DWV Design Questions

[icanreachit]

Hey everyone,

I may have skipped the formal introduction but I seem to lurk a bit and post where I can be helpful so I was hoping to get some feedback. I've got an 1100 sf design that I am working with currently and am just waiting on my survey. I'm currently posted abroad so I'm unable to work on anything physically at the moment - as a result, I'm trying to tackle the planning down to every last screw.

You can roughly see in the picture below the plumbing. I've tried to boil it down as much as possible but I've only ever plumbed a bathroom before. A whole house (let alone a two story) is a bit complicated. Seeing as, as an engineer, I tend to over-complicate when I should be KISS, not the band, any help would be greatly appreciated!



https://www.flickr.com/photos/147502503@N06/34925863574/in/dateposted-public/

Biggest questions at the moment:
0.5) Can anyone see the photo?
1) Can I bend the soil stack like this? None of my lower walls align with my upper walls in a way that would be conducive.
2) Can I wet vent the lower WC? I'll try to find the tables on this.

[ChugiakTinkerer]

Sorry, I can't help on the plumbing questions.  There's a reason I'm building a dry cabin! 

I do want to confirm that I can see your posted pic of the plumbing, and I also want to offer a belated welcome to the fourm.

[icanreachit]

Thanks Tinkerer! I wish that that were an option for this one but as I've got time, I've purchased a few books and am trying to make it a learning process as well.

[Dave Sparks]

Can you do this bend to code?  I don't know,  but you can do just about anything if there is a clean out and access.
I doubt it on the second question. You will get better answers, electrons are my specialty and definitely not plumbing. 
We did have a great plumber when we built and I had him use only one 3" penetration in the roof for venting the whole house.
I am guessing that in your drawing, the 3 inch bend on the second floor, in my home it goes straight up to the roof vent. If the second floor 3" drain were plugged the ground floor would still vent.

[NathanS]

I'm not a plumber either, I did plumb my house and spent a lot of time reading books and the code. The code is pretty dang confusing, even my brother in law plumber confesses that.

The best plumbing book I read was the yellow one by rex cauldwell, i think just called PLumbing, for pros by pros. He summed it up really well somewhere in that book - if you oversize all your pipes even when everything is turned on and running, they will never completely fill with water, thus you'll always have airflow aka venting. PVC pipe is really cheap.

That first floor toilet doesn't look right to me, it has to pass through the soil stack for the wet vent. My understanding is that you generally want your wet vent to be on it's own branch off the main line. The other rule in the code is that you can horizontal wet vent 1 foot for every quarter inch of pipe diameter - so a 2" pipe can have an 8 foot wet vent. To sleep well at night as a DIYer it might be better to just dry vent everything you're not sure about, and oversize all the pipe.

Another controversial topic are the air admittance valves, I don't think there's a thing wrong with them, it can save some nasty vent line runs - looking at the sink off on its own.

Just as another thought. if that the main soil stack was not upstream from the toilet, and you ran 3", even 2" would probably be fine, to the sink on it's own and then stuck an AAV there, I would not at all be worried about the toilet vent downstairs.

If you are going to have a code inspector, show him your diagram and let him tell you if he's ok with it. Also in addition to the plumbing section in the IRC there is an appendix with a ton of diagrams with venting examples - one may almost exactly match your plans.

Lastly, my code guy said my upstairs toilet was too far from the wet vent - saying that all vents must be 5' from an appliance. I said the code says 1 foot per 1/4 inch of pipe diameter is what the code says, he said well it depends on which code you read. He dropped it and said I should be fine. A different code guy told me that toilets are self venting, whatever the hell that means. I asked my brother in law (real plumber) about both, he said neither of them were right.

Anyway if it's not confusing you haven't read enough, in my opinion oversize all the pipes and dry vent unless you can really visualize that plenty of air will always be available to the fixtures. You will save thousands doing it yourself, and extra $50 on larger pipe is nothing.

[MushCreek]

I can only sympathize- plumbing is the WORST! I have a small library of plumbing books, often with conflicting rules. I tried to hire a plumber as a consultant; no go. Searching all over the internet, solid advice was hard to come by. Various DIY sites said, "Hire a plumber." I wound up venting the heck out of everything, it passed inspection, and it works well, but I still don't feel confident in my knowledge. By comparison, other building codes, like electrical is very cut-n-dried. As I learned about DWV, I discovered that my under-slab plumbing (done by a professional) is not to code! It works, so I don't care.

[flyingvan]

The big box stores offer simplified flip charts that show the basics...I'd have to compare your picture to my chart to find everything, but there are some problems with your design.

1) Your upstairs bathroom, if all tied to the same drain, should branch in to the main past everything else.  A clog downstairs would result in an awful overflow mess.

2) Your downstairs toilet needs its own vent.  You really need a lot of free air to follow the water after a flush, and I don't see any.  You can get away with ONE AAV in your system, but check local code---while your at it, ask if---

3) Wet venting is permitted.

