# Corridor utilized for makeup air?



## Yikes (Feb 10, 2011)

1018.5 says that corridors shall not serve as return ducts.  But what about your typical apartment building, where bathroom exhaust fans are drawing air from the living room, which in turn is pulling it from the undercut at the entry door.  How does that square with this code section?


----------



## Yankee (Feb 10, 2011)

that's not returning the air to . . . anything


----------



## RLGA (Feb 10, 2011)

What you describe seems to be addressed in Exception 1 of 1018.5.


----------



## Yikes (Feb 11, 2011)

1018.5 Air movement in corridors. Corridors shall not serve as supply, return, exhaust, relief or ventilation air ducts.

Exceptions:

1.  Use of a corridor as a source of makeup air for exhaust systems in small rooms of 30 square feet or less *[nope, most bathrooms are larger than this]* that open directly onto such corridors *[nope, most bathrooms open into the bedroom or living room of the apartment]*, including toilet rooms, bathrooms, dressing rooms and janitor closets, shall be permitted, provided that each such corridor is directly supplied with outdoor air at a rate greater than the rate of makeup air taken from the corridor.

2. Where located within a dwelling unit, the use of corridors for conveying return air shall not be prohibited.  *[when was the last time you saw a corridor **within** a dwelling unit?  At the White House?]*

In the "bad old days" of poorly sealed windows, we could count on enough leakage to not worry about makeup air.  but with tighter building construction, I believe the typical bathroom or kitchen exhast fan really is pulling air from the main corridor via the undercut at every apartment's 20 minute smoke-sealed entry door in multifamily buildings (single-or double loaded corridors).


----------



## texasbo (Feb 11, 2011)

Yikes, do you typically see dwelling units at a lower pressure than the corridor?


----------



## Yikes (Feb 11, 2011)

Well, if the bath fan and the range hood are running, then I would expect they would be negative pressure differential at the entry door at corridor.

Until recently, most of my apartments have relied on their own exterior windows for fresh air.

For the corridor, my mechanical engineers have provided a fresh air supply.

When the apartment windows are closed and a bath and/or kitchen exhaust fan are operating, the makeup air for the apartment must logically be coming from the corridor and its fresh air supply.

The developers also like this because if somebody is cooking smelly food in their apartment, the smell won't get pulled into the corridor.


----------



## brudgers (Feb 11, 2011)

Yikes said:
			
		

> 1018.5 says that corridors shall not serve as return ducts.  But what about your typical apartment building, where bathroom exhaust fans are drawing air from the living room, which in turn is pulling it from the undercut at the entry door.  How does that square with this code section?


Does the undercut of the rated corridor door have a fire damper?


----------



## Dr. J (Feb 11, 2011)

> small rooms of 30 square feet or less


 Where did that come from - not in IBC.

But otherwise, I agree - the toilet room has to be directly off the corridor to apply this exception.  One more reason the use of operable windows as the only means of outside air ventilation is generally not code compliant.

Each apartment must have a direct supply of outside air.  How else does one meet this requirement, as well as the simultaneous requirements of IMC 401.3 "_Ventilation shall be provided during the periods that the room or space is occupied._", and IBC 1204.1 "_Interior spaces intended for human occupancy shall be provided with active or passive space-heating systems capable of maintaining a minimum indoor temperature of 68°F (20°C) at a point 3 feet (914 mm) above the floor on the design heating day._"?

If I were an AHJ, I would make everyone who submits a project with natural ventilation show how 1) exhaust make-up is accomplished (window operators interlocked with the fan?); 2)How ventilation IS PROVIDED (not just "provisions for") whenever the place is occupied (window operators on occupancy sensors?); and 3) how the room is kept at 68°F with the window open on a design day (heated air curtain?).


----------



## Dr. J (Feb 11, 2011)

One more code section that must be complied with that generally cant be met with windows only:  IMC 501.3"_... If only a mechanical exhaust system is installed for a room or if a greater quantity of air is removed by a mechanical exhaust system than is supplied by a mechanical ventilating supply system for a room, adequate make-up air consisting of supply air, transfer air or outdoor air shall be provided to satisfy the deficiency. The __calculated building infiltration rate shall not be utilized to satisfy the requirements of this section__._"


----------



## Yikes (Feb 11, 2011)

Dr. J - the "30 square feet or less" is in the 2010 California modifications to the IBC.  I agree that we can no longer utilize building infiltration, both from a code standpoint and from real-world conditions.

brudgers - the requirements for smoke seals at corridors doors are for the top and sides of the door opening, not the threshold.

