If your home has less or extra plumbing fixtures like water closets, lavatories etc than required, how do you feel about that?
Disgusting ! Right?
Yes, it is. As per regulation of International Building Code (IBC), minimum number of fixtures are must for every type of building. On the other hand, the number of plumbing fixtures affect the design of a building.
So, Required plumbing fixtures calculation must be accurate. Over or under calculated plumbing fixtures might cost extra money or bring distress for you.
That’s why you have to get the answer to how to calculate plumbing fixture count. In this article, we will find the answer step by step with relevant examples.
Why do you need to know plumbing fixtures calculation?
- To follow the regulations of IBC and IPC
- To avoid unexpected situation
- To set up a plumbing system in a building.
- To avoid unnecessary costs
If you are a designer or a homeowner, you need to know about some information on plumbing. To set up a plumbing system you have to know about plumbing fixtures.
All plumbing fixtures and installations are required to be designed and installed in compliance with specific state’s plumbing code and building code as well.
Determination of the number of plumbing fixtures
Minimum number of plumbing fixtures for a building shown in International Plumbing Code (IPC) 2018’s table 403.1.
The required number of plumbing fixtures depends on occupant load for all areas. Here comes International Building Code. IBC to determine number of occupant.
First, you have to calculate the number of plumbing fixtures required which is dependent on the occupant load for all areas.
The required number of plumbing fixtures must be based on two areas like indoor and outdoor areas.
It’s important to consider the outdoor area because that area is used by residents in addition to the residents staying inside a building.
Step 1: Determine the Type of Building
At first, you have to find out the type of building required to calculate plumbing fixture count. To do that go to codes.iccsafe.org for 2018 international plumbing code. There in Chapter 4 (FIxtures, Faucets, and Fixture Fittings), you will find a table called TABLE 403.1 —continued MINIMUM NUMBER OF REQUIRED PLUMBING FIXTURES.
From that table you have to determine the building type. To do that just check column name description. Here you will find Gaming areas, Auditoriums without, permanent seating, art galleries, exhibition halls, museums, lecture halls, libraries, arcades and gymnasiums etc.
From those buildings match your building type say our example 1 building type is Retail Store.
Step 2: Occupant Load Determination
To determine the total occupant load will be determined as per Occupant Load Factor International Building Code’s regulation.
Step 3: Occupant Load Breakdown
This time a question comes forward that is what determines the number of males and females?
It’s simple. Just divide the total occupant load in half. For calculation of occupant load, you should assume 50 percent male and 50 percent female.
One thing you have to remember is that the required water closets for females should not be less than required water urinals and closets for males.
Step 4: Calculation (Method for Mixed Use Buildings)
You can calculate the required number of plumbing fixtures by following 2 different methods.
1. Standard Method:
For determining the required number of fixtures for each use, assign each area an occupant load per table of IBC and then use states plumbing code. Consider all required fixtures for all uses.
2. Fractional Method:
First, assign the area of occupant load per table. After that divide calculated occupant load by the allowable fixtures per person in states plumbing codes.
To calculate the total number of plumbing fixtures, you have to accumulate all the area use fractions. You should round up to the nearest whole number.
Example to calculate plumbing fixture count
Now we will learn how to calculate plumbing fixture count by 2 examples. There 2 types of simple ratio will be applied.
In example 1, ratio applied equally to both males and females, and Example 2 uses other ratios.
In example 2: first, divide the total occupant load by 2 or get 50 percent. Then apply the ratio to male and female load.
On the other hand in example 1, First, apply the ratio to the total occupant load. Then divide the number of fixtures between female and male.
Note: we rounded up fixture count numbers to the next whole number.
Example 1: A Retail Store with 2,000 total occupants.
Calculation of Closets
Water Closets: ratio 1 per 500 (As per IPC 2018’s Table number 403.1 )
2,000 x 1/500 = 4 water closets
4 x 50% = 2
2 water closets for males
2 water closets for females
Calculation of Fountain
Drinking Fountains: ratio 1 per 1000 (As per IPC 2018s Table number 403.1 )
2,000 x 1/1000 = 2 drinking fountains
Calculation of Lavatories
Lavatories: ratio 1 per 750
2,000 x 1/750 = 2.66
2.66 x 50% = 1.33 = 2
2 lavatories for males
2 lavatories for females
Example 2 – A theater with 1,155 total occupants
Calculation of Closets
1,155 x 50% = 577.5
Water Closets: ratios 1 per 125 (males) and 1 per 65 (females) (As per IPC 2018’s Table number 403.1 )
Males: 577.5 x 1/125 = 4.62 = 5 water closets
Females: 577.5 x 1/65 = 8.88 = 9 water closets
Calculation of Lavatories
Lavatories: ratio 1 per 200 (As per IPC 2018’s Table number 403.1)
Males: 577.5 x 1/200 = 2.89 = 3 lavatories
Females: 577.5 x 1/200 = 2.89 = 3 lavatories
Drinking Fountains: ratio 1 per 500
1,155 x 1/500 = 2.31 = 3 drinking fountains
Here we illustrate another method of calculation used by IBC to calculate fixture counts is the graduated ratio.
Under this method one ratio is used for the first section of Occupants and another ratio for other Occupants numbers. It’s called the Graduated method which is used for the water closets and lavatories.
Example 3: Office building with 250 total occupants
Water Closets: ratios 1 per 25 for first 50 and 1 per 50
for remainder exceeding 50 (As per IPC’s Table number 403.1)
50 x 1/25 = 2 water closets
(250-50) x 1/50 = 4 water closets
2 + 4 = 6 water closets
6 x 50% = 3 (3 water closets for males and 3 water
closets for females)
Calculation of Lavatories
Lavatories: ratio 1 per 40 for first 80 and 1 per 80 for
remainder exceeding 80 (As per IPC’s Table number 403.1)
80 x 1/40 = 2 water lavatories
(250-80) x 1/80 = 2.13 water lavatories
2 + 2.13 = 4.13 water lavatories
4.13 x 50% = 2.06 = 3 (3 water lavatories for males
and 3 water lavatories for females)
Calculation of Fountains
Drinking Fountains: ratio 1 per 100 (As per IPC’s Table number 403.1)
250 x 1/100 = 2.5 = 3 drinking fountains
Fixture Count Calculations for Mixed Occupancies
We know the IBC edition before 2009 didn’t have any explanation about how to calculate plumbing fixture count for buildings with mixed occupancies.
The major confusion is on how to act the fixtures to calculate the total number of fixtures.
Under this typical method to get total fixture count it accumulates the rounded fixture numbers for each occupancy group.
Rounded fixture count has a con. Sometimes it causes additional fixtures which are not intended.
Though it’s not an issue from a public and a building departments point of view. But it’s a real problem from a design professional and an owner’s perspective.
Additional fixtures have some drama back say For example it’s required extra money as well as extra space.
That’s the reason why a professional needs to know. How to calculate plumbing fixture count.
By getting the information a design professionals intention to provide an exact amount of fixtures. This will give you safeguard and safety as well.
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