Performance Method - Allowable Area Calculations

[NCRooster]

I am working through the performance method parameters for an early 1900s historic downtown building. We typically use the work area method, but unfortunately that won't work for this building. The building has 3 stories + a basement, 48' height, with S-1 in the basement, M on the ground floor, B on the second floor, and R-3 (two units) on the top floor. S-1 and M are nonseparated. B and R-3 are separated by 1 hour floors and walls. The ground floor is 3000 SF, all other levels are 1500 SF each. The ground floor (M) is the only occupancy in our scope - it was previously an art gallery, so change of occupancy plus some MEP work. Exterior walls are 24" masonry. Building type is III-B and all floors are sprinklered. I am using the NC 2018 EBC, which is based on the 2015 IEBC.

The building is well within the allowable area for each level, so I'm not concerned, but I do need to work out the exact number of points for this parameter. The snag I'm hitting is that I need to divide actual area by allowable area for each occupancy (per NC EBC 1401.6.2 and its subsections), but R-3's allowable area is unlimited. How do I work "unlimited" into the formula? Am I missing something simple here?

 

[NCRooster]

Unfortunately it doesn't look like the performance method is workable for our project due to severe egress issues with the existing building that offset all of the other numbers. This is a long skinny building with properties on three sides, so no way to add a second exit or reduce the travel distance other than by adding a long corridor that would render the already very narrow space unusable. I would be fine adding in the corridor of course, but I doubt the building owner will go for it. I am going to see if the fire marshal will consider the prescriptive method instead.

That said, I would still welcome input on my question for learning's sake. In this specific example, would I disregard all levels outside of the area of work and just focus on the ground floor, which is M? And if the entire building were being renovated (so that there is no way around the R-3 issue), what then? Would I calculate each level separately, with the R-3 being assigned the maximum possible value (11.5 in our case), and then average out the levels for the final number?

 

[steveray]

Interesting....

 

[LR419]

The building is well within the allowable area for each level, so I'm not concerned, but I do need to work out the exact number of points for this parameter. The snag I'm hitting is that I need to divide actual area by allowable area for each occupancy (per NC EBC 1401.6.2 and its subsections), but R-3's allowable area is unlimited. How do I work "unlimited" into the formula? Am I missing something simple here?

x/∞ = 0.