Can vent go downward below the highest fixture?

**keano016** · 03-11-2011, 12:59 PM

Might seem like a silly question, but please bear with me.

I know that venting must go vertically up 6 inches above the highest fixture, which is usually the sink prior to going horizontally.

My question is, once I go vertical, let's say 20inches above the rim of the vanity, can I go horizontal for a foot or so, then go downwards vertically for 30 inches, and connect to a vent?

**Basement_Lurker** · 03-11-2011, 01:07 PM

No you can not.

**Tom Sawyer** · 03-11-2011, 01:51 PM

It will trap condensation and over time will seal off the vent.

hj · 03-11-2011, 05:17 PM

It will work because condensation will drain both ways, but I doubt that you would ever find an inspector who would approve it. They usually only know what is "in the book" and cannot visualize how anything else would work properly.

**keano016** · 03-12-2011, 05:22 AM

Here is my situation. The bathroom is in a dormer in the attic that has one wall that is an outside wall but there is a 2 feet crawl space on the bottom. So I was thinking of wenting from the sink go up then down then around to connect to the 2 inch meta venting that goes to the roof.

What would you do?

**cacher_chick** · 03-12-2011, 07:19 AM

I cannot make sense of the drains in your drawing, but it appears that the lav can be vented into the 3" CI or go straight up through the roof.

**keano016** · 03-13-2011, 08:10 PM

Yes, the cast iron is there, but I am nor sure how I can tap into the cast iron, especially since there are two cast iron pipes connected there, one 3 inch that is the drain from the toilet plus a 2 inch that is a vent from the lower floors.

I want to avoid going through the roof because of the fear that I may not do it properly and then there is a leak or I fall

if I can go around the small wall, which requires going below the highest fixture, then I can connect to the 2 inch metal venting on the oposite wall.

**cacher_chick** · 03-13-2011, 08:32 PM

Originally Posted by keano016

if I can go around the small wall, which requires going below the highest fixture, then I can connect to the 2 inch metal venting on the oposite wall.

You cannot go down with the vent.

Because you don't know how to do something right is never a good reason to do it wrong.

**dlarrivee** · 03-13-2011, 10:01 PM

The "proposed vent" on your drawing doesn't make any sense at all...

You're going to have a tough time tying into the 3" CI stack at the proper height, so your best bet is to go through the roof... It's not a big deal...

**keano016** · 03-13-2011, 10:04 PM

I agree. That's why I was asking, altough I kinda expected you guys will say no to going down below the fixture. I still do not see the problem thou.

**Cubey** · 03-13-2011, 10:08 PM

This (I think) would be the correct way of sharing a vent (the red line). So why is it you can't do it that way? It might need to be higher than I placed it but that's the general idea.

**keano016** · 03-13-2011, 10:13 PM

Originally Posted by dlarrivee

The "proposed vent" on your drawing doesn't make any sense at all...

You're going to have a tough time tying into the 3" CI stack at the proper height, so your best bet is to go through the roof... It's not a big deal...

Seems the easiest way to go through the roof. One thing I have not drawn out on the picture is a plastic vent through the roof from a high efficiency furnace. Now, the guys who did it they connected the fresh air supply and the venting together to a wye and then one 3 inch pipe is going through the roof. Is that set up ok (mixing the supply and the condensation vent? If so, can I tap into that with the sink vent since it is plastic and easy to work with?

**keano016** · 03-13-2011, 10:14 PM

Originally Posted by Cubey

This (I think) would be the correct way of sharing a vent (the red line). So why is it you can't do it that way? It might need to be higher than I placed it but that's the general idea.

That is a Cast Iron 3 inch vent so it is challenging to connect to.

**Cubey** · 03-13-2011, 10:23 PM

Does it have a tee currently where I am showing the red line tapping into it? If so, could you not remove the tee and plus a 4-way ( + ) one? And anyway, your proposed vent had it going over there anyway to that exact spot. I just cut out the extra wasted amount going up, across and back down.

**keano016** · 03-13-2011, 10:31 PM

sorry about the confusion in the drawing. A 2 inch cast iron ties with a 45 degree tee into the 3 inch cast iron. The propose venting was passing trough that area but it was not connected. I was planing of going pass the 3 inch cast iron then turn 90 degrees to go behind the low wall and conect on the oposite side where the 2 inch venting is. That's why I was asking about going below the highest fixture.