# Are these utility / janitor closets considered plenums?



## Mech (May 22, 2013)

'09 IBC & IMC

Three story student housing apartment building

The common area corridor separating dwelling units is being air conditioned and provided with mechanical ventilation.  If the corridor's required ventilation air is transferred through a common wall into the utility / janitor closet and then sucked out of the closet by an exhaust fan, is the closet considered a plenum?  There is no supply or return air in the closet, just the transferred air and an exhaust.  Is this any different than transferring air into a bathroom through a door grille or an undercut door and then sucking it out with a fan?

All electrical panels will be located in areas outside these three utility rooms.  Telephone, internet, and/or cable tv distribution may or may not occur in these utility / janitor rooms.  One utility room will double as the elevator room.

Thanks.


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## north star (May 22, 2013)

*= = + = =*

From the `09 IMC, Ch. 2 - Definitions:

*"PLENUM:* An enclosed portion of the building structure,

other than an occupiable space being conditioned, that

is designed to allow air movement, and thereby serve as

part of an air distribution system."

*+ + = + +*


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## klarenbeek (May 22, 2013)

I'd be OK with it.  I would consider the transfers as makeup air for the exhaust fans that serve the utility rooms, not just relief for the corridor ventilation, just as in the bathroom scenario.


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## mtlogcabin (May 22, 2013)

> If the corridor's required ventilation air is transferred through a common wall into the utility / janitor closet and then sucked out of the closet by an exhaust fan,


 I am going to assume by your post the air is being exhausted out of the building and not part of the return air. If that is correct then it is part of air exhaust and not part of the air distribution system and therefore permitted. Since the janitors closet communicates with the corridor is a fire damper required? Just asking


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## Mech (May 23, 2013)

> Since the janitors closet communicates with the corridor is a fire damper required? Just asking


This common wall does not need to be fire rated, but thanks for asking.

Each corridor needs 76 cfm.  Each utility / janitor closet - not as much, but we may as well use the same exhaust system for all the exhaust air.

Thanks for the input.


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## steveray (May 23, 2013)

"One utility room will double as the elevator room."

3006.4 Machine rooms and machinery spaces.

Elevator machine rooms and machinery spaces shall be enclosed with construction having a fire-resistance rating not less than the required rating of the hoistway enclosure served by the machinery. Openings shall be protected with assemblies having a fire-resistance rating not less than that required for the hoistway enclosure doors.

3006.6 Plumbing systems.

Plumbing systems shall not be located in elevator equipment rooms.


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## Mech (May 23, 2013)

> "One utility room will double as the elevator room."3006.4 Machine rooms and machinery spaces.
> 
> Elevator machine rooms and machinery spaces shall be enclosed with  construction having a fire-resistance rating not less than the required  rating of the hoistway enclosure served by the machinery. Openings shall  be protected with assemblies having a fire-resistance rating not less  than that required for the hoistway enclosure doors.
> 
> ...


I guess the equipment is going in the shaft with a rated access door.

Thanks for the help.


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