Plumbing fixture count in existing buildings.

[mschirmer]

I'm curious about the interpretations of the code listed below. How is an increase of 20% work? Is that from a specific date? We use this code all the time whenever we are adding another tenant to a floor in order NOT to increase the restrooms. We will get the original occupant load for the spaces from the city, and get the difference from the new space(s) to set the percentage. Doing this, the odds are very low that we will ever cross the 20 percent threshold, although with 2018/21 the percentages do get closer to 20%. So I'm curious how this is actually supposed to be interpreted.

2015/2018
INTERNATIONAL EXISTING BUILDING CODE: SECTION 809.1 (2018) / 810.1 (2015)
WHERE THE OCCUPANT LOAD OF THE STORY IS INCREASED BY MORE THAN 20%, PLUMBING FIXTURES FOR THE STORY SHALL BE PROVIDED IN QUANTITIES SPECIFIED IN THE INTERNATIONAL PLUMBING CODE BASED ON THE INCREASED OCCUPANT LOAD.
2021
INTERNATIONAL EXISTING BUILDING CODE, SECTION 1009.1 EXCEPTION: ONLY WHERE THE OCCUPANT LOAD OF THE STORY INCREASED BY MORE THAN 20%, PLUMBING FIXTURES FOR THE STORY SHALL BE PROVIDED IN QUANTITIES SPECIFIED IN THE INTERNATIONAL PLUMBING CODE BASED ON THE INCREASED OCCUPANT LOAD.

 

[RLGA]

When I am in this situation, this is how I handle it, especially if the building had no design occupant load determined.

Step 1: Determine the occupant load of the existing building before alternations using the currently adopted building code.
Step 2: Determine the occupant load of the existing building after alterations using the currently adopted building code.
Step 3: Use the following calculation: [(OLa - OLb)/OLb] x 100 = PI

Where:​

OLa = Occupant Load after alteration​

OLb = Occupant load before alteration​

PI = Percent increase​

Step 4: If PI > 20%, then provide the number of fixtures per the IPC. If PI ≤ 20%, then the number of existing fixtures is adequate.

 

[Tim Mailloux]

When I am in this situation, this is how I handle it, especially if the building had no design occupant load determined.

Step 1: Determine the occupant load of the existing building before alternations using the currently adopted building code.
Step 2: Determine the occupant load of the existing building after alterations using the currently adopted building code.
Step 3: Use the following calculation: [(OLa - OLb)/OLb] x 100 = PI

Where:​

OLa = Occupant Load after alteration​

OLb = Occupant load before alteration​

PI = Percent increase​

Step 4: If PI > 20%, then provide the number of fixtures per the IPC. If PI ≤ 20%, then the number of existing fixtures is adequate.

this is exactly what I do as well.