The IBC (International Building Code) and the IPC (International Plumbing Code) provide prescriptive requirements to calculating the minimum number of plumbing facilities needed in a building, including toilets, sinks, & drinking fountains.
Calculate Occupant Load
First you need to calculate the number of occupants for a space. The occupant load table in chapter 10 of the building code show the square feet per occupant based on the function of the space. Please see the table below:
So, let go through an example of a bar/ tasting room that is 1,000 SF.
If there is loose, non-fixed furniture, we would use the occupant load factor above of 15 net sf.
The difference between net & gross is that net sf does not include unusable areas such as wall depths, hallways, etc…whereas gross sf includes all areas of the building. If you have a fixed bar in your tasting room, that area can be discounted from the net sf.
1,000 / 15 = 67 occupants. Simple as that! Of course, these calculations can get much more involved when you begin to have multiple functions of space, etc. Hint… the back of the bar where customers do not go can actually be counted as a business occupancy, which is a different factor of 100 sf per person!
Calculate Minimum Number of Plumbing Fixtures
Now we have determined that we have 67 people. Lets figure out how many bathrooms that equates to.
We go to Table 2902.1 in the IBC (or Table 403.1 in the IPC) to resolve the minimum plumbing fixtures required. The table takes into consideration the occupancy, and a more descriptive use of the space for these purposes. Check out the chart below:
For a bar, we would simply go with the A-2, Bar category. The Water Closets (Toilets) are required to be 1 fixture per 40 people, of each sex. So, We have 33.5 Males, and 33.5 Females. 33.5/40 is .84, so we are required to have 1 toilet for each sex. In most cases, you are required to have separate facilities for each sex (i.e. a separate mens room and womens room), but there are a few exceptions. If there are less than 15 occupants, a shared bathroom can be used.
The lavatories (sinks) would be 33.5/75= .45, which would also just round up to 1 sink for each sex.
The occupant loads and bathrooms can be a critical consideration when designing or remodeling a facility. If you are on the cusp of going over 1 toilet for each sex, that could mean totally different and larger bathrooms. About 80 occupants (40 male and 40 female) would be the threshold to stay under to keep it at 1 toilet for each sex. That translates to approximately 12oo sf for a tasting room area.