A hidden shaft down to the basement (Background Report)

UNDER THE CONCRETE FLOOR of a storage closet that houses our sanctuary building’s electric meters, under the shed roof between the building and the play yard, is an opening to a vertical shaft.

Raised platform on floor of storage closet 
(marked by dotted red lines)

Below the jump, this post describes the shaft’s configuration, how it connects to the basement, its purpose, and its history—according to inferences drawn from my exploration of it this week.…

Configuration

As visible in the photo above, there is a raised platform in the middle of the closet. A narrow sheet of plywood is wedged along the front edge of the platform. It functions as a cover, for pulling it up reveals the opening to a nearly cube-shaped concrete shaft, 41½” x 48” and about 4’ deep. 

Suspended near the top is the remnant of a wire mesh cover over the opening that has long since fallen away. Hence a number of items have fallen into the shaft over the years and are lying at the bottom. (The view below is at an angle because I used a selfie stick to insert my phone into the shaft.)

That shaft, in turn, opens to a wide sheet-metal duct. It ultimately connects to the furnace room in the basement, which is shown below. Notice the open shaft in the room’s ceiling, and next to it another vertical shaft of the same size that opens at its bottom.

One proof of the connection to the basement room is that the light from it is visible from the entrance of the concrete shaft above. In the next image, the view is from just inside the top opening, looking down and to the right (with the aid of the selfie stick).

Purpose

The shaft-and-duct system must have been used to supply make-up air for the burners of the basement’s gas furnace (which is no longer operational).

History

This shaft was not part of the original structure as completed in either 1941 (basement) or 1948 (main floor). That conclusion is based on the following observations.

• The shaft covers over a portion of the original light-green stucco of the sanctuary building’s exterior wall, and the opening to the metal ductwork is unfinished. Apparently the shaft was constructed sometime after the sanctuary building was already completed.
• The ductwork must be secondary, for it encloses a much bigger space than was required simply to provide air to the vents in the furnace room. (To get the view below, I put my phone up through the open vent in the ceiling and pointed it to the south. The adjacent shaft is in the foreground.)

Even so, the concrete shaft has evidently been in place for a long time, judging from the amount of debris at its bottom. Some of that stuff seems larger than the present opening at its top, so how did it manage to fall in? Apparently both the shaft and the collapse of the screen over its opening predate the construction of the 6"-high plywood platform atop the adjacent landing at the top of the steps, which had the effect of narrowing the shaft’s opening.