Whats the deal with plumbing vents?

[inetdog]

You are all missing the point.
The true reasons for the vents are actually to allow air to enter the plumbing to prevent a slug of water creating a vacuum and sucking the water out of the traps allowing sewer gas to enter the house

With a secondary purpose of preventing a high pressure event in the sewer line (either at the street or in the house plumbing) from forcing sewer gas back past the water in traps.
Flushing a toilet with a backup in the pipe below the toilet, for example, can cause a transient high pressure in the plumbing system above the toilet. We do not see this happening in typical construction because of the vent to atmosphere.

[Naptown]

You are all missing the point.
The true reasons for the vents are actually to allow air to enter the plumbing to prevent a slug of water creating a vacuum and sucking the water out of the traps allowing sewer gas to enter the house

[bridaus]

I don't think you understand the idea.

Apologize, my comments were getting general, not relative to your specific instance. Sorry about that!

[Andy D]

I can definitely (aside from code) see reasons for:

1. Vent exiting above roof and not in house (noxious gases should remain outside the home).
2. Vent being a certain diameter (for condensation and all kinds of plugging reasons including critters).
3. A certain reasonable height above the roof to avoid water/snow/any foreign debris from entering.
4. Workmanship such that cracks/gaps/some low amount of abuse would not cause gases to release within house.

I cringe when I see the missing panel on installations, and just think to myself how there are more elegant solutions.

I don't think you understand the idea.

We are not venting inside the house! We are attaching a 90 fitting to the vent pipe on the roof (sawing it down in height first), extending it horizontally to get out under the panel with a slight pitch, then another 90 to go up a foot or two. Nothing inside the house or attic is being touched!

I don't see any safety hazard here. I know it' s probably not to code but as a homeowner post inspection, I really don't care!

[Andy D]

A plumbing vent INSIDE the house can be less than 3", but there is a reason the code calls for 3" minimum plumbing vents through the roof. The reason is condensation in freezing weather. Pipes smaller than 3" can be choked off by an ice plug that forms when condensation in the pipe freezes.

--mapmaker

Code where? I live in Los Angeles in a 1990 built house. Most of my vents are 1.5in - some 2in. We don't get ice storms here.

[foo1bar]

code calls for 3" minimum plumbing vents through the roof.

In my area it doesn't.
It's possible that's because I currently live in an area that doesn't get freezing weather.
But I don't believe it's required in WI either, and they do get freezing weather there.

[bridaus]

I can definitely (aside from code) see reasons for:

1. Vent exiting above roof and not in house (noxious gases should remain outside the home).
2. Vent being a certain diameter (for condensation and all kinds of plugging reasons including critters).
3. A certain reasonable height above the roof to avoid water/snow/any foreign debris from entering.
4. Workmanship such that cracks/gaps/some low amount of abuse would not cause gases to release within house.

I cringe when I see the missing panel on installations, and just think to myself how there are more elegant solutions.

[mapmaker]

Not to be argumentative but I don't see anything here that is a legitimate safety issue, code aside.
<snip>
A 90 degree 1.5in water pvc fitting will clear my panels, I measured this weekend. An ABS fitting is about 3/4in too high.

A plumbing vent INSIDE the house can be less than 3", but there is a reason the code calls for 3" minimum plumbing vents through the roof. The reason is condensation in freezing weather. Pipes smaller than 3" can be choked off by an ice plug that forms when condensation in the pipe freezes.

--mapmaker

[foo1bar]

1. If the panel is sandwiched glass, how will any compounds/smells from the vent do anything to the panel?

2. Near as I can tell, the code for height above roof (in the Northeast at least) is for:

It's not sandwiched glass for most panels. From top to bottom it's glass, silicon wafers and wires, then a backsheet that's made of some sort of plastic.

I always thought the height was because the air flow is similar to a chimney. Ideally you want a chimney to be above the roof peak. If it isn't, on some days you can have a LOT of problems with air blowing down the chimney if the wind is coming from certain directions. The higher above the roof's slope you are, the less issues you have with the wind direction affecting you.
But that's just my understanding of the reasoning behind the code requirement.


