When the great fire swept through Rome in 64, Nero was at his vacation villa in Antium, hours away. By the time he reached the city, the entire place was ablaze. Only four districts out of fifteen were spared, although some historians say only 1/10th of the city was actually destroyed. Never the less, Nero quickly organized a relief effort including opening up palaces to house the homeless. He also implemented strict fire codes which no longer allowed houses to be built on top of other houses or too close to each other. Streets were made wider (60′) in order to stop easy flame spread. He even installed ceiling fire sprinklers in his own palace.
Today we have the Uniform Building Code (and others such as BOCA) which is primarily concerned with fire. In this blog entry I will, in now way, try to give advice about an actual space. I just want to give a quick overview of how the codes work, not any particular code relevancy.
The first thing you have to determine is the building type. Let’s say it is a concrete block building with steel structure, like a typical strip mall. We’ll also say that you want to put a store into this building. The building type would be considered “non-combustible” because steel and concrete doesn’t catch fire. In keeping with this, you wouldn’t want to build walls inside using wood studs; you’d want to use steel studs to keep with the whole “non-combustible” thing.
The second thing to determine is the building use. This is important because different types of use change how the code is applied. If it is a movie theater, for instance, you can cram an awful lot of people into a space, whereas a store won’t have as many people at any given time. For this exercise we’ll stick with the store, known as occupancy type M for Mercantile.
Now that we know the occupancy type we can determine the occupancy load. This is important in order to determine how many exits we will need, how wide they need to be, etc. For a mercantile space the occupancy load is given in three parts: the main sales floor and basement which has a load of 30 gross; other floors (other than a mezzanine) has a load of 60 gross; and the storage or stockroom with 300 gross. Gross means the total area of the floor including walls and columns and stuff; in other words, you don’t subtract anything. If the area was NET, then you’d subtract to get the actual floor area.
So, let’s say the space is 100 feet deep x 25 feet wide. The sales floor takes up the first 80 feet of depth and the stock room, office and restroom take up the back 20 feet. That would mean the area for the sales floor is 2000 square feet divided by 30 = 67 people can occupy that space. The stockroom is 20 x 25 = 500 square feet, divided by 300 = 1 person, maybe 2 can get away with being back there at any given time.
Now that we know the occupancy load, we can figure out how many exits we will need. For areas that hold more than 50 people, we will need two exits, at opposite ends. We can figure out how wide the exits need to be by multiplying the occupancy: 67 by an egress factor, also found in the UBC. The factors are a number for stairways and exit doors for buildings with sprinklers, and buildings without sprinklers. Let’s say our building will have sprinklers. The factor for such a building is 0.3 for stairways (which we don’t have) and 0.2 for other egress (exits). So, we have 67 people +1 in the back room, so a total of 68. 68 x 0.2 is only 13.6 inches wide. However, no exit door can be that narrow so we have to make them a good width of 36 inches. If we had a space with perhaps 400 people, we would need 80 inches of exit width (nearly seven feet).
I’d like to close this entry by restating something that keeps coming up all the time. I will do an exit calculation for a space and the client will say, “oh, we’ll just get a variance for that so we won’t need so many doors”. Variances are only given for local ordinances and cannot be given for the Uniform Building Code. No matter what. And, even if the local Fire Marshall or code inspector or city official, or whomever, ends up approving the building or giving a “variance”, the architect, client, etc. will be responsible if something happens. The insurance company won’t cover incidents where there were obvious code violations. Just keep it in mind, there is no such thing as a variance to Health and Safety codes.
