Last week I got a call about a problem that led me to do some research on the difference between the clearance and the undercut on a fire door. On the project in question, the fire doors were supplied with a 5/8-inch undercut, which would typically result in a clearance dimension under the door that meets the requirements of NFPA 80. But when the frames were installed, the slab was not consistent so the bottom of the frame was not set level with the slab – the frames were set higher. When the flooring was installed and the doors were hung, the clearance between the bottom of the door and the top of the flooring was larger than the 3/4-inch maximum allowed by NFPA 80.
The contractor considers the door and frame supplier responsible for the problem – even though the supplier did not install the frames. The project is a health care facility, and the owner is requiring the newly-installed fire doors to be code-compliant, and rightly so. The supplier maintains that they provided doors with a code-compliant undercut, and can not be held responsible for the non-code-compliant clearance, since the floors are out of level and the installer did not place the bottom of the frames at floor level. So whose problem is it?
I went looking for some documentation to help clarify the difference between clearance and undercut.
The SDI Fact File includes these definitions:
UNDERCUT: The distance between the bottom of door and the bottom of the frame.
FLOOR CLEARANCE: The distance between the bottom of the door and the top of the material directly below the door. This varies with applications, such as concrete, any floor covering and/or a threshold.
The same SDI PDF includes information about setting the frame with the bottom of the frame at floor level. It’s in SDI 122 – page 23, which is page 90 of the PDF.
NAAMM/HMMA has a document called Defining Undercuts, which includes similar information and this figure indicating the undercut and the clearance:
Although NFPA 80 doesn’t clearly state the difference between the undercut and the clearance, the NFPA 80 Handbook includes a paragraph stating:
“Undercutting is not to be used interchangeably with door clearance. Many users of the document often confuse the two terms and concepts, assuming that undercut and clearance under a fire door are the same item. Chapter 4 mandates that the maximum clearance under a fire door be not more than ¾ in. (19 mm). Undercutting is the process required to achieve this ¾ in. (19 mm) door clearance. Undercutting is permitted in some job site preparation for wood and composite doors per 126.96.36.199.”
It seems clear to me that if fire doors are supplied with the proper undercut and the frames are not installed by the door and frame supplier, the supplier should not be held responsible for clearances that are not code-compliant if the frames are not set at floor level or because the floor level varies excessively from one side of the opening to the other. (Note: This is my opinion.)