Design to Maintain Minimum 8” Clearances to Protect Wood from Ground Moisture

One of the oldest and most reliable practices to prevent wood and other moisture sensitive materials from decay is to separate the wood from the constant uptake of moisture from the ground. Decay conditions can occur when wood is in direct ground contact or when moisture wicks through other materials such as concrete or masonry. Some well-known details for separation of wood from ground moisture are shown in Figure 8–1.

Most building codes require a minimum of 6” clearance between untreated wood and the exterior grade. A minimum of 8” clearance between untreated wood and the exterior ground level is recommended in this course. In other conditions shown in Figure 8–1, ground clearance recommendations vary (e.g., floor beams in crawl spaces are required to have a minimum 12” clearance to interior grade as much for reason of access as for moisture protection).