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Rooftop Amenity / assembly space and Construction Type

E

ETThompson

SAWHORSE
Joined
May 19, 2017
Messages
190
Location
Columbus, Ohio
Hi

I'm working on a 7-story residential apartment building. The owner has just decided to increase the size of the level 07 indoor / outdoor amenity space and I am wondering if there's any way of getting out of the increase in Construction Type required. Previously this space had been under 10% of the gross floor area but with the changes it is over.

The gross floor area of this level is 9,268 (which does not include the uncovered roof deck or tenant private roof decks - floor plate is 12,090). The outdoor area is 1,106 (partly covered) and the indoor area is 1,080 including restrooms and other support spaces. So, it appears we are not close.

The podium is 20'-0" to the top, and Level 07 is at 67'. These are measured to our level 01 finish floor, so we probably have to add about a foot to grade plane, which slopes down from level 01.

We're planning a podium approach based on 510.2. The podium is a concrete structure with PT slab at top. The building above the podium is CFMF bearing walls and metal stud construction throughout. Concrete composite slab on open web steel joists.

We are fully sprinkelered.

So we now have an A-3, non-accessory space at the highest occupied floor of the building. Per 504.2, we have to comply with the height and story limits for each occupancy.

We comply for R-2 (limited to 5 stories above podium, and would comply with Types IIA or B (85' and 75' respectively). The A-3 building complies in height (75' & 85' for Type II), but not in stories (4 max for IIA).

If we have to go to IB, we're adding significant expense and complexity.

Is there any exception or other approach that could get me out of this?

Thank you
 
There is no 2017 IBC, so I’m assuming it’s the 2015 IBC. What is the floor area for each assembly space (not aggregate floor area)? If each assembly space is under 750 sq. ft., then they can be classified with the Group R-2. If they are truely Group A-3 spaces, then there’s no choice but to go to Type IB construction. This will allow the entire building to be Type IB construction with no need to provide a Type IA podium.
 
OP indicated that the spaces each exceed 750 s.f.

The bigger question is alterations to an existing building or new construction? (Not really sure based on the OP)
 
Thanks, that was what I was afraid of.

The areas I listed for the amenity areas are individual, not aggregate (1,105 for outdoor area and 1,080 for indoor). So the aggregate total is 2,185. These are net floor areas (ie, not including surrounding walls) but I did not exclude furniture. My understanding is I could exclude that (though not sure what exactly counts - eg, movable furniture, etc), but since we are not close, I didn't bother.

Also hurting us is the fact that part of the overall gross area denominator is uncovered, so does not count towards the gross area. No way out of that that I can see.

But even if we did, I'd still have to get under 1,200 for the amenity area (10% of our full floor area including unroofed areas). Doesn't seem possible.

Thanks for all your help.
 
ETThompson1 said:
Thanks, that was what I was afraid of.

The areas I listed for the amenity areas are individual, not aggregate (1,105 for outdoor area and 1,080 for indoor). So the aggregate total is 2,185. These are net floor areas (ie, not including surrounding walls) but I did not exclude furniture. My understanding is I could exclude that (though not sure what exactly counts - eg, movable furniture, etc), but since we are not close, I didn't bother.

Also hurting us is the fact that part of the overall gross area denominator is uncovered, so does not count towards the gross area. No way out of that that I can see.

But even if we did, I'd still have to get under 1,200 for the amenity area (10% of our full floor area including unroofed areas). Doesn't seem possible.

Thanks for all your help.
Click to expand...
For determining occupant load, you can exclude permanent fixtures and building elements from the floor area (i.e., net floor area), but for allowable area, that is based on the actual floor area occupied by the occupancy group within the exterior walls.

If you have the ability to break up the Group A-3 spaces into spaces that are 750 sq. ft., then you can classify them with the main Group R-2 occupancy. Or, you can have one assembly space that is 1,200 sq. ft. that is within the Accessory Occupancy limitation and classified as Group A-3, and the other assembly spaces are at 750 sq. ft. or less to be considered as Group R-2 spaces.

The only other options are: reduce all assembly space floor areas so the aggregate is less than the 1,200 sq. ft., or reclassify the building as Type IB construction.
 
Thanks for the info, but isn't the 10% limit an aggregate for all the assembly uses on that floor? Or does that requirement go away since they are under the 750sf and become B occupancies?
 
Also, our floor plate at level 07 is 12,000 sf but because a good portion of it is uncovered, the gross area under a roof is only about 9,200sf. Just to confirm, I have to use the latter, uncovered area number, correct?
 
One last question for the night - there seems to be an imbalance between the height and stories. We pass the height easily for II (85 or 75 feet) but the stories are only 4 and 3. Doesn't this seem out of whack?
 
OK one more. Item 4 under 510.2 tells me we can have multiple A occupancies with occupant load less than 300. I guess that is telling me we can have them, but doesn't get me out of the height and story limits, correct?
 
ETThompson1 said:
Thanks for the info, but isn't the 10% limit an aggregate for all the assembly uses on that floor? Or does that requirement go away since they are under the 750sf and become B occupancies?
Click to expand...
Assembly uses for determining occupant load and assembly occupancies are two separate things. An assembly use that has an area under 750 sq. ft. is not classified as an assembly occupancy. The accessory occupancies requirements only apply to occupancy groups and not uses or functions of a space.
 
ETThompson1 said:
Also, our floor plate at level 07 is 12,000 sf but because a good portion of it is uncovered, the gross area under a roof is only about 9,200sf. Just to confirm, I have to use the latter, uncovered area number, correct?
Click to expand...
Correct. Building area is the area under the projection of the roof or floor above.
 
