Grade Levels: Below-grade, On-grade, and Above/Suspended grade levels

Subfloors & Underlayments

  1. Above/Suspended – A suspended floor is one with a minimum of 18″ of well-ventilated air space below.
  2. On grade – An on-grade floor is in direct contact with ground or over a fill in direct contact with ground.
  3. Below grade – A below-grade floor is partially or completely below the surrounding grade level in direct contact with the ground or over a fill in direct contact with the ground.
Updated on August 16, 2022