Chapter 16, and be specific about what makes a conversation legitimate versus not.

D4. Your firm's historical productivity database is excellent — and it was built entirely on open-shop private work. You are bidding a prevailing-wage public job for the first time in six years. What do you do about your production rates, and what do you write in the basis of estimate? Note that the wage determination changes the cost of an hour; the exercise is about whether it changes the number of hours, and how you would find out.

D5. An estimator on your team consistently comes in 4–6% high and consistently wins nothing. Another comes in 3–5% low and wins everything, and their jobs consistently finish at 1.5% below the estimate on cost but with a large volume of contested change orders. Which one has the more serious problem? Defend your answer using the threshold concept from §12.2.

Part M — Mixed and Interleaved Practice ⭐⭐–⭐⭐⭐

M1. (Chapters 7 + 12.) You are taking off a partition scope. The floor plan shows a wall type tag "B2." The partition schedule on A-601 defines B2 as 3⅝" studs at 16" o.c. with one layer of ⅝" board each side. Specification section 09 21 16 requires two layers of ⅝" board on all walls enclosing imaging rooms. The imaging rooms are tagged B2. Which document governs, what quantity do you carry, and what do you do about the conflict? Reference the order-of-precedence framework from Chapter 7.

M2. (Chapters 6 + 12.) Build a five-line contingency justification for a $2,000,000 concrete package: five named risks, an estimated probability and impact for each, and the resulting contingency dollar amount. Then answer: is your contingency a percentage, or is it a sum of priced risks? Which does Chapter 6 say it should be?

M3. (Chapters 8 + 12.) Northgate's mass excavation is 44,000 BCY of cut. Using the equipment concepts from Chapter 8 and the export arithmetic from §12.4.1, estimate: (a) the number of 14-LCY truckloads to export 32,000 BCY; (b) at 4.5 loads per truck per day, the number of truck-days; (c) at 22 trucks on site, the number of working days of hauling; (d) one sentence on what that duration does to the schedule and therefore to general conditions.

M4. (Chapters 11 + 12.) Your conceptual estimate from Chapter 11 priced the Willow Street structure at a $/SF rate. Your detailed takeoff now produces a number 14% higher. List six possible causes, ranked by how likely each is, and describe the single reconciliation step that would distinguish among them.

M5. (Chapters 12 + 14.) You are given a $5,000,000 direct-cost estimate and a 14-month schedule. The owner asks what happens to the price if they compress the schedule to 11 months. Identify every line on the §12.9.1 estimate summary that changes, say which direction each moves, and explain why the answer is not simply "general conditions go down by three months."

M6. (Chapters 12 + 20 + 28.) Your month-6 cost report shows concrete formwork at 4,180 SFCA installed against 812 crew-hours. Compute the achieved production rate. Compare it to the 58.125 SFCA/crew-hr used in the estimate. Then state the three things you do with that finding — one for this job, one for the next estimate, and one for the company database. Reference Chapter 20 and Chapter 28.

Part E — Research and Extension ⭐⭐⭐⭐

E1. Find the real numbers. Identify your own jurisdiction's treatment of sales and use tax on construction materials — whether the contractor is treated as the consumer of materials, whether public work is exempt, and whether an exemption certificate process exists. Then find your state's workers' compensation rating bureau and identify how manual class-code rates are published. Write a one-page memo of what an estimator in your market must know before carrying a material cost or a burdened labor rate. Cite the actual agencies; do not rely on secondary summaries.

E2. Take off a real drawing. Obtain a real set of construction documents — many public agencies post bid documents publicly, and many university facilities departments will share an old set. Take off one complete scope: all concrete, or all interior partitions, or all underground utility. Record the sheet and detail source for every quantity. Then write the basis-of-quantities page. Estimate how long the takeoff took you, divide the quantity by the hours, and you now have your first personal productivity datum — about estimating, which is a production activity like any other.

E3. Interview a working estimator. Ask three questions: Where do your production rates come from? What is the last thing you missed, and how did you find out? What does your basis-of-estimate document look like? Write up what surprised you. Pay particular attention to whether the answer to the third question is "we don't really have one" — and, if so, ask what happens when a job goes into a change-order dispute.