The bottom plate is the lower horizontal framing member of a stud wall. In single and multi-family housing when a stud wall is placed on top of a subfloor or other wood substrate, a bottom plate is typically some version of a stress-graded dimensional lumber, either 2x4 or 2x6 in most cases, but occasionally greater if necessary. In instances when the bottom plate will be placed on concrete, either a slab or foundation wall, a pressure-treated bottom plate of similarly sized stress-graded dimensional lumber will be used.
The bottom plate will match the stud size in width and can be spliced at one or more studs to form a longer wall than would be possible with stock inventory. In wall panel applications, multiple panels can be set in succession to create a longer wall that is joined at the double plate (also known as the very top plate) to create as long a wall as desired. It is common to see automated layout markings for studs, king studs, jack studs, and cripples applied when the bottom plate is cut to length by an automated computer driven saw derived from the wall panel CAD software. This adds efficiency and accuracy to the wall panel manufacturing process.
Nails perpendicular to the bottom plate attach studs at 16” or 24” on-center spacing. The bottom plate also serves an important role in providing wood fiber for perimeter nailing of structural and/or insulated sheathing. In some areas where additional shear panel nailing is required, the bottom plate will be “up-sized” to 4x material or greater, depending on the shear panel nailing schedule. The bottom plate is typically removed in the field from the wall at door openings to allow for the door threshold to sit directly on the floor surface.