I am an owner builder who is studying the codes, taking the local owner builder plumbing and electrical tests and am faced with a plumbing question that I have not yet been able to get a satisfactory answer to.
I am plumbing the DWV system with PVC. We are on the plumbing secion of the IRC. All PVC DWV fittings appear to be made with very precise dimensions (angles) and tightness. If I set the water closet flange even with the finished floor (horizontal) how do I get the main or branch drain to slope downward at 1/4″ per foot. By using a 1/8 bend and the normal Y, I can offset the toilet from the drain slightly, get tight, fully-inserted fitting connections and the 1/4″ slope per foot. Is this they way the master plumbers do it or are their other methods? For me, leaving the joint a little loose and hoping the glue will hold is not an option.
Replies
Once you get glue in the joint, you'll find that the pipe is quite flexible in the fitting - 1/4"/ft is no problem - even more is fine. Adding in an ell for 1/2 degree bend just adds expense and a place for a leak.
Forrest
FORREST:Thanks for the tip. I've found 2" PVC schedule 40 to be pretty tight even with glue. Guess I'll have to glue up a couple of 3" fittings and see if they are as easily manipulated as you say.Our area uses the foam core Schedule 40 for the 3" drains and it is pretty soft compared to the solid core Schedule 40 and to the fittings. We can't use a sanitary T on its back for a water closet so we use the Y and an 1/8 bend which allows me to tilt the assembly to any slope I need.
It will work fine.
Put the PVC cement on both the fitting and the pipe and make the connection. Twist the pipe 1/4 turn when it bottoms out. Cement on both pieces gives some extra time before the stuff sets up.
The PVC cement softens the pipe because it fuses the two pieces together. The assembly will give for your slope easily.
Try it on some scrap. You will see.
Speaking of plumbing slopes....
I was just reading through some specs on a house and the architect specified the drain lines to be 1/8" per foot. That shocked me. I din't think anything but 1/4" per foot was allowed.
Any plumbers want to comment?
blue
Too much slope and the water leaves the waste behind.
I'm not a plumber though.
There was an article in the last few years in, perhaps, the Journal of Light Construction by a mechanical engineer who designs piping systems. He said the belief that too much of a slope will separate the solids from liquids is a myth. He rested not only on his own professional knowledge but also pointed out that no code specifies a maximum slope. That was the first time I'd heard the matter discussed by anyone other than someone repeating the maxim.
WayneL5,
In the army I learned quickly that Sh## rolls down hill.. But I believe 3" and over is 1/8 " per foot and 1/4 " per foot under that. But I'm not a plumber, so let's wait and see what the answer is. I may be wrong myself..
Northeastvt
Up here, 4" and over MINIMUM slope is 1/8 per foot.
3" and under, MINIMUM slope is 1/4 per foot.
Max drop for a trap arm is less than the diameter of the pipe.
I wonder if, with the low volume of flush water from modern toilets, a shallower slope keeps the water from running away from the load.
That said, I think 1/8"/ft. would be hard to do accurately without having flat spots.
Forrest
1/4" is the way I remember the code, too. Is the 1/8" for everything? I could see it working and making life easier if there are little or no solids to carry, for a laundry room, shower, tub, etc. But downstream of a toilet or a kitchen sink with disposal it sounds risky.
-- J.S.
I don't feel like pulling out my code book right now so lets see if I can get this right from pure memory.
3" & smaller 1/4" per foot minimum
4" & larger 1/8" per foot minimum
Now having said that if you 1/8" per foot a couple of things must happen first.
1--- You need inspectors permission first
2--- there has to be a reason for running 1/8" per foot------ usually the only one allowed by the inspectors is a physical obstruction or exsisting connection point won't allow for 1/4" per foot
3--- You can only load up 75% of maximum fixture units when usuing 1/8" per foot that would be allowed at 1/4" per foot.Do you look to the government for an entitlement, or to GOD for empowerment. BDW
to be 1/8" per foot. That shocked me. I din't think anything but 1/4" per foot was allowed.
Back just after the dinosaurs, when I was in school, they taught that DWV had to be not less than 1/8, nor more than 1/4"per foot for slope. Most other 'architectural' slopes are 1/4" per foot, so, that value kind of gets used generally.
Some of that, too, comes from back in the day when we built a lot more buildings of block and fired tile--12" in 8' "courses" a bit better when you are using block and tile.Occupational hazard of my occupation not being around (sorry Bubba)
I have several sections in my house that are 1 ft per ft, and a whole lot more that are infinity per foot.
Right, you're allowed to use anything within 45 degrees of vertical, or 1/4" per foot. The 1/4" per foot slope keeps the solids moving along with the liquids. At 45 degrees and steeper, gravity does a good enough job on all of it.
-- J.S.
We were meticulous with our lines 1/4 in/ft, and when the septic inspector arrived, he didn't care, "since PVC is so slippery as long as it is down hill you're fine"
We'll stay with meticulous, but any merit to the pvc line?