I've had to deal with a contractor-installed joint where ABS glue was used on PVC pipe. At least I assume it was ABS glue - it was black, no primer, and didn't bond well with the PVC. Did it work fine for a few years - yes. Did it eventually leak and let rainwater in because it was a local low spot? Yes.
So I have a personal pet peeve about people using glues that aren't meant for the pipe they're gluing.

And if water can get out, you know that gasses can (and are) getting out. Sure the gasses are likely to *mostly* be going out the larger opening to free air. But some is going through the cracks in that joint.

[bridaus]

I have thought this myself:

1. If the panel is sandwiched glass, how will any compounds/smells from the vent do anything to the panel?
2. Near as I can tell, the code for height above roof (in the Northeast at least) is for: Rain water/Snow and ice blockage, which wouldn't happen under a panel (yes water running down roof, so you have to have some protrusion there, how much?)
3. Oh no, I have to lift a panel to put in a snake? Let's see, in twenty years and five houses, I've had to do that exactly.... carry the zero... plus zero.... zero times.

So why can't a panel go over a vent again if there is enough height to keep out rain water and full coverage from snow/ice?

[Andy D]

Not to be argumentative but I don't see anything here that is a legitimate safety issue, code aside.

1) Gas leaks? How much leakage is going to happen at the press fit joint under the panel when the end of the pipe is wide open four feet further? Think like an engineer! Pressure differential! And as one of you said, you can glue the joint, it's just not mechanically sound but would surely seal against gas escape.

2) Roof angle? I was thinking about running the vent extension horizontally. My rails are horizontal.

3) Rain entry? Well gravity still exists. Any rain is surely going to go along the extension and down the vertical pipe. A half inch slope over three feet should be more than enough.

4) Clean out snake? If necessary, lift the panel and flop it aside or even disconnect it temporarily. (requires a non glued joint though) -or- Just pay the $300 for the extra snake work. For an many times at that particular drain would ever clog, I'll take that risk.

5) A 90 degree 1.5in water pvc fitting will clear my panels, I measured this weekend. An ABS fitting is about 3/4in too high.

I am going to do this to fix the ugly patchwork by adding a panel on one of my slopes. Off permit of course! And yes the string can easily take on the extra panel electrically.

[sensij]

Plumbing roof vents are often used as a entry for a snake to clear drains, instead of tearing up the plumbing under a sink.

+1. I have cleared my kitchen drain twice this way, when the snake from the bottom wasn't getting it done.

As for re-routing the line parallel to the roof... if you don't mine a jog in the line, you can match any angle with a pair of 90's.

[Mike90250]

Plumbing roof vents are often used as a entry for a snake to clear drains, instead of tearing up the plumbing under a sink. Hide it under a panel, with 90's, and you can't use a snake, so the $90 drain cleaning charge jumps to $300 to take traps out and snake from under a sink.

[solarix]

Ya, plumbing vents. They can be a pain. Definitely can make an array look awful - all chopped up into a patchwork quilt. Can't really make enough room to snake them out underneath the array. Mounting rails generally get in the way (unless your rails go vertically up/down the roof - which makes them a pain to match up with the roof framing. Sometimes on particularly bad situations, we'll go to the trouble of rerouting the vents in the attic to get them out of the way which is nasty, hot attic work - but worth it aesthetically in my opinion.

[foo1bar]

Now we know that PVC cannot be bonded to ABS but who cares. It's just a vent and above the roof line so a press fit should be more than good enough. And the panel over it will help keep it from moving up.

1> PVC can be bonded to ABS. It's not a great bond, but I've seen it done. That said, I still wouldn't glue them together OR reroute a vent above the roof.
2> a 90 to go horizontal across the roof face wouldn't meet the slope requirements for rainwater coming in to drain down the vent.
And most roofs/vents, a 90 or 45 isn't going to match the roof pitch, so you can't get up-slope from the panels, which is really what you want to do.
3> your vent (which with a press fit is now guaranteed to be leaky) is where sewer gasses come up from the plumbing. It is very likely that there will be fumes that you don't want wafting onto your panels if you can avoid it (sulphur and acid compounds from things breaking down, chlorine bleach and other household cleaners that you use on your plumbing fixtures, and who knows what else)

The answer is to just do a 45 in the attic, run it 4' or whatever to get it up-slope from the panels, another 45 to go back vertical, and put in a new penetration through the roof.