What is the minimum nominal thickness for an 8 foot high hollow masonry foundation wall that is 4 feet below finish grade on the exterior?

What is the minimum nominal thickness for an 8 foot high hollow masonry foundation wall that is 4 feet below finish grade on the exterior?

• A. 6 inches
• B. 8 inches
• C. 10 inches
• D. 12 inches

Answer: (B)

Eight inches is the minimum thickness for hollow masonry foundation walls. Hollow concrete masonry unit (CMU) walls used in residential foundations are typically designed to be 8 inches thick to provide enough strength, to accommodate grout and any required reinforcement, and to resist the lateral earth pressures they encounter. A thinner wall, like six inches, would be too weak for foundation service loads and for proper grout/reinforcement details. Increasing beyond eight inches isn’t required here unless there are special loading or frost considerations, but for a standard hollow CMU foundation wall, eight inches is the standard minimum. The wall being eight feet high or four feet below finish grade doesn’t change this minimum—it’s the type of masonry and its structural capability that sets the requirement.

Eight inches is the minimum thickness for hollow masonry foundation walls. Hollow concrete masonry unit (CMU) walls used in residential foundations are typically designed to be 8 inches thick to provide enough strength, to accommodate grout and any required reinforcement, and to resist the lateral earth pressures they encounter. A thinner wall, like six inches, would be too weak for foundation service loads and for proper grout/reinforcement details. Increasing beyond eight inches isn’t required here unless there are special loading or frost considerations, but for a standard hollow CMU foundation wall, eight inches is the standard minimum. The wall being eight feet high or four feet below finish grade doesn’t change this minimum—it’s the type of masonry and its structural capability that sets the requirement.