Two story volumes and gross floor area.

[Tim Mailloux]

Hypothetically, say you have a two story building with an atrium or any similar two story volume that is atmospherically open to the 2nd floor. Even though there is no physical floor at the upper volume of the atrium (a giant hole in the floor), does the area of the atrium get added to the 2nd floors gross floor area?

Based on the definition of Floor Area, Gross and the corresponding code commentary I would say it does.


[BE] FLOOR AREA, GROSS. The floor area within the inside perimeter of the exterior walls of the building under consideration, exclusive of vent shafts and courts, without deduction for corridors, stairways, ramps, closets, the thick-ness of interior walls, columns or other features. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above. The gross floor area shall not include shafts with no openings or interior court.

Commentary

Gross floor area is that area measured within the perimeter formed by the inside surface of the exterior walls. The area of all occupiable and non occupiable spaces, including mechanical and elevator shafts, toilet rooms, closets and mechanical equipment rooms, are included in the gross floor area. This area could also include any covered porches, carports or other exterior space intended to be used as part of the building’s occupiable space. Both gross and net floor areas are used for the determination of occupant load in accordance with Table 1004.5


The fact that the only exclusions from the gross floor area are vent shafts (aka natural ventilation shaft with no roof) and interior courts (also with no roof), and that stairways, mechanical shafts and elevator shafts (large floor openings) are specifically included in the gross floor area would lead me to believe that a large atrium floor opening would also be included in the gross floor area of the upper floor. An interpretation I received years ago from an AHJ was that if the space in question has a floor or roof overhead, it gets included in the gross floor area whether it has a floor or not.

 

[steveray]

So are talking about for H&A or occupant load?....Either way I think I still have the same answer, but let's play this out....

 

[Tim Mailloux]

So are talking about for H&A or occupant load?....Either way I think I still have the same answer, but let's play this out....

for allowable building area, not occupant load.

 

[Tim Mailloux]

I was looking at the wrong definition. Based on the definition and code commentary for Area, Building it is very clear that these space get added to the building area for determining allowable area as per chapter 5

[BG] AREA, BUILDING.
The area included within surrounding exterior walls, or exterior walls and fire walls, exclusive of vent shafts and courts. Areas of the building not provided with surrounding walls shall be included in the building area if such areas are included within the horizontal projection of the roof or floor above.


Commentary
Allowable building areas (as established by the provisions of Chapter 5 and Table 506.2) are a function of the potential fire hazard and the level of fire endurance of the building’s structural elements, as established for the types of construction in Chapter 6. A building area is the “footprint” of the building; that is, the area measured within the perimeter formed by the inside sur-face of the exterior walls. This excludes spaces that are inside this perimeter and open to the outside atmosphere at the top, such as open shafts and courts (see Section 1205). Where a portion of the building has no exterior walls, the area regulated by Chapter 5 is defined by the projection of the roof or floor above [see Commentary Figure 202(5)]. The roof overhang on portions of a building where there are exterior enclosure walls does not add to the building area because the area is defined by exterior walls.

 

[steveray]

This is something that still needs some work.....As the allowable area is "per story"...... is the 2 story room really on both stories?

506.2.2 Mixed-occupancy buildings. The allowable area
of each story of a mixed-occupancy building shall be
determined in accordance with the applicable provisions
of, Section 508.3.2 for nonseparated occupancies and
Section 508.4.2 for separated occupancies.

 

[Tim Mailloux]

This is something that still needs some work.....As the allowable area is "per story"...... is the 2 story room really on both stories?

This is something that still needs some work.....As the allowable area is "per story"...... is the 2 story room really on both stories?

IMO the commentary is pretty clear......A building area is the “footprint” of the building; that is, the area measured within the perimeter formed by the inside surface of the exterior walls. This excludes spaces that are inside this perimeter and open to the outside atmosphere at the top, such as open shafts and courts........

