Untreated joists should be at least _____ inches above ground.

Untreated joists should be installed at least 18 inches above the ground to prevent decay and damage from moisture and pests. This clearance allows for adequate ventilation and helps reduce the chances of wood rot, which can occur when joists are in direct contact with damp soil or standing water. Ensuring this minimum distance is an important aspect of building codes and best practices in construction, particularly in areas prone to high humidity or flooding. The other choices do not align with the recommended guidelines for protecting untreated wood components from moisture-related issues.