In an exemplary embodiment, a window sill comprises a structural base having a first side and a second side, a fenestration cap attached to the structural base, a window frame mounted on the fenestration cap and finish elements applied to the structural base and adjacent to the fenestration cap. The window frame may be removed from the fenestration cap without disturbing the finish elements. Alternatively, a method of installing a window in a window opening comprises providing a window opening and preparing the window opening for receiving a fenestration cap, installing a fenestration cap by placement within and attachment to the window opening in a primary step, and installing a window within the window opening by placement within and attachment to the fenestration cap in a secondary step.