A roof area measures 2,400 square feet. If installing architectural shingles with 10% waste factor, how many squares of shingles are needed?
Correct Answer
B) 27 squares
2,400 sq ft = 24 squares (100 sq ft per square). With 10% waste: 24 × 1.10 = 26.4 squares. Round up to 27 squares since you cannot purchase partial squares.
Why This Is the Correct Answer
The calculation correctly converts 2,400 square feet to 24 squares (dividing by 100 sq ft per square), then applies the 10% waste factor (24 × 1.10 = 26.4 squares). Since shingles are sold in whole squares only, you must round up to the next whole number, which is 27 squares. This ensures adequate material coverage including the waste allowance.
Why the Other Options Are Wrong
Option A: 24 squares
This answer appears to round down from 26.4 squares, but in construction material ordering, you must always round up to ensure sufficient materials since partial squares cannot be purchased.
Option C: 26.4 squares
While this is the mathematically precise answer (26.4 squares), it's impractical because shingles are sold only in whole squares, making it impossible to purchase 0.4 of a square.
Memory Technique
Remember 'SQUARE-WASTE-UP': convert to Squares (÷100), add Waste factor, then round UP to whole numbers since you can't buy partial material bundles.
Reference Hint
Look up roofing material calculations and waste factors in the construction estimating section or roofing chapter of your contractor reference manual.
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