Above grade refers to a subfloor's elevation in comparison to the ground level (or, grade) outside the building. An above-grade subfloor is higher than the ground by 18 inches or more. Second and third stories are above the ground or grade. Above-grade subfloors are less likely to have moisture issues but are more likely to have unwanted movement or flexibility. Certain flooring products can only be installed on grade or above grade.
See grade level for all three terms designating elevation relative to grade.