The sill or cill is installed to the bottom of the window/door to allow a projection over brickwork to carry water away and allow it to run off safely to the external of the building. Without a sill there is a risk that water can run into the cavity and cause leaks inside the property. If you have a stone/concrete sill, you usually won’t require a sill with your window/door.
It’s important to note, that our sliding sash windows are all fitted with an integral sill, the sill is the bottom section of the frame. The amount of projection can be specified by you/your installer depending on your requirements. For example, if your sash window is going onto a stone sill, it will still have it’s integral sill, however, it will have no external projection.