Is 1/4" drop in 10' enough.

[John White]

I plan on putting underground pipe to capture water run off on the roof of my building. It will be using smooth pipe. In a 80' run how much drop would I need? I usually like to have 1" in drop in 10'. But am sort of limited in this case.

 

[LD1]

I think 1/4" is fine. With smooth pipe, any drop at all and water will flow. But it is really hard to be that accurate when trenching in pipe...

 

[radioman]

I use a 4 ft level and make the bubble on one side of the center and its more then enough to make sure its flowing downhill. I don't measure via inches . just a level.

 

[wolftree]

Tape a pencil crosswise on the downhill side of your level to give you a 1/4 inch by whatever length your level is.

 

[LD1]

Tape a pencil crosswise on the downhill side of your level to give you a 1/4 inch by whatever length your level is.

Unless he has a 10' level, that wont be enough for what he is wanting

 

[greasemonkeyok]

I plan on putting underground pipe to capture water run off on the roof of my building. It will be using smooth pipe. In a 80' run how much drop would I need? I usually like to have 1" in drop in 10'. But am sort of limited in this case.

The rule of thumb I am familiar with is 1/4" per foot. But it actually depends on the amount of water that will be drained to be precise. A more involved answer can be found here:
What is the recommended slope for drain pipe carrying excess rain water from pool and deck around pool

 

[MacLawn]

Grease, that link only took me to the question. Anyway, I've always kind of leaned to the 1/4" per 10' system. I know volume will make a difference, and pipe size. John White, how big is ye pipe? For 80', 4" pipe might be a tad small, but I don't know. I'd feel better with maybe 8" for that length. I actually need to do something very similar for runoff from me house, but only have about 40' to go.

 

[greasemonkeyok]

Grease, that link only took me to the question. Anyway, I've always kind of leaned to the 1/4" per 10' system. I know volume will make a difference, and pipe size. John White, how big is ye pipe? For 80', 4" pipe might be a tad small, but I don't know. I'd feel better with maybe 8" for that length. I actually need to do something very similar for runoff from me house, but only have about 40' to go.

I get the answer below the question on that link, which refers to Table 1106.3 "Size of Horizontal Storm Drainage Piping" from the International Plumbing Code.

If you have commercial experience then you way ahead of me, my experience is limited to doing my own drains.

 

[RickB]

Unless he has a 10' level, that wont be enough for what he is wanting

Actually, it will be more than what he is wanting. But I'd want no less than 1" in 10' of run myself. 1/4" in 10' won't eliminate low spots in a trench.

 

[LD1]

Actually, it will be more than what he is wanting. But I'd want no less than 1" in 10' of run myself. 1/4" in 10' won't eliminate low spots in a trench.

Thanks for the correction. My fingers and brain werent on the same page. Happens sometimes

 

[toddbailey]

I would try and shoot for 1% slope, you would need 1 1/4" in 10'

 

[EddieWalker]

Is this clean rain water or will their be silt mixed in with it? If it's clean water, then you should be fine. If you have silt, or anything at all mixed with the water, you will have some build up. How big is the pipe? If it's too small, the build up will restrict flow. I would think four inches or bigger should work, but that depends on how dirty the water is. I've seen 12 inch culverts without enough slope in them completely plug up.

Eddie

 

[John White]

I plan on using 4" thin wall, will drain off metal roof, approximate 2000 sq ft. Will fall into a D box with a screen . If D box overflows over, no big deal. It will just run out on ground. Actually the building is 4000 sq ft. 50'X80'. I plan on coming across 50' make a L and go 80' ft, another D box there with a T into the L. Come off the other 50 corner and T into existing line, and drop about 2' and go about 30 ' into a 500 gal tank buried. Talked to the State Soil and water district. They said if we have a 1" rain, it will produce about 8000 gal of water. (doesn't sound right to me) Seldom do we have a rain like that, but if we do and the pipe wont handle it, it can just run off. (tank certinley wont hold that much)

 

[LD1]

I plan on using 4" thin wall, will drain off metal roof, approximate 2000 sq ft. Will fall into a D box with a screen . If D box overflows over, no big deal. It will just run out on ground. Actually the building is 4000 sq ft. 50'X80'. I plan on coming across 50' make a L and go 80' ft, another D box there with a T into the L. Come off the other 50 corner and T into existing line, and drop about 2' and go about 30 ' into a 500 gal tank buried. Talked to the State Soil and water district. They said if we have a 1" rain, it will produce about 8000 gal of water. (doesn't sound right to me) Seldom do we have a rain like that, but if we do and the pipe wont handle it, it can just run off. (tank certinley wont hold that much)

4000 sq ft @ 1" of water
4000/12 = 333.33 cu ft of water.

There is 7.46 gallons of water in each cubic foot.

So, 333.33 x 7.46 = ~2500 gallons of water.

Yeah, they are a little off, but its still alot of water. It dont take much off a roof to fill a large volume.

A 1/4" average rain will overfill your 500 gallon tank.

 

[CurlyDave]

When I built my first house in CA, I had a straight roof edge which was 40' long. I sloped this edge at 1/8" per foot so that the gutter could be mounted just under the roof edge and still drain to one end.

This worked very well, but must be addressed at the framing stage of the building. All of my friends with building experience thought it was a crazy idea, but all were impressed with how well it worked. The only real issue was that sheet rocking the inside of that wall was unique because 1/8" per foot is 5" over 40 feet.

 

[greasemonkeyok]

When I built my first house in CA, I had a straight roof edge which was 40' long. I sloped this edge at 1/8" per foot so that the gutter could be mounted just under the roof edge and still drain to one end.
...t.

I had a builder do something like that about 35 years ago, except his wasn't intentional.:laughing:

Seriously though, we had a German carpenter come in to install bi-fold doors on a closet, and he knew exactly how to do it without drawing attention to the slope.

 

[MacLawn]

Now Curly, that's thinking outside the box! Slope ye whole roof so ye don't have to slope ye gutters. I'm good at coming up with hairbrained ideas, but you might have topped even me! Now, I ain't calling ye idea hairbrained, I'm calling my ideas hairbrained.

Back to the pipe drain - I'd still want to go with about 8" pipe. I was thinking clear water, and if so, 1/4" per 10' should be fine, IF pipe is layed down right. Aw, go ahead and make it 1/2" slope per 10".:laughing: