[coolguynick]

Is every sink supposed to have a vent underneath? I have a vent underneath every bathroom sink in my house…except for a bathroom with two sinks in my master bathroom.

Here’s a picture of both sinks.

Here’s a picture of both sinks during construction.

This is the right sink. Notice it has some of vent opening at the top.

The left sink doesn’t have any vent.

Is that normal? The only reason I ask is I notice every bathroom sink (most are only one sink) and kitchen sink has a vent underneath. Not sure if the one vent works for both sinks in the master bathroom, but wanted to ask and confirm.

EDIT - I actually noticed the utility sink in the laundry room doesn’t have one either.

To confirm, I have 6 sinks in my house. They all have the vent except for the dual sink in the master bathroom and the utility sink in the laundry room.

 

[TheEplumber]

Modern codes say every trap shall be vented and there are multiple accepted ways to vent a trap. The method you have is called Air Admittance Valves (AAV) I work with a modified version of the UPC and AAV's are very restricted in use.
IPC seems to be much more lenient with them.
The sinks that don't have AAV's probably have vent pipes in the wall, which eventually exit the roof. This helps balance air pressure in the building drain.
BTW, your toilets, showers and tubs are vented as well. They probably share the vents that are concealed. AKA- 'wet venting'

 

[Half-fast eddie]

I can’t believe you have 4 aav vents. Normally they are used in unusual situations where yo7 can’t do a normal vent.

 

[coolguynick]

Modern codes say every trap shall be vented and there are multiple accepted ways to vent a trap. The method you have is called Air Admittance Valves (AAV) I work with a modified version of the UPC and AAV's are very restricted in use.
IPC seems to be much more lenient with them.
The sinks that don't have AAV's probably have vent pipes in the wall, which eventually exit the roof. This helps balance air pressure in the building drain.
BTW, your toilets, showers and tubs are vented as well. They probably share the vents that are concealed. AKA- 'wet venting'

I can’t believe you have 4 aav vents. Normally they are used in unusual situations where yo7 can’t do a normal vent.

Ok, after doing some research, I looked through some other construction pictures.

The utility sink (that doesn’t have a vent underneath) is right next to (and probably) connected to the main vent in the roof.

The sink is located just to the right, so I have to assume it’s connected.

The two sinks in the master bathroom have me somewhat concerned because the one to the right has an AAV vent…but the left doesn’t. If the right has a vent, I assume it’s for a reason and wonder why the left doesn’t?

Are there’s any risks or concerns for not having the AAV? It’s under warranty, so is it difficult for a plumber to add to the sinks that are missing it?

 

[Matt1963]

Funny your left sink doesn't have one. If it the two sinks we saw in the first construction picture than yes, it's missing it vent. Does it drain slow?

Not sure why on a new build they didn't use normal vents. AAV's are more for retrofits or islands.

 

[icerabbit]

Dual sink bases often use one drain line, or share one branch to a vent line. Without a vent line to the roof on that side of the house, both sinks actually benefit from the one AAV, to allow air into the waste line.

Otherwise when you see a fixture without one, it must be near a branch or main vent.

Really makes for a clean and efficient setup, versus running vent pipes all over.

 

[coolguynick]

Funny your left sink doesn't have one. If it the two sinks we saw in the first construction picture than yes, it's missing it vent. Does it drain slow?

Not sure why on a new build they didn't use normal vents. AAV's are more for retrofits or islands.

Dual sink bases often use one drain line, or share one branch to a vent line. Without a vent line to the roof on that side of the house, both sinks actually benefit from the one AAV, to allow air into the waste line.

Otherwise when you see a fixture without one, it must be near a branch or main vent.

Really makes for a clean and efficient setup, versus running vent pipes all over.

My old house must have been like this because there was only one roof vent as well (for washer vent).

The yellow it the main drainage pipe, and both red lines are the sinks (connected to the main drainage pipe for that area).

1. Is only one vent on the right sink needed because they’re both connected to that yellow pipe?
2. Does the little vent underneath the sink let in sewage gases since it’s before the P Trap? It’s an Oatey Sure Vent.

 

[TheEplumber]

My old house must have been like this because there was only one roof vent as well (for washer vent).

