A soffit is an architectural feature, typically referring to the horizontal underside of any construction element, whether interior or exterior. Its most common form is found beneath the eaves of a roof, where it connects the exterior wall to the projecting roof edge. Soffits may also incorporate or suggest the presence of exposed beams. The vertical finishing edge that runs along the perimeter of the roof is known as the fascia

Soffit is the underside (but not base) of any construction element