CTE & TRADES · POSTSECONDARY CTE, APPRENTICESHIP, COLLEGE · 50-60 MINUTES
The Slab Takeoff: Concrete, Vapor Retarder and Rebar Quantities lesson plan
Construction-management and estimating students walk a full-size slab, then take off concrete with thickened edges and waste, vapor retarder with laps, and rebar with splices and offcuts.
On this page: Teach it in 5 steps · Learner card · Printable
At a glance
Time: 50-60 minutes
Level: Postsecondary CTE, apprenticeship, college
Subject: CTE & trades: Concrete, Vapor Retarder and Rebar Quantities
Grouping: Teams of 3.
Space: A 24 ft x 32 ft area (a gym or hallway); or work from the 1:1 print at a smaller scale table if space is short.
Included: Teacher script, scenario sheet, learner sheet, exit ticket and answer key with every number worked
Open the printable lesson: script, scenario, learner sheet and answer key (PDF) →
Teach it in 5 steps
The whole lesson on one screen. Details for each step are further down.
Before class: Tape the 24 ft x 32 ft outline (or roll out the print).
Hook (0-5 min): Walk the outline with the class. "This is 768 square feet. How much concrete?"
Measure (5-10 min): Teams verify the outline, band and strip with tapes. They compare with the scenario sheet.
Main work (10-50 min): Work through the procedure below: Concrete → Vapor retarder → Rebar.
Check (50-55 min): Exit ticket: A 10 ft x 10 ft slab is 4 in thick. How many cubic yards before waste?
Learner card
Read this with your crew, or print it for each team.
Your challenge
The supplier needs an order tonight: how many yards, how many rolls, how many bars? Too little stops the pour; too much is money on the ground.
By the end, I can:
compute concrete volume for a slab with thickened edges and convert to cubic yards
lay out vapor-retarder strips with laps and count rolls and tape
count rebar for a grid with cover, splices and reused offcuts
Who uses this
estimators, project engineers and superintendents, who turn drawings into orders before every pour.
Essential question
How do you turn a slab drawing into an order that is neither short nor wasteful?
What learners learn and show
The big idea: A takeoff breaks the slab into simple solids, converts to purchase units, and adds the allowances real installations need: waste, laps and splices.
Show it: a takeoff sheet with concrete in cubic yards and the order quantity, vapor retarder strips, rolls and tape, and rebar counts with and without offcut reuse.
Objectives
Compute slab, thickened-edge and strip volumes and total them in cubic yards.
Add waste and round to the supplier's increment.
Plan vapor-retarder strips with 6-in laps and count rolls and seam tape.
Count #4 bars at 18 in each way and compare a naive and an optimized stock order.
Materials and prep
A 1:1 print of a 24 ft x 32 ft slab plan, or its outline taped on the floor with the thickened edge and interior strip marked
Tape measures, calculators
The printable: scenario sheet and takeoff sheet
Prep
Tape the 24 ft x 32 ft outline (or roll out the print). Mark a 12-in band inside the perimeter (thickened edge) and a 16-in strip across the slab, 22 ft long, between the bands (interior bearing strip).
Print the scenario sheet and one takeoff sheet per team.
Space: A 24 ft x 32 ft area (a gym or hallway); or work from the 1:1 print at a smaller scale table if space is short.
Grouping: Teams of 3.
Lesson procedure
0-5 min, Hook: Walk the outline with the class. "This is 768 square feet. How much concrete?" Ask: What is wrong with just multiplying by 4 inches? Listen for: The thickened edge and the strip hold more concrete; waste is real.
5-10 min, Measure: Teams verify the outline, band and strip with tapes. They compare with the scenario sheet. Ask: Which dimensions did you actually measure? Listen for: Outline, band width, strip length and width.
10-25 min, Concrete: Teams compute the slab, the extra depth under the band, and the extra under the strip; total; convert to cubic yards; add 5% waste; round up to the supplier's 1/4-yard increment. Ask: Why add the band as extra depth only? Listen for: The top 4 in is already in the slab volume.
