Drain/vent in exterior wall options

wildbilly

I adding a sink against a exterior wall. I am concerned about things freezing. I am concerned that the for sure vent/code application to run the drain after the s/p trap into the exterior wall to a T (up going to vent and down to drain which will run back inside under the floor) will freeze up here in the north where this morning it was below zero. Granted water will not stay in the drain but could it build up ice or such and be a problem??

I like the alternative method of running the drain after the s/p trap through the floor into a T (horizontal, downslope going to the drain, upslope going to vent) and the vent being routed into the cold then with a 90 degree turn up thru the roof. I don't think this meets code and I'm not sure that it will vent properly. Anybody know for sure?

On another note about venting. Once I have a vent into the attic, why shouldn't one not turn a vent horizontal (slight slope though) at the highest possible point and run it over to the stack or other vent. That is versus making another whole in the roof and going straight up of close to it? Would a short horizontal turn and then up be allowed on a vent in the attic?

Thanks for any help I hope you can understand my descriptions. I can clarify if the need be.

ponch37300

They make a mechanical vent(AAV) that goes right after your trap and then you don't need the vent to the attic and can run your drain straight down. This is one option, I'm sure others will chime in.

wildbilly

Unfortunately in Minnesota air admittance valves are not allowed per the plumbing code.

I thought about using one as eventually they probably will be allowed.

jogr

I'm pretty sure an S trap to the floor is a no-no since it can siphon itself. Instead use the AAV or if you have the sink on a cabinet you can set up the normal p trap to Sanitary T but place the sanitary T in the cabinet instead of the wall. Then you can add a 90 to the top of the T to bring the vent back into the exterior wall. That way your drain portion is within the heated space but the vent is in the exterior wall.

Once your vent is above the fixture level such as in your attic you can run it horizontally over to another vent so you only put one hole through the roof. The make sure the vent has a slight slope to drain so it doesn't funstion as a trap for condensation.

wildbilly

Jogr, Thanks!

As I said I can't legally use a AAV. Has anyone used one for a washing machine before?

Your idea makes sense and should meet code. I am in a cabinet so I will bring up the vent as high as I can (which will be above the sink drain) before it exists the wall. The drain will go straight down through the floor. Thus the only part exposed to the cold/exterior is the upper part of the vent. It will be a tight fit in the cabinet between the sink and wall but doable.

jogr

It doesn't have to be squeezed between the sink and the wall. You could offset it slightly to the right or left where there's more room.

jogr

Wildbilly,

A vague memory just flashed into my mind that horizontal runs of vent have to be above the waterline of the fixture. So maybe the short horizontal part of the vent from the top of the T in the cabinet into the exterior wall wouldn't be according to code because it is below the top of the sink bowl.??? I don't see how it will cause a problem but I don't want to be telling you to do something against code. Hopefully a plumber will chime in here and set us straight about whether this is ok..

wildbilly

Hmmmm, not sure what the vertical height of the vent has to be above. I hope someone helps.

I also seen a few other posts about the vent can only be so far away from the drain depending on the diameter of the pipe thus I wonder if I can run that horizontal line in the attic to another vent cause it would be too far away. I see in books were they run horizontal on a circuit vent so maybe it's just the distance to the 1st vertical section(that goes above the something waterline which is the question left over and noted above).

ironrange

The vent has to be a minimum of 6" above the flood rim of the sink before you can go horizontal as per Minnesota code. Nothing in the code book about running it outside though IMO it's not a good idea because of the cold up here.

wildbilly

Thanks IronRange.

I found this which leads me to believe I could run the vent vertical up as high as I can up inside the base cabinet and then run it through the wall at 45+ degrees into the attic space and try to achieve 6 inches above the sink rim which I think is barely possible in this case. That should meet code shouldn't it? That way only the vent is outside in the cold; what's your gut feel on that?

https://www.revisor.leg.state.mn.us/rules/?id=4715.2540
4715.2540 VENT GRADES AND CONNECTIONS.

Subpart 1. Vent grade.

All vent and branch vent pipes shall be so graded and connected as to drain back to a soil or waste pipe by gravity.

Subp. 2. Vertical rise.

Where vent pipes connect to a horizontal soil or waste pipe, the vent shall be taken off above the center line of the pipe. The vent pipe shall rise vertically, or at an angle not more than 45 degrees from the vertical, to a point at least six inches above flood-level rim of the fixture it is venting, before offsetting horizontally or before connecting to the branch vent.

Subp. 3. Height above fixtures.

A connection between a vent pipe and a vent stack or stack-vent shall be made at least six inches above the flood-level rim of the highest fixture served by the vent. Horizontal vent pipes forming branch vents, relief vents, or loop vents shall be at least six inches above the flood-level rim of the highest fixture served.

ironrange

Yes as long as it is 6" above the flood rim. Barely doesn't work, it has to be 6" to be code. IF it's not being inspected and it's 5-3/4" I'm sure it would work but it's still not to code.

wildbilly

I was looking at the back of a AAV package in the store and noticed that they put the AAV only 6 inches above the P/S trap below a sink as the diagram showed.

How come AAV's don't have to be 6" above the flood/water line?

JDC

There is no reason at all that you cannot run a drain and vent in an exterior wall. It is done all the time and if the piping is run correctly there isnt any water in the pipe to freeze. I live in Cincinnati where things get well below freezing and DWV is put in exterior walls all the time. I've never had one freeze up inside the wall. All that I've seen is vents on the roof getting "snowconed" from time to time.

As far as running your vent in the attic, again there is no reason you cannot run it horizontal at any point after the vent rises at least 6" above the flood level rim of the highest fixture served. As such, if you wait til its in the attic to turn it horizontal you're WAY okay. You can then run it over to the existing vent through the roof and tie it in.