Under the residential code's general rule, how much must the finished grade fall within the first 10 feet from the foundation?
- At least 2 inches
- At least 12 inches
- At least 3 inches
- At least 6 inches
Show the answer
D. At least 6 inches
The grade must fall a minimum of 6 inches within the first 10 feet. Where lot lines or other barriers prevent that, drains or swales are used instead. Two inches in 10 feet is the kind of slope used for impervious surfaces and is too flat for soil against a foundation.
Reference: IRC 2021, Chapter 4 (Foundations): drainage
Finished grade drops 6 inches over the first 10 feet from a foundation. What is that slope expressed as a percentage?
Answer in percent.
Show the answer
5 percent
Convert to the same units: 6 in = 0.5 ft. Slope = rise / run = 0.5 / 10 = 0.05 = 5%.
Reference: IRC 2021, Chapter 4 (Foundations): drainage; slope arithmetic
What does the load-bearing value of a soil tell the inspector or designer?
- How deep the frost line is expected to be at the building site
- How much pressure the soil can safely support, in psf
- How quickly water will drain through the soil after a storm
- How much the soil will weigh when it is used as backfill
Show the answer
B. How much pressure the soil can safely support, in psf
Load-bearing value (bearing capacity) is the pressure the soil can safely carry under a footing, in psf. It is what determines how wide a footing must be for a given load. Frost depth and drainage rate are different soil properties.
Reference: IRC 2021, Chapter 4 (Foundations): soil tests; presumptive load-bearing values