Combining drainage stacks 1

[EnOm]

Hi
I was wondering why I never see anyone combining drainage stacks. What is the logic behind it?
What I mean is:


[li]DWV System[/li]
[li]10 storey building and I have fixtures on both sides of the building[/li]
[li]One 4" waste stack on each side for the sake of explanation. Both with an attendant vent stack.[/li]

If I were to combine both on the third floor so that they both "pour" into one 6" stack. The vent stacks will also be combined into a larger vent stack.

What problems would arise from this?

Regards

 

[PEDARRIN2]

If the stacks are located in good areas to bring down, i.e. near columns, shafts, etc., there is typically no need to combine them. To combine them, you have to run horizontally above the ceiling or exposed, slope the pipe so it drains, which means you can only go so far before you are below the ceiling or hit a duct.

Once you get below the slab, you typically only have to worry about missing/coordinating with structural elements and your final invert.

If the underground invert is an issue, you can "step" the stacks by offsetting each toward each other on each floor level, like going from column to column until they meet at a lower floor. That typically works as long as the ducts are small and the architect will give you an enclosure around the column to hide the pipe.

Depending on what code you are using, you may have some additional venting requirements since you are more than 5 branch intervals and approaching 10 branch intervals. You can mitigate this with the offsets and sizing of the pipe if you are in the IPC arena.

 

[hvacpiper]

Offsetting of sanitary stacks should always be avoided in IPC land on structures with more then 5 branch intervals. The often overlooked ,sections 711 and 915 of IPC come into play, which severely limit connections around offsets,and typically add more floor penetrations due to increased number of vents..

Cost and coordination would be a factor as well,as it's fairly easy to find ,or get the architect to give you a 6" stud wall to run a 4" riser in.Chases for 6" pipe, are usually harder to come by, in this day and age of the architects designing to use every square inch of a building.....

 

[EnOm]

Thank you for your responses and suggestions.
As for offsetting the pipes there shouldn't be any problem as it is architect's suggestion to combine the drainage stacks since he wants to reduce the number of shafts on the floor.

The building is actually a hotel and there are a total of 14 drainage stacks coming down from the room floors to an event area with large halls...etc. The architect wants to reduce the number of shafts as much as possible so as to not ruin the large open spaces and thus suggested combining the stacks where possible, and is willing to facilitate this proposal by increasing floor height to be able to accommodate the slopes..etc.

What I understand is that there is are no objections, plumbing wise, to combining drainage stacks, as long as the pipes are sized correctly and ventilation requirements are met. It just needs to be facilitated properly in terms of space, ceiling height...etc. Is this correct?
What had occurred to me was that combing them would cause flow problems, ventilation problems, and such.

Thank you again for being so helpful


Regards.

 

[PEDARRIN2]

If the architect is providing enough space above the ceiling, then there are no issues, as long as you size per the codes and put in the required venting on the stacks.

Have you considered using Sovent for the room drainage stacks? I used it on a hotel project and it eliminated a lot of the venting in the rooms.

http://sovent.com/

http://www.proventsystems.com/?page_id=952

 

[EnOm]

PEDARRIN2,
Thank for your help. I will also take a look at those links.

Regards