What is Sill ?

Definition of Sill in Construction

The bottom of a system, window, door, framing member. The sill is a common reference for the last member prior to the ground, or the supporting structure below. The reference to sill is usually meant to be in the ground. For example, a mud sill, is a piece of wood or other material, that is located beneath a structural column or support. The mud sill distributes the forces caused by the weight of the structure above on the column or support. By distributing the weight evenly , the effect of the load on the ground is minimized and reduces the settlement down into the ground. A sill plate is another example of the term, however most of the time the sill plate will sit on another supportive structure. The initial framing piece on the top of the foundation wall in a wood framed structure, is referenced as the sill plate. The application of the sill plate on the top of a foundation wall, is usually over a sill sealer, which is a foam or synthetic material, to allow the plate to sit fully on the top of the concrete wall. The foam or sill sealer, provides a compressive material, that fills in the gaps under the sill plate and the foundation wall.