4) DO your future self a favor and provide cleanouts.

5) The cross section area of your through roof vents must be equal to or greater than the cross section area of your main drainpipe.

6) Your kitchen sink needs a vent and I'm concerned about that long run. 

[icanreachit]

Thank you everyone for the great feedback! I've tried to do more research by looking at how people add bathrooms to their basements. From what I've seen, this tends to be after the soil stack has been turned horizontal so I think that my bend is more or less analogous.


https://www.flickr.com/photos/147502503@N06/35786096746/in/dateposted-public/

At this point I am fairly comfortable with what's happening upstairs, it's jut downstairs that's off.
Changes:
I've dry-vented the lower toilet
I tied all of the venting together downstairs to minimize how many things go through the roof (still need to tie in the lower shower/sink)
I moved the washer drain upstream of the downstairs toilet. I figured that with the huge rush of water, it would help to flush anything that wants to linger.

Flyingvan - I stopped short of your first suggestion because I'm trying to figure out where to tie them together. I would rather only one line perforate the foundation wall, but that may help for cleanouts.

[icanreachit]

Alright, the more I thought about it, the better flyingvan's idea was to separate the floors. Not only does this simply flow calculations and venting, but it allows me to test the two independently.

One other change. I bumped up the size of the pipe that serves the sink. This way, the air entrance valve is only for contingency as the distance between the sink and the first vertical vent is only 10 feet. With a 4" line, it should be able to go 16' and still act as a vent for that branch.

I also thought it would be good to include a rendering of the project to give everyone an idea of the project. Context.


https://www.flickr.com/photos/147502503@N06/35118106313/in/album-72157682791319222/



href="https://www.flickr.com/photos/147502503@N06/35795428031/in/album-72157682791319222/

[Dave Sparks]

Very nice!  So, no plan check, no AHJ involved? Good to go!

[icanreachit]

Thanks Dave!

We have a homeowner's exemption that allows us to do regular tradeskills in my area. Only rules are: no gas plumbing and no HVAC work. I've done both and am a Mechanical engineer by trade so I feel comfortable with them, but I understand the rules and why they have them.

Only problem with my city is that they don't do consults on things like this. They just show up for the inspection and give you a thumbs up or down. Thus my pre-planning.

[dablack]

So, I'm crazy late to the party but had to throw in my 2 cents as well. 

I'm a mechanical engineer but built in an area where there is no inspections (gotta love rural Texas).  One thing I did to simplify plumbing was to place the two upstairs bathrooms back to back and they are also above the kitchen.  I also used 2' tall floor trusses for the 2nd floor.  I like them better than the I-beams because they are open and easy to run AC, wiring, and plumbing. 

Have a good one,
Austin

[JRR]

Having almost nothing to do with subject at hand .... let me remind that "unions" exist for PVC piping.  They are a bit pricey for 4" and 6" PVC pieces, but with a bit of planning they can make sections of pipe easy to disassemble without having to grab the hacksaw.  Of course, one can always use rubber couplings, but screw-type unions make a nicer/stronger job in my book.

...for threaded and non-threaded schedule 40 (and others): https://www.mcmaster.com/#pvc-pipe-unions/=19cspx9

[jdindino]

Having almost nothing to do with subject at hand .... let me remind that "unions" exist for PVC piping.  They are a bit pricey for 4" and 6" PVC pieces, but with a bit of planning they can make sections of pipe easy to disassemble without having to grab the hacksaw.  Of course, one can always use rubber couplings, but screw-type unions make a nicer/stronger job in my book.

...for threaded and non-threaded schedule 40 (and others): https://www.mcmaster.com/#pvc-pipe-unions/=19cspx9

Good information, I didn't know that this type of fitting existed. It certainly would make repair easier down the road.

[JRR]

Good information, I didn't know that this type of fitting existed. It certainly would make repair easier down the road.

Yes, indeed.  I wish more of the plumbing publications for DIY's would suggest the prudent use of unions.  Unless specified, why would a contractor ever use them?  Just additional cost with no benefit (for the contractor!).

Some big-box stores offer them, but usually only up to 2" or so.

[UK4X4]

Joints.......basically failure points  the more there are the more the possible leaks can occur in the future.

If you add in joints for future repairs etc make sure they are accessible and have worth after everything else has been installed.

Wiring too, I never join wires in walls, if I have too in a remodel then they are installed behind an access hatch.

Wires don't often fail but joints do !

Happy plumbing !

PS when doing vents you do not have to bring them through the roof....it is acceptable under the eaves.....but there is a civit about distance from windows that might prohibit this.

[Dave Sparks]

Vents are hard to do under the eaves because as you said the window and distance requirements.
With a really good plumber, you can request that he condense all the different vents in a house down to one 3" hole in the roof.
There has to be enough pitch in the roof to do this (needs lots of attic space/height) You would not do this for a mansion