What does your code book say?

 

Ultimately, code is god. But with advent of low flow toilets and only two bathrooms, I would stay 3" for main until it exits house, then go to 4". And 3" would be fine for main vent as well. But always, code first.

 

Sounds over sized.

Depending on the authority having jurisdiction. You should always consult with the local authority and make sure you know what codes to follow. I live in Washington state. As far as we are concerned up here, your main trunk line is over sized as well as the 3" stack for the laundry. I would suggest hiring a certified real plumber to engineer the system correctly. It will not hurt to have larger drains than needed. However, you will need to adjust the venting size to meet the cross section requirements. This will result in possible trap siphonage and could leed to methane gas leeking into the room. Either way hire a licensed plumber to do the job.

 

Many of the jurisdictions in this locale have one person, often part-time, who does permits and inspections. Qualifications? Nothing like what is needed in a large or even medium-sized metro area. Plumbing often is not inspected at all.

The state residential code is what is observed in all the towns, and it says that for my 18 dfu count (I had not counted the dishwasher before), a 3" building drain will suffice. Is sizing up to 4" a good idea?

The code also says, re venting, that "the minimum required diameter of individual vents, branch vents, circuit vents, vent stacks, and stack vents shall be at least one-half the required diameter of the drain served."

I have heard of some jurisdictions (not this one) that cover deep snow country, that the minimum size of the vent at the roof is 3".

The design of the house is such that all three fixtures in the upstairs bath drain down through a mainfloor wall that is not stacked atop with a second floor wall, so there is no 3" vent stack in any of the second floor bath walls. All venting snakes around through floor framing and up through walls, to get to the attic, where all will tie together into a stack that will penetrate up through the roof.

If that single vent is considered the vent for all below, and all below go into a 4" main building drain in the crawlspace, and the largest vent of any of the fixtures is a 2" (that would be both toilets), then one might think (if he or she was unschooled in the plumbing code like me) that a 2" top vent would do. I was thinking of making it a 3" a foot or two under the roof deck using an increaser fitting.

I don't care if you don't want to answer and instead tell me to hire a plumber. That's the plan, but there's no telling how good he will be. I've been involved in a few kitchen and bath remodels here, and have seen plenty of unvented or badly vented or plumbed work.

I'm just curious, is all. Hey, it's the weekend, there is no pro to call on the phone that can answer, and it is too slushy to ski today.

Edit: BTW, there is no certification for plumbers here and no licensing, either at the state or local level. A lot of plumbing gets done by a jack-of-all-trades guy on the contractor's payroll that learned to pipe from someone else, and that guy often does the wiring, too.

Edit2: In that first pic, the three drains at top L are for the main bath shower (2"), toilet (4") and lav (1-1/2"). The red below it is the 3" drain into which has gone everything from the upstairs bath. Adjacent it and wye-ing into the red 3" drain is a 2" from the laundry box. At the R is the 2" from the kitchen sink. The DW drains into the kitchen sink drain as is common.

 

3" main & vent should be fine.
If fall gets to be an issue you may need to bump up to 4" main.
Just don't skimp on the clean outs.:thumbsup:

 

A number of years ago Wisconsin went through a big code update. While not getting into detail I'll just say that we used 4" for all under slab plumbing except for a few things of course. When the code changed it virtually eliminated 4" inside the house unless the house has a lot of DFU's (drainage fixture units).

I'm old fashioned and I still use 4" where I can use 3" under the slab, I'm not sure why and I'm not sure it really matters I just do it. I don't charge anymore labor wise and material cost is hardly nothing.

I guess maybe it's because I've run a lot of sewer machines and it's nice to have the room.

On second thought...maybe I'm just stubborn and getting old and refuse to change.:laughing: That's possible.

Mike

 

Mike is the intent of the code ( using 4" under a slab)be wise in case of additional loads down the road? Just asking if that's the purpose.

 

No, it's based on a formula for probability of usage with the designed fixtures on the system. The old code has a special clause that said "regardless of DFU's no more than 2 toilets on 3"

I always ran 4" just because I felt it was wise, but it probably doesn't matter. I also pitch more than just the minimum 1/8" per foot. I can tell you from experience that 1/8" is BS on underfloor, it should be more. I pitch the hell out of my sewer pipe. When the sh## hits the city sewer main it's screaming fast baby.

Mike

 

NYC Code requires at least one 4" building house drain and one 4" vent stack per dwelling.

Keith

 

Usually for what you have, a 3" vent with everything tied in the attic except a revent (usually for the washing machine) of 2". That goes through the roof also. To further prevent freezing, switching this 2" to a 3" about a foot below the exit point should suffice.

I wouldn't see any need for a 4" line unless you have a long horizontal run. Even then, probably not necessary.

 

For the vent you would never need 4" in a house

 

You are correct. Too much pitch is not good. 1/8 to ¾" is okay but you don't want more than that for the reason you mentioned - liquid will outflow a solid.
and don't give me no crap about a vertical drop, griz. no pun intended.

 

I've never heard of too much pitch being a problem. Keep in mind that on a house I'm responsible for the drain up to the point of connection, usually dead center under the foundation wall. These days I don't do any outside work anymore.

With that said, most plumbers who do exterior laterals give it extra pitch.

One of the problems with 1/8" per foot of pitch often times happens years later after the ground has settled. 1/8" is not much pitch so it's easy to develop flat spots in the lateral. Some of this is natural but most of it is caused from the plumber doing a poor job of bedding the pipe in the correct material and packing it to make sure it's solid. This is also one of the benefits of cast iron.

