A sill in construction is the bottom horizontal member of a wall or building frame to which vertical members, like studs, are attached. It's also commonly referred to as a sill plate or sole plate. The term "plate" is often omitted in everyday carpentry, and it may also be known as a ground plate, ground sill, groundsel, or midnight sill.
Function of a Sill
The sill serves several crucial purposes:
- Provides a solid base for the wall: It distributes the weight of the wall evenly onto the foundation.
- Anchors the wall to the foundation: Sills are typically bolted to the foundation, providing stability and preventing the wall from shifting.
- Creates a level surface for construction: The sill ensures the wall is built on a flat and even plane.
- Provides a fastening point for wall studs: Studs are nailed or screwed to the sill, creating the wall frame.
- Helps to prevent moisture intrusion: When properly installed with a moisture barrier, the sill helps protect the wall from ground moisture.
Sill Material
Sills are typically made of treated lumber to resist rot and insect infestation, especially when in contact with concrete or near the ground. Pressure-treated lumber is commonly used.
Examples of Sill Usage
- Foundation Sill: The sill that rests directly on the foundation wall.
- Window Sill: The horizontal piece at the bottom of a window opening.
- Door Sill: The horizontal piece at the bottom of a door opening.
In summary, the sill is a critical structural component that forms the base of a wall, providing support, anchoring, and a level surface for construction, while also offering protection against moisture.
