How old is the building I work in?

I work within the hallowed walls of an institution of higher education. However, for the last week or so, I have noticed a large cobweb on one of the framed pieces of art that decorates a stairwell I use regularly. Now, don't ge me wrong, I realize that cleaning is a little bit over-rated, but, you've got to wonder how long this web has been on this picture. My spidey sense is telling me that there is a big spider where this web came from and I hope that the two of us don't have to tango anytime soon.