The builders called the RSPCA to help rescue the animal which had become stuck in an office they were renovating at the de Havilland campus in Hatfield.
RSPCA animal welfare officer Kate Wright eventually freed the fox after the construction team levered-up the floor with crowbars.
She said: “The builders were amazing and when I said the best thing for the rescue was to remove the floor panel he was stuck in, they sorted it out immediately using crowbars.
“Then it was a case of me crawling on the floor and trying to then squeeze the fox’s head back through the hole.
“He couldn’t move any other part of his body, so he just sat there watching me the whole time.
“I actually think he had quite an embarrassed expression on his face.
“I had to get to the scruff of his neck while trying to avoid wires and eventually after a lot of pushing, I managed to pop one ear through and then finally the next and he was free.”