# Interior door undercut



## skipharper (Jul 27, 2016)

Has anyone ever seen any requirement as to the maximum you can undercut a hinged interior door?


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## Builder Bob (Jul 27, 2016)

Fire rated doors yes..... unrated interior doors no - the code doesn't require anything except for a maximum leaf size for a side-swing door if it isn't rated (Hardware may have to be accessible) .

A rated door must meet the requirements of NFPA 80 .


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## Francis Vineyard (Jul 27, 2016)

No, but it would be subjective to determine what amount constitutes an invasion of privacy for bathroom doors.


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## cda (Jul 27, 2016)

Rated door


http://idighardware.com/2009/04/fire-door-clearanceundercut/


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## north star (Jul 27, 2016)

*@ = @ = @*


Francis,

How much privacy is there in an enclosed toilet stall anyways
[  *RE:* Section 1210.3.1,  `12 IBC  ] ?


*@ = @ = @*


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## ADAguy (Jul 27, 2016)

It depends, if it is a corridor door of a tenant space with separate zoned AC it may upset the air balance if it is too large.


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## Pcinspector1 (Jul 27, 2016)

It might help to cut the bottom of the door to reduce inside pressures like when the front door is opened and the hollow core bathroom door shuts.


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## conarb (Jul 27, 2016)

I've had HVAC subcontractors calculate the amount of undercut for return air since return air is almost never ducted to each room, apparently you can't undercut too much, only not enough. The becomes very important in some occupancies like hospitals where negative and positive pressures are called for in each room, hallway, etc.


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## Paul Sweet (Jul 27, 2016)

A practical limit is the height of the bottom rail.  You don't want to cut it out completely, especially in a hollow core door.  An inch or so is typical, and is adequate for about 100 CFM.


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