25-35 min, Vapor retarder: Teams lay out 10-ft-wide strips running the 32-ft way with 6-in side laps, then count rolls (10 ft x 100 ft) and seam tape. Ask: Why do laps change the count? Listen for: Each lap loses 6 in of coverage.
35-50 min, Rebar: Teams count #4 bars at 18 in each way with 3-in cover, then order 20-ft stock with 24-in lap splices: first naively (two bars per run), then reusing offcuts. Ask: How many bars did reusing offcuts save? Listen for: The optimized order is much smaller; see the key.
50-55 min, Exit ticket: Individual exit ticket.
Checks for understanding
Ask: Why convert to cubic yards before adding waste? Look for: Either order works; the point is to round only once, at the end, to the supplier's increment.
Ask: Why is the bar count "spaces + 1"? Look for: A row of bars has one more bar than gaps between them.
Ask: When do laps matter for the vapor retarder? Look for: Whenever strips meet: every seam loses the lap width.
Exit ticket
A 10 ft x 10 ft slab is 4 in thick. How many cubic yards before waste? Answer: 1.23 cu yd (33.33 cu ft / 27).
Strips are 10 ft wide with 6-in laps. How many strips cover a 19-ft width? Answer: 2 strips cover 19.5 ft; 2 is enough.
Bars at 12 in on center across 10 ft with 3-in cover at each edge. How many bars? Answer: 10 bars (114 in / 12 = 9 full spaces, + 1).
Scoring: 1 point each, plus 1 for showing units. 3 or more = secure.
Common misconceptions
Learners may think: Volume is area x thickness, done. Address it: Thickened edges, strips and waste add real yards; take each solid separately.
Learners may think: Order exactly what you computed. Address it: Concrete comes in increments and short loads cost extra; always round up to the increment after waste.
Supports and extensions
Give the unit-conversion card: 1 cu yd = 27 cu ft; 4 in = 0.333 ft; 8 in = 0.667 ft; 16 in = 1.333 ft.
Multilingual learners: label slab, band, strip, lap and splice on the floor with pictures.
Extension: price the order with local unit prices and add a pump or short-load fee.
Transfer task: Take off the slab on a real set of foundation drawings, or the Big Floor Plans Trades Bay sample plan.
Ready to teach it?
The printable has the teacher script, the scenario sheet, the learner sheet and the answer key. Open the printable lesson →
Need the floor plan itself? Get a 1:1 print quote.
Paying for the print? Use a grant
Many teachers fund the 1:1 print with Perkins V career and technical education funds. Start from From Drawing to Takeoff: a construction-trades pathway on life-size plans, our grades 9-12 CTE grant packet, and add this lesson to its timetable. The packet has a project description, measurable objectives, a lesson timetable, an evaluation plan, a budget and a principal letter, written to the questions funders ask.
Download the grant packet (PDF) · Editable Word version · All funding options
Why at full scale
Walking the outline first makes the solids visible: the band and the strip are taped on the floor, so learners see why the 4-in slab is not the whole volume.
Codes, standards and frameworks
Perkins V (CTE): postsecondary and secondary CTE program context
Vapor retarder laps: manufacturer instructions based on ASTM E1643 call for side and end laps of at least 6 in, taped; follow the project specification
Codes and standards change and are adopted locally. This lesson teaches the method; use the edition your jurisdiction or program has adopted.
Related lessons
The Finish Takeoff · Estimating & Takeoffs, Grades 9-12, CTE
Price per Square Foot, On Foot · Real Estate & Business, Grades 9-12
Hang the Board · Drywall Takeoff & Seam Planning, Grades 9-12, CTE
More in the College & Trades track: The MacLeamy Curve · The Pre-Pour Walk · Square the Layout · Receptacle Layout to Code · Measure It Like an Appraiser