How deep should sewer pipe be when exiting slab?

[The Famous Grouse]

Question everyone. We're starting on a cabin next spring on my hunting property in East central Minnesota. It will be a 30x60 pole shed, half living space, half garage. Full slab underneath everything.

Obviously, this is in a rural area. I won't have a septic system installed for some time due to cost, but of course I want to install all the sewer/drain pipe below the slab during construction. I'll plumb under the slab for a kitchen sink and a bathroom with sink, shower, and toilet.

My question is this. I'm planning on running a 4 inch pipe out beyond the edge of the slab and capping it off. I'm assuming that any pipe that goes out of the slab has to be below the frost line or it will risk freezing and this applies to waste pipe. Correct?

Assuming above is correct, how far below grade does this pipe need to be at the point that it exits the slab? Does it need to be all the way below the frost line at this point?

Or do you just let the natural 1/4 inch per foot drop play out and it ends up wherever it ends up, and then put on like a 45 bend at the slab edge to start dropping quickly to get below the frostline?

Any other advice, "be sure you do", or other suggestions appreciated.

Thanks.

Grouse

[MNice]

Hey Grouse, just get the pipe at least 1' below slab. On a future septic you will be OK. Better to be high than low, depending on septic design. My buddy's cabin is about 20 miles east of Mille Lacs and we have had zero problems, built in 91.

MNice (IDO board) master plumber, PM if you want to discuss

[2beast]

Timely post

I am planning something similar

[Splinter Puller]

If you want to ensure freeze proof operation you should run all the sewer below frost depth. In your case... are you letting the structure go unheated in the winter? if so.. you will want to winterize the drains and not use them in the winter.

[The Famous Grouse]

Splinter Puller said:

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If you want to ensure freeze proof operation you should run all the sewer below frost depth. In your case... are you letting the structure go unheated in the winter? if so.. you will want to winterize the drains and not use them in the winter.

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Yes, structure will be unheated in the winter. While we MAY use the cabin for the occasional winter weekend, my plan was to minimize the use of the septic by reverting to the outhouse during these weekends. I'll probably rig up a "slop bucket" drain under the kitchen sink so we can haul in our water during these weekends rather than un-winterizing the well.

MNice, does your buddy use is cabin during the winter at all?

To elaborate a little, my property is 80 acres and hopefully soon to be 120. I'm only the second recorded owner of this land. I'm completely landlocked, the only access is deeded access across a neighbor property via a 1/2 mile private road.

There is no electricity and probably never will be as my rough estimate from the co-op is over 10,000 to run wire out there. Never going to be possible at that rate, so I'm planning a combination of solar and a hard-wired generator.

The main thing I'm trying to figure out is should I go for for a situation where everything is freeze proof and therefore I can use the cabin in the winter, or is that going to be way too expensive and complicated? I would hate to get everything built and then find out, well, if you had just done one or two little things, you could have had an all season cabin, but now you're hosed because it can't be fixed.



Grouse

[MNice]

Grouse, yes, we are up there a lot in the winter and septic gets used, then winterized with RV antifreeze when we leave. A properly pitched drain will not freeze, since there is no water standing, plus once the septic is installed, the septic itself puts out a lot of heat. Depending on conditions, if you have the pipe below the frost line, (5' in central MN), it's almost impossible to get a septic in that deep without major troubles.

[Curlycherry]

You'll be well served to put pipes below frost line. That way you are 100% covered for any use you may want.

[goaliedad]

MNice said:

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Grouse, yes, we are up there a lot in the winter and septic gets used, then winterized with RV antifreeze when we leave. A properly pitched drain will not freeze, since there is no water standing, plus once the septic is installed, the septic itself puts out a lot of heat. Depending on conditions, if you have the pipe below the frost line, (5' in central MN), it's almost impossible to get a septic in that deep without major troubles.

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What he said- drains are not below the frost line.

[blackhat]

Care to elaborate on those major troubles? Let's assume for now that he is talking about a simple sewage holding tank and not a 2 compartment septic with a pump out.

[fixtureman]

If you put the pipe 5 ft deep your tank will be about 4 ft below grade and the bottom will be somewhere around 10 ft deep. Is you have to pump it you will need to dig down 4 ft