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Old 12-29-2012, 11:02 PM   #1
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1 foot per 8 feet drop on final leg


I'm installing a longer run of 4" abs for a new bathroom. All along I used the pipe straps and level to make sure the drop was 1 inch per 8 feet. As I approach the pipe that I will connect to I notice that it is 1 foot lower. A guy I am forced to work with claims that the final 8 foot connection can be a much more steep drop than the usual. It would come out to 1 foot per 8 feet. I am lobbying for maintaining the 1 inch per 8 feet slope all the way to the end then installing a 90 degree drop. Who is correct? Is it ok to have a steeper drop for the final connection? Or should the slope be maintained till the end then a steep one time 90 degree drop? What are the implications of doing it one way or the other?

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Old 12-29-2012, 11:21 PM   #2
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1 foot per 8 feet drop on final leg


Drop in to it do not increase the pitch.

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Old 12-29-2012, 11:42 PM   #3
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1 foot per 8 feet drop on final leg


use a 45 or a 90 to make the drop
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Old 12-30-2012, 12:41 AM   #4
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1 foot per 8 feet drop on final leg


If you have too much slope the solids will separate from the liquids. Use 45 offsets as mentioned or you could increase grade to a maximum 1/4" per foot.
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Old 12-30-2012, 02:49 PM   #5
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1 foot per 8 feet drop on final leg


1 inch per 8 feet is wrong.

Your whole line should be 1 inch per 4 feet.


Unless you're using the metric system.
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Old 12-30-2012, 04:21 PM   #6
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1 foot per 8 feet drop on final leg


Municipality dependant but the NPC in Canada states that:
A) a 4" building drain can slope at a MINIMUM of 1"/8' or 1:100
B) the code also states while minimum grade is acceptable, increased slope is recommended whenever possible.

If I was running this drainage I would aim to increase the slope over the entire run, or use 2 45's near the end. If you jump the slope up drastically for a mere 8' feet of pipe you will end up with very poor connections at the hubs when you glue them together.

Even if you use minimum grade, the liquid will seperate from the solids and it will take a few flushes for the initial solid to leave your DWV system. Its a sort of poop croquet you got going on in there.
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Old 12-30-2012, 05:08 PM   #7
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1 foot per 8 feet drop on final leg


I Thought Optimum was 1/4 inch per foot? Why are you Dropping at 1/8" Per foot?
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Old 12-30-2012, 05:10 PM   #8
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1 foot per 8 feet drop on final leg


Quote:
Originally Posted by Alan View Post
1 inch per 8 feet is wrong.

Your whole line should be 1 inch per 4 feet.


Unless you're using the metric system.
I was thinking the same thing.....

I don't see where the OP says he is in Canada...

Even if 1/8" is min.....I wouldn't do it....especially with the stuff I put down the head......you want that stuff heading to the street post haste.....let it sit in the pipe too long and it could cause major carnaige....(I gotta lay off the hot salsa)
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Old 12-30-2012, 10:36 PM   #9
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1 foot per 8 feet drop on final leg


Although many plumbers up north here interpret the code as any 4" pipe can be graded at 1/8" per foot, it's technically only the building drain which, paraphrasing here, "Connects the building sewer to the furthest branch." So in theory, everything in the building is going to be running through the building drain so nothing should be sitting there for very long.

Since what he's most likely doing is just tying a 4" branch into his main line to pick up a bathroom, he SHOULD be graded at 1/4" per foot.

As far as his location, since I'm under the impression the UPC doesn't allow 1/8" per foot grading, and you guys aren't fond of ABS pipe, I'm assuming he's probably from up north. But that's just an educated guess at best.
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Old 12-31-2012, 12:19 AM   #10
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1 foot per 8 feet drop on final leg


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Originally Posted by joeplumber85 View Post
Although many plumbers up north here interpret the code as any 4" pipe can be graded at 1/8" per foot, it's technically only the building drain which, paraphrasing here, "Connects the building sewer to the furthest branch." So in theory, everything in the building is going to be running through the building drain so nothing should be sitting there for very long.

Since what he's most likely doing is just tying a 4" branch into his main line to pick up a bathroom, he SHOULD be graded at 1/4" per foot.

As far as his location, since I'm under the impression the UPC doesn't allow 1/8" per foot grading, and you guys aren't fond of ABS pipe, I'm assuming he's probably from up north. But that's just an educated guess at best.
To clarify the UPC- per table 7-5, horizontal 4" drainage pipe can carry 216 DFU's at 1/4" per ft. Foot note 5 says "for 1/8" per ft. slope, multiply horizontal fixture units by a factor of 0.8" thereby reducing the DFU load to 173 (hard to max out a 4" in a house)
Sec. 708.0 gives the standard "conflict with structural or sewer depth" exception for 1/8" vs.1/4" so you must try to maintain 1/4"/ft
However, my inspectors don't give it a second thought.
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Old 12-31-2012, 09:30 AM   #11
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1 foot per 8 feet drop on final leg


After all this, what I really want to know is why do you keep working with this person? You a glutton for punishment?
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Old 12-31-2012, 10:03 AM   #12
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1 foot per 8 feet drop on final leg


The only way I would allow 1/8" per foot is in commercial roof drains for storm water evacuation, where there is no human waste involved. 1/8" is too low slope for people like chili pepper ddawg16, of course I guess you could calculate thrust due to the explosive pressure wave...........
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Old 12-31-2012, 11:56 AM   #13
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1 foot per 8 feet drop on final leg


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After all this, what I really want to know is why do you keep working with this person? You a glutton for punishment?
Imagine the punishment if all us "pros" were in one room- not just a chat room. We'd have to draw lots to see which code to use, then pick a lead guy, decide on a grunt, oh- and who's going to sign the check?
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Old 01-02-2013, 11:57 AM   #14
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1 foot per 8 feet drop on final leg


> the code also states while minimum grade is acceptable, increased slope is recommended whenever possible

Now I'm completely confused.

OK let me put it another way. Min according to code for 4" abs is 1/8" per foot. Is there a max according to code? What's your recommendation (opinion) on optimum?
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Old 01-02-2013, 12:48 PM   #15
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1 foot per 8 feet drop on final leg


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> the code also states while minimum grade is acceptable, increased slope is recommended whenever possible

Now I'm completely confused.

OK let me put it another way. Min according to code for 4" abs is 1/8" per foot. Is there a max according to code? What's your recommendation (opinion) on optimum?
1/4" maximum grade- also optimum.

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