A section drawing is cut through a building at line "A-A" as shown on the floor plan. The section shows a foundation wall that extends 3 feet below grade. If the floor elevation is 100.5 feet, what is the elevation at the bottom of the foundation?
Correct Answer
B) 97.5 feet
The foundation extends 3 feet below grade. Assuming grade level equals floor elevation (100.5 feet), the bottom of foundation is 100.5 - 3.0 = 97.5 feet. Note that in practice, grade and floor elevations may differ.
Why This Is the Correct Answer
Option B is correct because the foundation extends 3 feet below grade level. When grade level is assumed to be at the same elevation as the floor (100.5 feet), we subtract the 3-foot foundation depth from the grade elevation. This calculation gives us 100.5 - 3.0 = 97.5 feet as the elevation at the bottom of the foundation. This is a standard approach when grade and floor elevations are considered equivalent in the problem.
Why the Other Options Are Wrong
Option A: 96.5 feet
Option A (96.5 feet) is incorrect because it represents a 4-foot depth below grade (100.5 - 4.0 = 96.5), which exceeds the specified 3-foot foundation depth.
Option C: 98.5 feet
Option C (98.5 feet) is incorrect because it represents only a 2-foot depth below grade (100.5 - 2.0 = 98.5), which is less than the specified 3-foot foundation depth.
Option D: 99.5 feet
Option D (99.5 feet) is incorrect because it represents only a 1-foot depth below grade (100.5 - 1.0 = 99.5), which is significantly less than the specified 3-foot foundation depth.
Memory Technique
Remember 'Down and Out' - when going DOWN into the ground, subtract the depth to find the bottom elevation OUT of your reference point.
Reference Hint
Florida Building Code, Chapter 18 (Soils and Foundations) or architectural drawing standards section for elevation calculations and foundation details
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