soffit

noun

1. The visible underside of an arch, balcony, beam, cornice, staircase, vault or any other architectural element.

   “From 1945 onwards, deterioration in the condition of the brickwork in the arch soffits was kept under close observation, and in 1951 it was decided that strengthening must be undertaken.”

   “If the soffit is to be sloping, simply attach the soffit board(s) to the underside of the rafters, butting the edges tight against the fascia board in front and the barn siding in the back.”

   “A soffit is the underside of any part of a building's structure. Most people know about the soffit boards below their fascia boards (which cap off the ends of a roof's rafters). But if you walk through a brick-built tunnel and glance upwards, for example, you will be looking at the soffit of the arch.”

2. The top point of the inside open section of a pipe or box conduit.

   “The elevation of the pipe soffit is 10.4 meters above mean sea level.”

   “The vents on the bottom of the soffit should be open, and the vents on the side of the soffit should be closed.”