Bidding 24 Classrooms on Night Shifts: Area, Gallons, and Crew Size
A school district solicits a bid to recoat the walls only of 24 identical classrooms. Each room is 30 ft by 32 ft with a 9 ft ceiling. Per room there is one 3 ft by 7 ft door and two windows, each 5 ft by 4 ft. The existing coating is a sound, uniform, light-colored latex eggshell, and the district wants two coats of the same color with no ceiling work. Work may occur only from 4:00 p.m. to midnight, Monday through Friday, and the building must be clean and secured at the end of each shift; realistically seven productive hours per painter per shift. The window is 12 working days. Your production rate for rolling walls, including cut-in at ceiling and base and normal masking, is 350 sq ft per labor-hour per coat. Paint covers 350 sq ft per gallon per coat, costs $135 per 5 gal pail, and burdened painter labor is $42 per hour. The district wants a firm lump sum; the existing coating has passed a tape adhesion test.
1. Compute the wall area, the two-coat quantity, and the material cost, with 10% waste.
Read the worked answer
Perimeter per room: 2 × (30 + 32) = 124 ft. Wall area: 124 × 9 = 1,116 sq ft. Deductions: door 3 × 7 = 21 sq ft; two windows at 5 × 4 = 40 sq ft; total 61 sq ft. Net per room: 1,116 − 61 = 1,055 sq ft. All rooms: 1,055 × 24 = 25,320 sq ft. Two coats: 25,320 × 2 = 50,640 sq ft. Gallons: 50,640 ÷ 350 = 144.7 gal. With 10% waste: 144.7 × 1.10 = 159.2 gal.
Order 32 pails of 5 gal (160 gal). Material cost: 32 × $135 = $4,320.
Notes for the bid file: same color across 24 rooms means one batch family - box pails per room so a room is not split between lots. The 10% waste allowance covers cut-in cans, roller covers left loaded, and touch-up; on a 24-room repeat it is defensible, but only if the crew does not leave half-full pails to skin over between rooms.
2. Compute labor hours, determine the crew size that fits the 12-shift window, and state the float you are carrying.
Read the worked answer
Labor hours at the stated rate: 50,640 ÷ 350 = 144.7 hours of rolling, two coats included in the rate. Allow 20% for masking, moving furniture and wall items, set-up and teardown each night, and touch-up: 144.7 × 1.20 = about 174 labor-hours.
Available per painter: 12 shifts × 7 productive hours = 84 hours. Crew needed: 174 ÷ 84 = 2.07, so round up to 3 painters. Two painters would each need about 87 hours - over the 84 available, with no allowance for a bad night, and a single call-out would break the schedule.
With 3 painters: 174 ÷ (3 × 7) = 8.3, so 9 shifts of production inside a 12-shift window - 3 shifts of float. That float absorbs access delays, a security escort running late, and a room that needs extra prep.
Direct cost reference: labor 174 × $42 = $7,308; material $4,320; direct total about $11,628 before sundries, overhead, and profit. Sundries (rollers, tape, plastic, sanding, brushes) are typically carried at roughly 5–6% of labor - about $400 - and belong in the lump sum, not in a surprise later.
3. The lump sum is firm. List the estimate risks you must price or exclude in writing, and explain how each one changes the number.
Read the worked answer
A firm lump sum on an occupied school turns on what is in scope and what is not:
- Room clearance. If the district does not empty and clear walls, your crew moves furniture and re-hangs items every night; that labor is already inside the 20% allowance, so additional content means a change order or a higher rate.
- Coatings beyond two. Marked, patched, or previously scrubbed walls may need stain-blocking primer; carry a unit price per room rather than absorbing it.
- Recoat window in humid weather. A waterborne system that does not dry overnight pushes the second coat to the next visit and forces revisits; either schedule one room-set per night or add air movement, and price the risk.
- Night access and security. Badging, escort, alarm codes, and a locked-building walkthrough at midnight consume productive time - that is why the estimate uses 7 hours, not 8.
- Shift premium. If $42/hr is a day rate, nights cost more; confirm the rate before submitting.
- Exclusions. Ceilings, doors and frames, trim, and exterior are excluded in writing. Those items are the classic scope creep on a "walls only" bid.
- Contingency. On a 12-shift firm price, carry a stated contingency - a few percent - rather than hiding it inside the production rate, so if the district asks you to justify a change you can point to the line.
Bid the number you can defend, attach the assumptions, and put the unit prices in the proposal.