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Sizing of drainage system

steamer45 Member Posts: 13
I am requesting input from anyone, preferably a Mechanical engineer, for comments on a small new build project I am involved in. It is a medium sized auditorium seating approximately 100 people with 1 men's & ladies restroom. Total plumbing fixtures are 6 - 1.6 gallon, gravity flush, tank type water closets, 2 wall hung urinal's, 4 standard counter top lavatories (0.5 gal flow) 1 standard laundry tub, 3 - 3"floor drains and condensate from 2 - 10 ton roof top hvac units. The sanitary building drain is 4" pvc connecting into a 6" pvc building sewer. The length of this sewer is approximately 100' to the municipal manhole. Would there be some concern about the sizing of this main in relation to the expected flow, perhaps insufficient to evacuate all of the solids. Building usage is expected to be 3- 5 hours at a time 2-4 days per week. Total fixture unit load is estimated at 34 dfu (State of Michigan 2015 plumbing code).


  • Jamie Hall
    Jamie Hall Member Posts: 22,162
    Shouldn't be a problem if there is adequate slope on the drains. Modern low flush WC's (like you have there) can sometimes give trouble if there isn't enough slope.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England