Appeal 15194

OSSC 2014 Section 1015.2.1

1015.2.1 Two exits or exit access doorways. Where two exits or exit access doorways are required from any portion of the exit access, the exit doors or exit access doorways shall be placed a distance apart equal to not less than one-half of the length of the maximum overall diagonal dimension of the building or area to be served measured in a straight line between exit doors or exit access doorways. Interlocking or scissor stairs shall be counted as one exit stairway.

Allow the two interlocking stair shafts be considered separate building exits when they meet the following:
• The stairs will be separated by a 2-hour Fire Barrier to create two exit stairways each in its own vertical exit enclosure.
• All openings and through-penetrations will be fire-stopped as required for a vertical exit enclosure.
• The travel distance between the exit doors of the two stairs when measured along the 1-hour corridor exceeds one third the diagonal, as permitted by Exception 1 and 2 of 1015.2.1.

See attached floor plans (SK1 and SK2) stair plans (SK4) and stair section (SK5). A 3D diagram is also attached (SK3) to illustrate the concept, with each stair shown in a different color – please note walls and horizontal separations are not shown for clarity’s sake.

The proposed building has a relatively small footprint and is bound on 2 sides by a large public plaza. Interlocking exit stair shafts allow greater building efficiency, and allow an adequate number of residential units to make the development feasible.

The definition of a scissor stair assumes that there are two stairs in one enclosure, see below. The restriction of section 1015.2.1 is based on the presumption that there is only one enclosure as stated in the definition (stated below). We believe that if two separate enclosures are provided then limitation of section 1015.2 does not apply.

SCISSOR STAIR. Two interlocking stairways providing two separate paths of egress located within one stairwell enclosure.

The 2006 IBC commentary clarifies, "A scissor or interlocking stairway is sometimes used in high-rise buildings or to increase exit capacity of a stairwell enclosure. In this configuration, two independent stairway paths are located within the same exit enclosure and visually open to one another. When interlocking stairways are separated from each other with compliant fire barriers and horizontal assemblies, they are not considered scissor stairways (see Section 1015.2.1).”
Based on the proposed design and the excerpts from the code and commentary please confirm or clarify our interpretation that the proposed design meets the two exit requirement.

OSSC 2014 Section 1007.2.1

Elevators required. In buildings where a required accessible floor is four or more stories above or below a level of exit discharge, at least one required accessible means of egress shall be an elevator complying with Section 1007.4.

This is a 4-story building on a flat site. We are proposing an occupied roof, with accessible means of egress from the occupied roof provided by two interior exit stairways complying with Sections 1007.3 and 1022.

The occupied roof will not be covered or enclosed, and will not have a roof or walls over 48” high.

The building is equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1

See attached roof plan (SK6) and building sections (SK7).

OSSC 2014 Section 1007.4 requiring an elevator as an accessible means of egress does not pertain a four-story building with an occupied roof. An occupied roof is not considered a “story” or a “floor.”

The distinction between an occupied roof and a building “story” is clarified in the upcoming 2018 IBC. The approved language for the 2018 IBC states that occupied roofs are not considered a story if the deck does not have a roof or walls over 48” high (and clarifies that it is not subject to building height limitations).

By definition, a “floor” is the lowest walking surface of a room, and a room is contained within a story. An occupied roof is not considered an accessible floor.

See attached opinion from ICC on this subject (SK8 and SK9).

The reason Section 1007.4 is written this way (instead of stating that the requirement is for five-story buildings) is to provide for buildings that are on a sloped site.
According to the 2009 IBC code commentary for this 1007.2.1:
“On a flat site, “buildings with four or more stories above the level of exit discharge” would typically be a five-story building. The level of exit discharge is the first floor level, and the fifth floor is the fourth story above that. A story four stories below the level of exit discharge would be the fourth basement level. The verbiage is such that a building built on a sloped site can take into consideration that people may be exiting the building from different levels on different sides of the building (see Figure 1007.2.1).”

An elevator will be provided; however, it will not be on standby power as required by 1007.4 in order to be considered as the accessible means of egress. Providing standby power for the elevator would require the building to have a generator, which is prohibitively expense for this project.

2014 OSSC Table 503

Table 503 states that A-3 occupancies (roof deck) in Type VA construction may not be located higher than 3 stories above grade plane. (Increase to four stories above grade plane with automatic sprinkler increase per Section 504.2).

The proposed design meets the requirements of OSSC 503.1 since an occupied roof is not considered a story and allowed in the 2018 IBC. The protection measures provided are as follows: 

1. The occupied roof is 2,711 SF
2. (2) means of egress to (2) two hour rated stairways.
3. Emergency backup lighting to be provided for the egress path.
4. Fire extinguisher and standpipe provided at the exit stair enclosures.
5. Readily visible exit signage provided above the doors leading to the stairs.
6. Audible and visible fire alarm notification devices at the roof deck with manual pull station.

