Question

In a wood window assembly, the sill, stool, and apron are all at the bottom. What is the difference between these components?

Answer

The sill is the exterior member upon which the window sits, sloped to drain. The stool is the horizontal interior member. Built upon and raised above the sill, it often extends beyond the window on each side to support the interior casing. The apron is the trim piece below the stool that closes the gap in the finish.