Stretching the Limit?

[DwightB]

Using IBC 2006:

I have a plan for a 100' x 200' assembly building with an additional 41' of ancillary spaces (class, office, kitchen, restrooms) along the long side and on two levels. Total main level area inside the walls: 27,804 SF.

Sprinkler system is required due to capacity (>300), and area (>12,000 SF).

90% of the perimeter has over 30' clear access; the remaining 10% is at least 29'6", so I compute at least 98% for F when calculating F/P, and F/P-.25 = 73%. The perimeter increase is 73% x 6,000 = 4,380 SF.

The client wants to use wood framing, with as little fire rating as possible. Type 5B allows 6,000 SF, the sprinkler increase adds 18,000 SF (506.3) if a one story building. So the total is 6,000 + 18,000 + 4,380 = 28,380 SF and the building qualifies, if one story.

The upper level totals 8,154 inside the walls, thus is less than 1/3 of the area below (29%) and qualifies as a mezzanine. A mezzanine does not have to be open to the "room" that it is part of (505.4, Ex. 5 [not Group H or I, not more than 2 story, and is sprinklered]) and does not need to be open space ("or portions of" is used in several exceptions).

My confusion is with a portion of 505.2 that says "the enclosed portion of a room shall not be included in a determination of the floor area of the room in which the mezzanine is located". If there are no fire separations, are the ancillary spaces on the main level "enclosed"? If they are enclosed, and not part of the main level, then am I incorrect to include in the 27,804 SF when calculating the 1/3 maximum area?

My main level open and clear space in the big room is only 19,502 SF. If that is the factor to use, then the upper level way too large for a mezzanine and I have to call it a second floor, I only get a 200% increase for the sprinkler system, and construction type has to bump up to IIIB to qualify.

Is the upper level a mezzanine here?

 

[smeismer]

Makes no difference. If it is a mezzanine, the area counts as first floor area, and you are oversize. If 2 story, then just 200% sprinkler increase, and you are oversize.

 

[mtlogcabin]

505.1 General.

A mezzanine or mezzanines in compliance with Section 505 shall be considered a portion of the story in which it is contained. Such mezzanines shall not contribute to either the building area or number of stories as regulated by Section 503.1. The area of the mezzanine shall be included in determining the fire area defined in Section 902. The clear height above and below the mezzanine floor construction shall not be less than 7 feet (2134 mm

 

[DwightB]

Smiesmer: I have to disagree on that point. Section 505.1 says "Such mezzanines shall not contribute to either the building area or number of stories.. as regulated by Sec 503.1"

 

[smeismer]

I stand corrected. Thank you.

 

[DwightB]

However, my 27,804 SF inside the exterior walls includes classes, offices, kitchen and restrooms with non-rated walls (per construction type IIIB, and Table 1017.1) that are under the "mezzanine". The code says a mezzanine does not have to be open to the area that it is associated with. In this plan, the portion of the main level below the mezzanine is also not open to that area, but is not fire-separated from it.

Am I still legal with type VB construction?

 

[AegisFPE]

I think the language in Exception 5, "...shall not be required to be open to the room in which the mezzanine is located," is intentionally identical to text in 505.2.

And, it seems reasonable that if the mezzanine need not be open to the room below, then the room below need not be open to the mezzanine, such that the contiguous area of multiple rooms below should be able to contribute to the allowable mezzanine area.

Seattle has an interesting take on 505.1 which could impact your project if your AHJ sees it similarly, that only area below the mezzanine with a minimum height of 7 feet and area outside the mezzanine with a minimum height of 14 feet (where a mezzanine could theoretically be located, but is not) can contribute to the floor area of the space below when calculating the allowable mezzanine area.

A potential alternative approach could be to add automatic fire alarm detection and notification throughout, so that occupants of the mezzanine would be readily aware of a fire developing in any room below.