See roof plan (SK6)

The proposed design provides a limited area occupied roof that will be 2,711 SF in size, separated from the surrounding roof area by railings and raised garden areas, with an occupant load of 181 occupants per table 1004.1.2 and will meet the requirements of OSSC 1021.2. The occupied roof will be considered an A-3 occupancy, and is not a story per OSSC definition. The proposed design meets the applicable building code requirements of the ICC approved 2018 IBC model code lifting the restriction on locating roof decks above the maximum number of stories in fully sprinklered buildings. It is understood that this will roll into the new code cycle for the OSSC and is thus guidance only at this point but has been used to approve similar appeals. The approved language for the 2018 IBC also states that occupied roofs are not considered a story if the deck does not have a roof or walls over 48” high and clarifies that it is not subject to building height limitations.

The roof deck will meet the construction requirements of Type VA construction, with 1 hour rated roof assembly below the deck, and will not be provided with a roof structure. The occupied roof will be provided a fire alarm manual pull station and audible and visual alarm notification devices for notifying the occupants of an event in the building. The stair doors will have internally illuminated exit signs and emergency illumination fixtures will cover the roof deck and pathway to the second stairs. The deck will also be provided direct access to a standpipe connection and a fire extinguisher.

Two means of egress are provided from the roof deck. Both stair enclosures are 2 hour rated and meet the requirements of OSSC Chapter 10. The stairs will provide additional emergency personnel access to the roof by 2 stairs.

Section OSSC 3004.1

3004.1 Vents required. Hoistway of elevators and dumbwaiters with the hoist way height of 25 feet or more, as measured from the bottom floor landing to the underside of the hoist way ceiling, shall be provided with means for venting smoke and hot gasses to the outer air in case of fire.

Eliminate the vents entirely consistent with the 2015 IBC

The section on the hoistway has been eliminated from the 2015 IBC. Based on report from the ICC CTC Elevator Lobby Study Group (attached) there is a specific concern of smoke movement related to stack effect when these vents are incorporated in the design.

The building will be fully covered by an approved automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2

By eliminating the vents the stack effect is reduced and based on the attached ICC CTC study, this should improve the overall life safety and egress in the building.

Section 1812 Radon Control Methods R-2 and R-3 Occupancies

Radon Control Methods, R-2 and R-3 Occupancies

Section 18.12.3.7 – sub floor soil exhaust system ducts subfloor preparation. A layer of gas permeable material shall be placed under all concrete slabs and other floor systems that directly contact the ground and are within the wall of the living spaces of the building, to facilitate future installation of sub-slab depressurization system, if needed.

Section 1812.3.3 – Soil-gas-retarder. A minimum of 6mill polyethylene or equivalent flexible sheeting material shallb e placed on top of the gas-permeable layer prior to casting the slab or placing the floor assembly to serve as a soil-gas retarder by bridging any cracks that develop in the slab or floor assembly and to prevent concrete from entering the void spaces in the aggregated base material.

Section 1812.3.6 – Passive sub-slab depressurization system (basement or slab on grade). In basement or slab-on-grade buildings, sub-slab soil exhaust system ducts complying with Section 18.12.3.7 shall be installed during construction.

Section 18.12.3.7 – sub-slab soil exhaust system ducts (SSESD). SSESD’s shall be provide in accordance with this section shall run continuous from below the soil-gas-retarder to the termination point described in section 18.12.3.7.5

The Central Lofts building is a mixed-use building with a retail / restaurant on the ground floor and R-2 occupancy residential units on floors 2 through 4. The building structure will be wood framed walls, glulam columns and beams, and cross-laminated timber floors and roof.

There are no residential or living spaces on the ground floor level (slab on grade). All spaces on the ground floor level include mechanical spaces, retail, restaurant, residential lobby, bike room and trash/recalling rooms. These spaces are all mechanically ventilated and exhausted per chapter 4 and 5 of the Oregon Mechanical Special Code.

With the proposed system, all spaces between the slab-on-grade conditions and the residential/living areas on the 2nd through 4th floor will be mechanically ventilated/exhausted at a rate that exceeds that which is required for Radon Control with passive Sub-slab depressurization system.

We propose that the alternate design with the above-listed measures, including the code-compliant mechanically ventilated/exhausted spaces that separate all the residential/livings areas from the ground floor, exceeds the Radon Control requirements listed in Section 1812. We are proposing that the building will therefore not have the sub-slab depressurization system as described in section 1812