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How do you measure bottom clearance on a fire door?

LGreene

LGreene

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Oct 20, 2009
Messages
1,154
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San Miguel de Allende, Mexico
I could really use some AHJ advice on the question I just posted on iDigHardware. In short, a fire door must have no more than 3/4-inch clearance at the bottom. How is this measured if the clearance is different on the push side and the pull side of the door because of the flooring condition? What if the clearance is less than 3/4-inch on one side, but more than 3/4-inch on the other? There's a drawing here: https://idighardware.com/2018/08/qq-wwyd-door-bottom-clearance/.
 
Thanks Charles -

I know that the clearance has to be within the acceptable limits across the width of the opening, but I don't see anything in that article about the difference between one side of the door and the other. All of the examples show level flooring below the door.
 
Lori
"...no more than 3/4-inch clearance..." Maximum.
  • your drawing does not comply.
  • replace the threshold or put on a rated door bottom
If anything, it would be on the fire side....
 
LGreene said:
That makes sense - thanks Mark. How do you know which side is the fire side? Couldn't the fire be on either side?
Click to expand...

And also...if the drawing is not compliant, a rated door bottom would not solve the problem unless the door bottom is listed for use on a door with excessive clearances. There are only a few products that have currently been tested for that.
 
“””Clearance dimensions under swinging fire doors are subject to the levelness and flatness of the floor surface directly beneath the doors. Low spots in floor surfaces can create non-compliant conditions that re- quire mitigation. “””
 
I think this has to do with a door that has variable clearances from one edge to the other (across the 3' or 6' width). We see that all the time and it can create a big problem.
 
mark handler said:
"...no more than 3/4-inch clearance..." Maximum
Click to expand...

Reading in NFPA 80 (2012, the latest one I have at the moment), para. 4.8.2 is about sills if there is a combustible floor or floor covering and it pretty clearly wants the sill to cover a minimum distance, including the full thickness of the door. That, plus the word "maximum" suggest to me that the sketch would non-compliant.
 
LGreene said:
That makes sense - thanks Mark. How do you know which side is the fire side? Couldn't the fire be on either side?
Click to expand...
Ii could, but many times you are protecting one side from the other.
A corridor would be protected from a laboratory
laboratory-fire side
 
mark handler said:
Ii could, but many times you are protecting one side from the other.
A corridor would be protected from a laboratory
laboratory-fire side
Click to expand...


Indirectly makes sense

I would say you are protecting the opening in a rated wall, so yes in some instances you would anticipate the fire to start on one side.
 
mtlogcabin said:
A fire rated metal door will only meet the 3/4" requirement on each face of the door. I believe you have met the intent of the 3/4" max clearance if it is on only one side of the door as shown in the posted link. You can always install a fire rated door sweep to the bottom of the other side depending on the door swing

https://hdsupplysolutions.com/shop/p/36-fire-rated-door-sweep-aluminum-p808415
Click to expand...

Thanks! I think many AHJs would accept the sweep on the side with the larger clearance, but technically that sweep is listed for use on doors that are compliant with NFPA 80. So it's a compromise that might make the condition more acceptable to the AHJ but it doesn't actually address the problem if there is one. While the sweep could potentially reduce the amount of smoke infiltration at the bottom of the door, that's not where the smoke travels. During the test for air/smoke infiltration, the bottom 6" of the opening is covered so that area is not taken into consideration. The head, jambs, and meeting stiles are where the airflow is measured and limited.

I really appreciate your help!
 
mark handler said:
Ii could, but many times you are protecting one side from the other.
A corridor would be protected from a laboratory
laboratory-fire side
Click to expand...

During the fire test, there is definitely one side of the door that faces the furnace, but once installed the assembly should withstand fire from either side. For example, in an apartment fire, the door to the apartment of fire origin should prevent the fire from spreading to the corridor and other units. But in the building shown in these photos: https://idighardware.com/2017/04/another-fire-door-win-2/, the fire traveled to the corridor and the fire doors contained it to the corridor and did not allow the fire to spread to the units with closed doors.
 
Max is max.....With A HM door, I would say that it is tested and listed with the "step up" in the middle so I wouldn't have an issue with that....But crooked floor or door cut I would call out...
 
Sleepy said:
Reading in NFPA 80 (2012, the latest one I have at the moment), para. 4.8.2 is about sills if there is a combustible floor or floor covering and it pretty clearly wants the sill to cover a minimum distance, including the full thickness of the door. That, plus the word "maximum" suggest to me that the sketch would non-compliant.
Click to expand...

There's a lot of confusion about sills because people think sill = threshold so the 2016 edition of NFPA 80 clarified this a bit. The sill is defined as a structural component of the building and a threshold is defined as a builders hardware component. Previous editions used the term sill somewhat interchangeably. Here's what the NFPA 80-2016 Handbook says:

A component located in the bottom part of an opening is often incorrectly referred to as a sill. The component forming the bottom part of an opening where the fire door closes is only a true sill if it is a structural component, not simply aesthetic or serving another function such as connecting multiple types of floor coverings. See also the new definition of threshold in 3.3.127, which was added to the 2016 edition to clarify the application of sill versus threshold.

In the drawing I posted, the sill would be the line at the very bottom. You gave me an idea for today's blog post. :)
 
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