 

[Tim Mailloux]

I am still interested to hear what others on this forum think, but yesterday I spoke with two well respected code consultants in CT and both agreed with my interpretation that the area of these open volumes are included in the building area.

 

[RLGA]

I have always included open areas, such as atriums, in the building area for each story. However, for occupant loads in atriums, I only include the main floor of the atrium and any balconies, stairs, and elevator hoistways within the atrium, but not the openings at each of the floors above within the gross floor area. In my opinion, it makes absolutely no sense to include large floor openings in the gross floor area when determining occupant loads.

 

[Tim Mailloux]

I have always included open areas, such as atriums, in the building area for each story. However, for occupant loads in atriums, I only include the main floor of the atrium and any balconies, stairs, and elevator hoistways within the atrium, but not the openings at each of the floors above within the gross floor area. In my opinion, it makes absolutely no sense to include large floor openings in the gross floor area when determining occupant loads.

I agree, this area question was only related to building area per Chapter 5, not Gross floor area used to determine occupant load per Chapter 10

 

[steveray]

I guess if it is that big of an open area(1/3), you could just call the second story an enclosed mezzanine (2/3) with 2 exits....And really reduce your H&A....

 

[Tim Mailloux]

I guess if it is that big of an open area(1/3), you could just call the second story an enclosed mezzanine (2/3) with 2 exits....And really reduce your H&A....

the 2 story volumes arent that big, but they are large enough to put the building area above what is allowed for the use group and construction type requiring a fire wall which is no small expense.

 

[Robert]

the 2 story volumes arent that big, but they are large enough to put the building area above what is allowed for the use group and construction type requiring a fire wall which is no small expense.

I have seen Planning Departments count tall spaces twice, with respect to building area....thinking a floor could be added later. But for Building and Fire floor areas I don't see this happening.

 

[steveray]

Put in a lot line and no firewall? Zoning probably wouldn't allow...

706.1.1 Party walls. Any wall located on a lot line
between adjacent buildings, which is used or adapted for
joint service between the two buildings, shall be
constructed as a fire wall in accordance with Section 706.
Party walls shall be constructed without openings and
shall create separate buildings.
Exceptions:
1. Openings in a party wall separating an anchor
building and a mall shall be in accordance with
Section 402.4.2.2.1.
2. Party walls and fire walls are not required on
lot lines dividing a building for ownership
purposes where the aggregate height and area
of the portions of the building located on both
sides of the lot line do not exceed the maximum
height and area requirements of this code.
For the building official’s review and approval,
the official shall be provided with copies of
dedicated access easements and contractual
agreements that permit the owners of portions

 

[Tim Mailloux]

Put in a lot line and no firewall? Zoning probably wouldn't allow...

706.1.1 Party walls. Any wall located on a lot line
between adjacent buildings, which is used or adapted for
joint service between the two buildings, shall be
constructed as a fire wall in accordance with Section 706.
Party walls shall be constructed without openings and
shall create separate buildings.
Exceptions:
1. Openings in a party wall separating an anchor
building and a mall shall be in accordance with
Section 402.4.2.2.1.
2. Party walls and fire walls are not required on
lot lines dividing a building for ownership
purposes where the aggregate height and area
of the portions of the building located on both
sides of the lot line do not exceed the maximum
height and area requirements of this code.
For the building official’s review and approval,
the official shall be provided with copies of
dedicated access easements and contractual
agreements that permit the owners of portions

The way I read that is it would only be allowed if there are two different owners. This is a public building on public property and even if it was on two lots they would both be owned by the same owner.

 

[Tim Mailloux]

As luck would have it, the SD estimate came in way over budget and we will need to cut some classrooms to get back on track. As long as we can get the maximum frontage increase we should just be able to sneak in under the max allowable area and not need a fire wall.....it going to be close.

 

[Tim Mailloux]

and CT OSBI got back to me and they agree with my interpretation that these spaces count towards the allowable building area (chapter 5)