Bottom Plate (Sole Plate)
The bottom plate, also called the sole plate, is the horizontal lumber at the base of a framed wall to which the studs are nailed. It rests on the subfloor or slab and anchors the wall to the floor system or foundation below. In locations with moisture exposure, pressure-treated lumber is required for bottom plates.
In-Depth Explanation
The bottom plate serves as the foundation of the wall frame, providing the base attachment for all studs and establishing the wall's position on the floor. On concrete slabs and anywhere the plate contacts masonry, building codes require pressure-treated lumber or naturally durable species to prevent rot from moisture wicking up through the concrete. A sill seal gasket or foam is typically placed between the bottom plate and the substrate to reduce air infiltration. The bottom plate is fastened to the subfloor with nails during initial wall assembly (walls are usually built flat on the floor and tilted up), and then permanently anchored to the foundation with anchor bolts or hold-down straps. At door openings, the bottom plate is initially installed continuously across the opening for structural stability during wall raising, then cut out after the wall is standing, plumbed, and secured. The plate material at door openings is discarded after cutting. Bottom plate to stud connections must follow code-specified nailing schedules, typically two 16d nails per stud end-nailed through the plate.
Usage Example
The code required pressure-treated bottom plates throughout the first floor because the walls were framed directly on the concrete slab.