Septic Tank Design for an Office Complex





Septic Tank Design Calculations | Building Construction

In the previous article, we discussed in detail the calculations that are to be carried out for the design of a Septic Tank for 3bhk, 2bhk and 1bhk homes.

In this article, we will move forward with our discussion on the Septic Tank calculations for an Office Complex.

First question that is likely to occur to your mind would be, “How are Septic Tank Design calculations for an Office Complex different from that of a Residence?”

Let us first answer this question before we move forward with the calculations.

Residences are structures which are occupied with families living, eating and sleeping there. Let’s take an example of a person who regularly goes to an office for his job.

Let’s have a look at his Daily schedule:

  • He wakes up in the morning.
  • Takes a bath, uses a toilet.
  • Has his breakfast after which he washes his hands. Apart from him using the services in the house, his family members also use the same.
  • He leaves for his office. After he reaches the office, he wouldn’t take bath which consumes the maximum amount of water which turns into sewage water after use.
  • His usage of toilet and bathroom would be minimum. Hence, it is important to understand the logic behind the Septic tank calculations.

Calculations for an Office Complex with 8000 employees

As per thumb rule;

Quantity of sewage to be considered for an Office Complex is to be calculated on the basis of the capacity of the Office.

Now, we are calculating the Volume for the Septic Tank required for an Office Complex with 8000 employees.

Hence, quantity of sewage to be considered per person should not be less than 20 gallons.

Office Complex = 8000 persons

Total quantity of sewage = 8000*20 = 1,60,000 gallons

1 gallon = 3.78 litres

Quantity of sewage in litres = 1,60,000 x 3.78 = 60,4800 litres

Volume of Sewage in cubic metres:

60,4800/1000 = 604.8 cubic metres

Volume of Sewage in cubic feet:

604800/28.52 = 21206.17 cubic feet

Dimensions of a Septic Tank for an Office Complex in Metres:

Length of the Septic Tank = 15m

Width of the Septic Tank = 13.44m

Depth of the Septic Tank = 3m

Dimensions for a Septic Tank in Feet:

Length of the Septic Tank = 49.5’

Width of the Septic Tank = 44.352’

Depth of the Septic Tank = 9.9’



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  1. #1 by Nazar Ahamed on October 7, 2011 - 4:29 am

    Hi benzu 🙂

    Volume of Sewage in cubic feet:
    604800/28.52 = 21206.17 cubic feet

    here what is 28.52…????

    • #2 by BenzuJK on November 28, 2011 - 8:37 pm

      It is a conversion factor from litres to cubic feet.

      Cheers:)

    • #3 by wajid on November 17, 2012 - 8:54 am

      1cubic feet is equal to 28.52 litter

  2. #4 by ronnie orense on April 21, 2012 - 6:01 pm

    thanks a lot for all the vital info!!!!

  3. #5 by Eunice on May 15, 2012 - 11:04 pm

    how did you get the length, width and depth?

  4. #6 by JOSEPH MUREITHI on June 15, 2012 - 9:13 am

    these information is very useful.

  5. #7 by dayana vincy on August 29, 2012 - 12:54 am

    to convert cum to cft ,multiply by 35.31.here they have divided (1/35.31).

  6. #8 by Saumik Mallick on October 14, 2012 - 9:28 am

    Mam please explain in what basis we consider the dimension of the Septic Tank

  7. #9 by MEHUL PANDYA on August 10, 2013 - 12:08 am

    here CM to CFT conversion use 28.52-I think 1CM=35.36 FT am i right?

  8. #10 by S Das on August 7, 2016 - 8:46 pm

    Wht about soak pit

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