The yellow it the main drainage pipe, and both red lines are the sinks (connected to the main drainage pipe for that area).

View attachment 729012

1. Is only one vent on the right sink needed because they’re both connected to that yellow pipe?
2. Does the little vent underneath the sink let in sewage gases since it’s before the P Trap? It’s an Oatey Sure Vent.

To answer #1 you need to review your local plumbing code and Oatey install manual. I work with UPC, which is used world wide and allows AAV's only in certain applications. Your example is not one of them. UPC is very limited on their use, where IPC seems to allow them in almost any situation

The AAV is a one direction valve that does not allow gas back into the room unless it has failed.
IMO, I could have vented your lavs with one shared vent out the roof for about the same cost time- maybe cheaper and we wouldn't be having this conversation

 

[chandler48]

I could have vented your lavs with one shared vent out the roof

Probably for much less. Figure 3 or 4 lengths of pipe and fittings, versus $20 per AAV, and they still aren't fool proof.

 

[rhmalsch]

Do you have zoning/building codes where you built? Was a building permit issued? Were you allowed occupancy? If so and you don't notice any problems, don't worry about it. The science behind it is drain pipes are designed to flow at a rate where they are no more than half full so that air in the top half of the pipe will prevent a vacuum from pulling the water seal from the trap. If that happens you will definitely notice the odor of sewer gas. The size of the pipe and distance from the trap are deciding factors. From the pics it looks like the one device should vent both drains. I agree with the plumber. I would much rather see pipe for venting.

 

[icerabbit]

But, getting the extra vent pipes in, means waiting for completion of the walls and roof; then routing vent pipes. Both sinks could have shared the same drain, imo (unless code no longer allows it), but I don't see how venting with n feet of pipe up the wall, over in the attic, then through the roof with a boot + labor time, be cheaper than a local AAV installed in the cabinet when the sink + lines go in.

I would rather have less / no roof penetrations.

Anyhow. If it is all approved, you live in it, don't stress it. Should the AAV ever fail, you can unscrew it and screw in a new one.

 

[TheEplumber]

Probably for much less. Figure 3 or 4 lengths of pipe and fittings, versus $20 per AAV, and they still aren't fool proof.

I quickly ran cost through Lowes- piping vent through roof would save 5.00. and I added a cleanout under the sink so a cable could navigate the fixture cross
Oh, I forgot to credit the santee and 90 in the cabinet.... maybe we're closer to 10 bucks

 

[Matt1963]

I quickly ran cost through Lowes- piping vent through roof would save 5.00. and I added a cleanout under the sink so a cable could navigate the fixture cross
Oh, I forgot to credit the santee and 90 in the cabinet.... maybe we're closer to 10 bucks

I don't see how one AAV on the right side drain line can properly vent the left side drain. Do you?

 

[TheEplumber]

I don't see how one AAV on the right side drain line can properly vent the left side drain. Do you?

View attachment 729039

No I don't. Vents are to be above the weir of the trap as on the other lav. In this case the drain goes vertical to the floor without a vent (S trap)
And all branches of wet vents are to be flat- such as a floor drain, toilet, shower, tub (traps at floor level
But hey, I don't plumb the code the OP uses
It is possible a vent is in the wall and goes across the ceiling to another vertical vent after the the ground rough picture was taken (field change)

 

[coolguynick]

I don't see how one AAV on the right side drain line can properly vent the left side drain. Do you?

View attachment 729039

No I don't. Vents are to be above the weir of the trap as on the other lav. In this case the drain goes vertical to the floor without a vent (S trap)
And all branches of wet vents are to be flat- such as a floor drain, toilet, shower, tub (traps at floor level
But hey, I don't plumb the code the OP uses
It is possible a vent is in the wall and goes across the ceiling to another vertical vent after the the ground rough picture was taken (field change)

There’s definitely nothing in the wall (or ceiling) for this.

I actually reached out to builder and they said I only needed one per bathroom.

What is the risk of not having a vent in the left sink? Everything drains properly and quickly

 

[Matt1963]

Sink not draining well, trap being siphoned out causing smells of sewer gases in your bathroom.

Maybe it was changed behind your walls....

Should have been more like this but with a AAV installed.