Over the years I have seen a lot of sewer laterals with a camera and the flat spots (no pitch) show up like a sore thumb. You can't hide sins from the camera.

So I have learned that it's a good idea to give it extra pitch, bed the pipe well by spending extra time packing the trench solid, and keep any soil debris out of the way.

I pitch my sewer between a 1/8 and a 1/4. That may net seem like much but it's a lot for a 4" pipe. Remember, it's a liquid....the solids get busted up pretty well by the time it hits the sewer.

Anyway, I highly doubt too much pitch is a problem. I mean, man, in all these years I have yet to clean a sewer because it had too much pitch. I say the more the better, but keep in mind that after 1/4" on 3 or 4" pipe it becomes unrealistic because the ditch gets pretty deep.:laughing:

You figure that most ranch homes are in the neighborhood of 50 feet so if a stack is at one end and the lateral exits about half way that's 25 feet so the drop is 6 1/4".

Now figure you should be at least 4" under the bottom of the concrete so you don't have cracking problems. Then figure you should have a minimum of a 2" bed under the pipe so you don't get the flats spots I talked about and you end up with a trench exiting that's pretty dam deep.

You can see how unrealistic going past a 1/4" is but like I said, if you hit 1/4" on 4" pipe that motha is screaming.

Mike

 

Okay; the way you said it I thought you were talking about something ridiculous. I usually try for about 1/4" myself. :thumbsup:

 

For the vent you would never need 4" in a house

Maybe I wasn't specific. I was referring to the drain for 4".

 

Arguments about code will always be present. Every city, state and government branch have there own standards and codes. I understand the fact you are in a remote area without a lot of real professionals around. I would recommend finding a licensed plumber in the nearest populated city. It sounds like you are high up in the foot hills were there is a lot of snow fall. If this is the case then a min. 3" vent is going to be required to keep the vent from being filled with snow. Regardless of your VTR (vent through roof), you only need to bump up to 4" when you have 4 toilets in the house. This means after the third toilet is tied into the trunk you must enlarge to 4" to pick up a 4th toilet. I know there will be disagreements on this. However, I am a 15 year journeyman out of Washington state. We have our codes as does every other county and city. Everything is subject to argument. I know what works for us up north.

Our code states you can run:
Drainage: 3" for max of 48 DFU vertical, 35 DFU horizontal / 4" for max of 256 DFU vertical, 216 DFU horizontal.
Venting: 2" for max of 24 DFU / 3" for max of 84 DFU

When sizing your vent to meet the cross sectional of the building sewer you use this equation as follows.

The square of the diameter of a circle multiplied by .7854 equals the are of the circle.
The cross section of the combined vents must be grater then the cross section of the buildings sewer line.
To insure that air circulates through all parts of the system start at the properly sized out going building drain. Go upstream on the drain line to the first VTR. Take this cross section and add to most remote vent. If the drain size is not the same or grater than the out going sewer, you must up size it. Continue up stream and repeat the process.

To find the cross sectional of any pipe size the equation is:

(pipe size X pipe size X .7854)

Example of 3" pipe's cross sectional:

Building drain size is 3"
(3" X 3" X .7854) = 7.0686"

This means you must find the cross section of each vent, add them together, if that number is less then the cross section of the buildings drain, then you must up size the most remote vent to meet the venting requirements.

If you need more help on this concept let me know. This is the correct way to size a systems venting to the main building drain.

 

As far as grade is concerned. stick with 1/4 per foot. any more then that will leave solid deposits behind. grease and fat will solidify on the top layer of the fluid as it travels down stream. If its velocity is to high the solidified grease and fats will begin to build up as it is pulled across the pipe on its decent. The grade is not so much saying it will out run the toilet paper or fecal matter. It is more about the deposits that stick to the walls of the pipe. the only time you can use a 1/8 per foot grade is when you have at least a 4" sized pipe. We are not allowed to run sewage through it only storm drainage at that grade. Never run a pipe at less than 2% or 1/4" per foot for sewage. If you run it less it may work and in some places be legal. However, you will only be asking for a problems down the road.

 

Wisconsin ha always been 1/8 and in some cases 1/16.

I don't buy into too much pitch though, that means 22 deg would cause problems. Lots of exterior sewers are screaming fast and pitched heavy and never have problems.

Most problems are because of poor pitch, poor bedding, and poor materials for the bedding.

Mike

 

I read an engineering article a few years ago that debunked the "too much pitch" theory. They did a study and found that more pitch equals higher flow, period. You're far more likely to have problems with too little pitch.

Keith

 

Yeah, I tend to agree. When I shove the camera in a pipe and you see standing water the owner usually wishes the pipe had more pitch.:laughing:

Besides, and like I said earlier, we are pretty limited to how deep we want the trench inside a HO's basement. I don't mind digging but once I hand dig past 12" or so I get pretty tired these days.:laughing:

Mike

 

I have always been an advocate for 4". Though now our local code is based on a total DFU count, however 4" pipe at 1/8" per foot will carry 180 DFU's. And 4" pipe at1/4" per foot will carry 216 DFU's. Finally 4" pipe at1/2" per foot will carry 250 DFU's so obviously there is a direct correlation in pipe size to pitch.



Thou I am sure 3" pipe will satisfy your needs I am still advocating 4" is better long term.
Always check your local area.