ETThompson1 said:
One last question for the night - there seems to be an imbalance between the height and stories. We pass the height easily for II (85 or 75 feet) but the stories are only 4 and 3. Doesn't this seem out of whack?
Click to expand...
Sort of, but some occupancy groups are permitted 5 and 6 stories.

The construction type is a broad classification of a building based on the materials used for the structural support regardless of what the building is used for. The occupancy group narrows that down by number of stories based on the relative hazard of that occupancy.
 
ETThompson1 said:
OK one more. Item 4 under 510.2 tells me we can have multiple A occupancies with occupant load less than 300. I guess that is telling me we can have them, but doesn't get me out of the height and story limits, correct?
Click to expand...
Correct. You still need to comply with the height requirements for each occupancy group.
 
Just to confirm one thing I said above, because I'm getting pressure from the owner - the outdoor, uncovered roof deck must be included in the area contributing to the consideration of accessory use, correct? Even though it is uncovered? For calculating the 10%, I have to include the uncovered roof deck area even though that area is *not* included in the denominator of the gross area of the floor? There is something strange about that.
 
ETThompson1 said:
Just to confirm one thing I said above, because I'm getting pressure from the owner - the outdoor, uncovered roof deck must be included in the area contributing to the consideration of accessory use, correct? Even though it is uncovered? For calculating the 10%, I have to include the uncovered roof deck area even though that area is *not* included in the denominator of the gross area of the floor? There is something strange about that.
Click to expand...
Good question. If the outdoor area is uncovered it is considered an occuied roof area. Unfortunately, the 2017 CBC (aka 2015 IBC) doesn't address occupied roofs in Chapter 5 like the 2018 IBC does. Section 503.1.4 of the 2018 IBC allows an occupancy on the roof if the occupancy is permitted for the story below and is not counted toward building area. Maybe you can get a code modification to utilize that section of the 2018 IBC, considering that California always seems to adopt the current IBC eventually.

Otherwise, you'll probably be required to treat the oudoor occupied area as a Group A-3 and as part of the portion of the accessory occupancy, since a Group A-3 cannot be located above the 4th story.
 
What about this concept? From this article: http://www.woodworks.org/experttip/...wable-building-size-height-area-calculations/

Requires an interpretation based on future changes to the code.
--------------------------------------------------------------
Roof Decks without Roof Coverings

IBC 2012 Table 503 and IBC 2015 Table 504.4 provide limitations on allowable number of stories in a given building. However, per the definition of a story in IBC Chapter 2, occupied roof space without structure above doesn’t technically qualify as a story per its definition:

STORY. That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above (also see “Basement,” “Building height,” “Grade plane” and “Mezzanine”). It is measured as the vertical distance from top to top of two successive tiers of beams or finished floor surfaces and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

Additionally, for most common roof deck spaces, none of the roof area would classify as a habitable space as defined in IBC Chapter 2:

HABITABLE SPACE. A space in a building for living, sleeping, eating or cooking. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable spaces.

IBC 2015 Section 1006.3 added language which specifically recognizes that occupied roofs exist and stipulates egress requirements associated with them:

1006.3 Egress from stories or occupied roofs. The means of egress system serving any story or occupied roof shall be provided with the number of exits or access to exits based on the aggregate occupant load served in accordance with this section. The path of egress travel to an exit shall not pass through more than one adjacent story.

Approved code changes set to take effect in the 2018 IBC support this point (see code change G24-15, public comment #2). IBC 2018 Section 302.1, which covers occupancy group definitions, includes the following to clarify how occupied roofs are classified: “Occupied roofs shall be classified in the group that the occupancy most nearly resembles, according to the fire safety and relative hazard involved and shall comply with Section 503.1.4.” Section 503.1.4 provides options for not requiring the occupied roof to be included in the building’s number of stories or area.

503.1.4 Occupied roofs A roof level or portion thereof shall be permitted to be used as an occupied roof provided the occupancy of the roof is an occupancy that is permitted by Table 504.4 for the story immediately below the roof. The area of the occupied roofs shall not be included in the building area as regulated by Section 506.

Exceptions:

  1. The occupancy located on an occupied roof shall not be limited to the occupancies allowed on the story immediately below the roof where the building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2 and occupant notification in accordance with Section 907.5 is provided in the area of the occupied roof.
  2. Assembly occupancies shall be permitted on roofs of open parking garages of Type I or Type II construction, in accordance with the exception to Section 903.2.1.6.
Elements or structures enclosing the occupied roof areas shall not extend more than 48 inches above the surface of the occupied roof.

Exception: Penthouses constructed in accordance with Section 1510.2 towers, domes, spires, and cupolas constructed in accordance with Section 1510.5

Although these changes won’t go into effect until the 2018 IBC, some designers have already used this approved language to justify occupied roofs and associated building size analyses.
 
It will be a challenge, but you might be able to defend it by using the definition of "building area." The uncovered area as I mentioned would be a "roof assembly" by IBC definition and would not be part of the building area, and is, therefore, not subject to the limitations of accessory occupancies. Section 1004.5 requires outdoor areas to be provided with a means of egress as required by the code (the 2018 IBC clarifies this further by including "occupied roofs" in the first sentence). Based on these loosely related sections, you could justify the enclosed assembly spaces as accessory occupancies and the unenclosed, uncovered areas as outdoor areas. But, they may counter stating that the outdoor area is a Group A-3 and, thus, is not permitted above the 4th story. This is where using the 2018 IBC may come in handy.
 
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