Venting: Is a Localized High Spot allowable?

My plumber created a problem with a low spot collecting water in my vents. I wonder if I can fix it by creating a high spot instead, which lets water drain out by gravity. The plumber said all vents have to be lower than the preceding one.

I am in a high-rise concrete building -- see diagram below. Vents are 1.5" copper, coming off a 3" cast iron stack in the corner. I have only one floor, so I have to stay within the 8' ceiling height I have.

My diagram shows a high spot in the middle of the array. Not at the stack. Does anyone with real life knowledge wish to comment? Am I missing something that could cause a future problem?

vent

I am not sure what you mean by a "low spot" or how you would cure it with a "high spot". As long as any water in the vent has a place to drain, in either direction, it will work, even though an inspector might not pass it. A more significant factor would be where the water is coming from.

Yes, hj, I see how knowing where the water is coming from is important.

In the diagram the big pipe on the left is the main vent stack for the entire building. My vents derive from this one, and I drew three of them. Between the second and the third the horizontal line jogs up a few inches before going horizontal again over to the third vent.

That is my "local high spot".

David

the water is most likely from condensation. according to the diagram the vent should drain. Technically speaking it is incorrect to have "backslope". Practically speaking it most likely won't be a problem unless enough water collects to deminish the venting area of the vent piping, which is unlikely unless you have a rather large sag or backfall.

so far so good

Sounds like no-one has any reason not to do it as shown above.

I called the plumber, and he agreed. But he has been known to disagree with himself at a later date.

vent

From your descsription and drawing, I cannot understand your original statement that water is collecting at the low spot. Your drawing shows vertical pipes that any water should drain to without collecting.

The drawing shows the future configuration that I was proposing

Hi hj,

You are right, that it is confusing... I could have added a sentence to say that instead of showing what was, I would show what will be. Sorry about that. I was asking fundamentally if my solution was going to work, and that is ultimately the most important thing. Not what was there and wasn't working right because it wasn't built right. At least that is the way I think. And I usually try to avoid saying things that are likely to be obvious because I don't want people to think I am talking condescendingly. So I didn't say it. And then I caused the opposite problem because apparently most people didn't understand the diagram as the proposed solution to the problem. So, by not saying what was to me obvious I then caused another communication problem. Agh.

Reverse the high spot into a low spot (in your mind) and you will have the old way it was. The plumber was trying to avoid an obstacle. The vent was supposed to slope downwards, and it actually did look like it in this small space bathroom where every view made it look like it was properly sloped. Of course he did not want to make me lower my ceiling height by too much either. It's a tight space.

Anyway, that is all gone now. Last night I redid it all. The horizontal section now goes up and over the obstacle. Water will slide down the little slope I put in this horizontal piece and go into the last down-piece of the venting system. When I call it "horizontal" I know that is not the right term truly since it is slightly sloped. Hope you understand.

Lessons learned: in a concrete condo apartment building with 8' ceilings, always build your vents to go up and over other pipes, even if it means your venting system will have some isolated high spots -- ASSUMING of course that water can still drain down into drains on BOTH sides of the high spot. Hope this is clear. Hope this helps future DIY condo renovation and remodeler people.

Lessons learned: always be ultraclear. No matter whether it is already obvious.

David . - --- P.S. I may post a picture in a few weeks when I get the film developed.