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How to use NSPS 2015 - 7.21.10 - "fractions" of required fixtures

Jay

Jay

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Joined
Apr 8, 2018
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87
Location
NJ, USA
Hello. I have a mixed use building and my fixture count, per each of the three occupancy types, seems to come up a little high. Just using real world experience here...I just can't picture this men's room needing (4) water closets. This is preliminary and my figures are rough...just trying to get an approximate count so I can allot the appropriate space for the restrooms.

As an example...

I have a Business Occupancy totaling 56 persons. Divide that by 2 and we get 28 persons of each sex. Thus I need (2) water closets and (1) lavatories for each sex for a total fixture count of (4) water closets and (2) lavatories.

Factory Occupancy totals 12 persons / 2 = 6 persons each sex. Thus (1) water closet and (1) lav for each sex for a total fixture count of (2) water closets and (2) lavs.

Finally, there is Storage area. 4 persons / 2 = 2 persons each sex. Thus (1) water closet and (1) lav for each sex for a total fixture count of (2) water closets and (2) lavs.

My grand total here is (8) water closets and (6) lavs. Or for each sex, (4) water closets and (4) lavs...Just seems slightly high to me. As I look at 7.21.10 I wonder if this could apply as a way to reduce the fixture count. "Where the number of persons for each sex is less than 100% of a particular group (Yes, this is the case since I am using 50% of the total to apply to each sex) the number of fixtures required for that group may be reduced by the fraction of the persons in that group" (wondering if I can divide by 50% since that is the fraction, or percentage as I am using it, I have reduced the total persons of each sex.). Is this the intent of 7.21.10?

I have searched the forums....found some good info on calculation fixture counts, but nothing regarding the intention of 7.21.10.

As always, your experience is much appreciated. Thank you,
Jay
 
Not sure where you are getting your numbers or what the NSPS is. But you are right, that is too high. I will use w/c as an example from 2012 IPC t403.1:
B=1.12
F=.06
S=.02
Add 'em up (IPC 403.1.1) =1.2 then round up to 2 for each gender.

I can't imagine other codes would be that different......but sometimes I get accused of having no imagination.
 
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I don't know what the NSPS is either lol, but I'm sure it's something! That was a typo.

I'm getting my numbers from table 7.21.1, fixture requirements NSPC 2015, which is what is used here in NJ.

Your figures seem low to me. How bout we meet halfway with three of each and call it a day?
 
Thanks for the chart Francis. Unfortunately I can not open or read it. I've tried clicking it several times and I keep getting an error message.

I'll try again tomorrow. Appreciate your input.
 
this is what I'm getting...

The Building Code Forum - Error
You do not have permission to view this page or perform this action.
 
Jay, I was able to view the picture after I loggin; perhaps that's a benefit of paid members.

Here's the link of what I posted; an Excel Express calculator: http://ara4help.com/About_Us.html

In the example Sifu provided are fractions for each type of occupancy and summed for the total. Keep in mind the calculations can be varied when a family (unisex) accessible water closets are included as part of the count depend on your state, local code and the AHJ.

Business - 56

56/2 = 28 for each gender

For the first 50 males, the ratio of 1 per 25 is applied:
28 x 1/25 = 1.12 water closets (note Sifu answer above).

For the remaining number of males, the ratio of 1 per 50 is applied: if it were more than 50 - 50 x 1/50

At this point the fraction is not rounded up, the IBC provides the following guidelines;

"For calculations involving multiple occupancies, such fractional numbers for each occupancy shall first be summed and then rounded up to the next whole number."
 
Last edited:
Jay said:
this is what I'm getting...

The Building Code Forum - Error
You do not have permission to view this page or perform this action.
Click to expand...

Thats what I get too, but I am a paid member.
 
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