That leaves the question of its fire resistance:

The maximum undercut of a fire rated door per is 3/8" at the bottom edge IBC / CBC Referenced standard 12-7-404(b)9 for "fire door assembly tests", which states:

_9. Clearances for swinging doors shall be (with a minus 1/16-inch tolerance) as follows: 1/8 inch along the meeting edge of doors in pairs, 3/8 inch at the bottom edge of single swing doors and 1/4 inch at the bottom edge of a pair of doors. _

On a typical 36" wide door, a 3/8" clearance x 36" width = 13.5 max. square inches, roughly equivalent to a 4" diameter bath exhaust vent.


----------



## texasbo (Feb 11, 2011)

Brudgers question is valid, but Yikes is right; the installation of a rated door with seals satisfies the requirement for opening protection. Even if a damper is installed at openings, that doesn't keep the corridor from conveying air, except when the damper closes. And the code doesn't limit the conveyance of air only when there is a fire.

DrJ makes a point that I've seen him make in other threads, and while it might be legitimate, it is virtually unenforceable; the code allows natural ventilation, and interlocking the windows with the fan is simply not practical. Who among us can get away with that? Furthermore, the 2006 IMC 403.1 says that ventilation systems shall not be prohibited from producing positive or negative pressure, so even if we were assured of adequate ventilation, by code the room or space could be negative in relation to the corridor.

So really, what we are left with, in my opinion, is that if you have undercut doors, the rooms/spaces served by the corridor would have to be positively pressurized in relation to the corridor to maintain compliance with 1018.5, 2006 IBC, or get rid of the undercut.


----------



## Yikes (Feb 11, 2011)

texasbo - wouldn't it be more accurate to say the rooms/spaces served by7 the corridor wold have to be _neutrally pressurized_ in relation to the corridor?

If it was positively pressurized, then there would still be conveyance of air between the two spaces.

Yet a netural pressurization is practically impossible in the apartment building situation I've described above, unless each apartment unit has its own individual supply air duct directly from the exterior.

I must be missing something here...


----------



## texasbo (Feb 11, 2011)

Good point Yikes. I think the truth is, that in hotels and apartments, if you have undercut doors, it doesn't comply. I allowed it once, in a very large resort hotel, only because the mechanical engineer certified it as part of the smoke management system.  I haven't bothered looking to see if that's still an option in the 2009. My guess is that this is an often violated provision of the codes.


----------



## brudgers (Feb 12, 2011)

Yikes said:
			
		

> Dr. J - the "30 square feet or less" is in the 2010 California modifications to the IBC.  I agree that we can no longer utilize building infiltration, both from a code standpoint and from real-world conditions.brudgers - the requirements for smoke seals at corridors doors are for the top and sides of the door opening, not the threshold.
> 
> That leaves the question of its fire resistance:
> 
> ...


I'm not a mechanical engineer, but I don't think you can get 75 cfm through a 3/8" undercut using only a standard fan.


----------



## texasbo (Feb 12, 2011)

You're probably right, since the undercut only provides about half the area usually required for a duct to move 75 CFM.

And the more I think about this, the more I wonder if this is really a situation the code is intended to address.

I think the real intent is to prevent the design of corridors to be used as ducts, and not a temporary pressure imbalance, which is unavoidable.


----------



## Dr. J (Feb 15, 2011)

> I think the real intent is to prevent the design of corridors to be used as ducts


 Exactly.  If the designer has to explain how the air is getting into the exhaust fan by saying "It comes in through the corridor, to the apartment, and up the exhaust fan" it is in violation of IBC 1018.5; If he says "it is coming in through the cracks in closed windows and walls", it is in violation of IMC 501.3; and if he says it is coming in through open windows it is probably in violation of IBC 1204.1 (unless they  have a very unique heating system).


----------



## Yikes (Feb 15, 2011)

@DR. J - I agree with everything you just said.  So does that mean each apartment really needs its own fresh air supply from the exterior of the building, just for makeup air for the bath fan, kitchen fan, and clothes dryer?  ...and in cold climates or with high energy performance standards, a heat exchanger with the exhaust air, to condition each apartment?  When was the last time any of you saw this on a set of plans?

...or should we simply turn a blind eye, the mechanical engineering equivalent of "don't ask, don't tell"?


----------

