A saddle sill is a type of threshold designed to provide a smooth transition between two spaces, while also helping to prevent drafts, water, and other environmental elements from entering the space. It helps make things more accessible for people with mobility issues, as well as to meet the requirements of some building codes.
The use of a saddle sill can help improve energy efficiency and reduce heating and cooling costs. It is typically used when the flooring on either side of the door unit are different heights. This can occur when the door unit is being installed in a new construction or remodel project, or when the flooring on one side of the door unit has settled over time.