Paul Goldense of Goldense Building Products showed me this pair of fire-rated doors last week. He mentioned that the architect had to change the arch to make it a “flatter” curve because of the rating, and that they had to use continuous hinges instead of butt hinges. Who can tell me why?
This was a tough one. When Paul mentioned it to me I had never thought of it before. I think about this stuff a lot, so it’s rare to find something in NFPA 80 that I’ve never noticed. It has to do with the top hinge location. There are several graphics in Annex F of NFPA 80, which show the required hardware locations for rated doors. The one on the right shows the requirements for rated wood doors.
With butt hinges, the top hinge has to be no more than 9 3/4″ from the top of the door to the center of the hinge. I didn’t see a similar graphic for continuous hinges, but if you look at the diagram for butt hinges and assume a 4 1/2″ high hinge, the top of the hinge would be 7 1/2″ from the underside of the frame head (7 3/8″ from the top of the door). If the arch was higher, the top of the top hinge would not be within the required distance from the top of the door.
Although this looks like a nice pair of wood doors, it’s actually a 3-hour rated hollow metal pair. The hinge reinforcement for a standard hinge would have extended past the top of the top hinge, so in order to get the top of the hinge close enough to the top of the door to satisfy NFPA 80, continuous hinges were used. Since the reinforcement for a continuous hinge doesn’t have to run past the top of the hinge, this application left more space for the arch.
For anyone who is wondering why there is wood applied over the rated hollow metal frame, that was not done by the door and frame supplier, and is likely not allowed by the frame manufacturer’s listings.