number of exits for a multistory multifamily building

[drubinoff]

Hi,

I'm working on a small mixed use building in Massachusetts. The existing second story will be converted to residential (two apartments) and a new third story addition will be built for an additional one or two apartments.

The existing second story has two means of egress. The building will be fully sprinklered.

I'm reading in IBC 2009 that Table 1021.2 allows for the second story to have one means of egress in our case (R-2 occupancy) and the third story to have one means of egress in our case (R-2 occupancy with sprinklers). Therefore, it's my interpretation that each unit only needs access to one egress stair. Another way of interpreting this is that the two third floor apartments would could share a common stair (outside the units) down to the second floor.

I would have thought the third floor would have had to have had two means of egress and have every unit have access to two means of egress, but I guess that's not the case here.

The situation is muddied by the fact that the rear of the building (which is part of a continuous block of buildings sharing party side walls) has the basement at grade; I suppose it could be argued that the rear of the third story is actually a fourth story, and would need a second means of egress for both the story and for both units on that floor.

In particular, I'm trying to understand on the third floor if I need (a) the second stair and (b) if so, whether I need to surrender square footage to a connecting corridor between stairs.

Thoughts? Please argue with me.

Thanks,

Derek

 

[cda]

Well thought out plan

Sounds good, a little hard to make a call without seeing a plan

 

[mtlogcabin]

4 dwelling units and 50 feet travel distance

Do you meet the 50 ft travel distance from the 3rd floor? If you do I think you may be good.

1016.1 Travel distance limitations.

Exits shall be so located on each story such that the maximum length of exit access travel, measured from the most remote point within a story along the natural and unobstructed path of egress travel to an exterior exit door at the level of exit discharge , an entrance to a vertical exit enclosure , an exit passageway , a horizontal exit , an exterior exit stairway or an exterior exit ramp ,

 

[drubinoff]

Thx. The overall building length is 92' (and its width is 25'), so we might just make that travel distance, especially on the third floor where our floor plate will actually be smaller than that (due to front and rear zoning setbacks for new construction). So, if the stair comes up to the middle of the third floor unit, perhaps we are OK? I'm assuming outdoor unenclosed decks at the front and rear would not need to count for that travel distance.

I am, however, unsure if the City would consider the additional floor a third story or a fourth story as, while it is the third story from the front, the rear alley is actually at basement level. Keep in mind the side walls are shared with neighboring buildings.

Thanks,

Derek

 

[mtlogcabin]

unsure if the City would consider the additional floor a third story or a fourth story

You may meet building code definitions but not zoning. It took a few years but we finally got the zoning definitions to match the building code except for Townhouses. Zoning still requires a property line between units which I agree with since that was the original requirement in the legacy codes.

BASEMENT. A story that is not a story above grade plane (see "Story above grade plane " in Section 202).

STORY ABOVE GRADE PLANE. Any story having its finished floor surface entirely above grade plane , or in which the finished surface of the floor next above is:

1. More than 6 feet (1829 mm) above grade plane ; or

2. More than 12 feet (3658 mm) above the finished ground level at any point.

GRADE PLANE. A reference plane representing the average of finished ground level adjoining the building at exterior walls . Where the finished ground level slopes away from the exterior walls , the reference plane shall be established by the lowest points within the area between the building and the lot line or, where the lot line is more than 6 feet (1829 mm) from the building, between the building and a point 6 feet (1829 mm) from the building.

 

[drubinoff]

Thanks. So, if the first floor is not always 6' above grade plane (for instance, it's at grade at the front and it's impossible to say about the sides given the side walls are party walls), and the finished first floor is 11'-6" above the basement finished floor, we might be OK with it being still considered a "basement"?

The "grade plane" definition doesn't help so much as the grade is flat in front and at rear of the building 6' out. The average grade based on my description is exactly between the basement and 1st floor....