Soil pipe depth requirement

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mreeves

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Is there a depth requirement for a soil pipe that runs outside a building? Old house with an addition on the back and an exterior 3" vertical wasteline from the second floor. Some previous owner installed and uninspected half bath and ran the soil pipe (schedule 35 PVC) across part of the yard and tied into the base of the exterior verticle waste stack that goes into the basement. I want to enlarge the bathroom and also bring the plumbing work up to code. To maintain pitch I will only be about 10" below grade when I come thru the foundation wall of the addition. Is that deep enough?

My other option is to go thru an 18" thick stone wall with a 3" line into the basement and install an ejector pump setup to get the waste up and over the basement area the would need to be crossed.
 
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mreeves

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Location is New Jersey. so yes it does freeze. Water supply lines need to be 36" below grade here.
 

hj

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depth

In many cases, you do not have any control over the depth of the pipes, freeze area or not, because you cannot go lower than the pipe you are connecting to, less the required pitch by the time you get to the plumbing fixture location. I have installed sewer lines 3" below the ground because that is where it wound up by the time I installed the lateral run to the addition.
 

Cass

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Most sewer lines never freeze no matter the depth as the air temps inside tend to be above 32F reguardless of the outside temps.
 

Gary Swart

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Another reason not to worry about the freezing, a sewer line does not contain water except when something is draining, and the somewhat warm water is moving. It would have to be extremely cold before it would freeze moving water.
 

hj

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freezing

If the pipe is shallow, then the surrounding ground can be below freezing temperature. Moving water will freeze if it stays in contact with the cold long enough. (Ever seen a picture of a frozen waterfall, or river?) As long as the plumbing is working properly it will not freeze, but if a toilet or faucet is leaking then that small flow of water will freeze. It will be cumulative so as it freezes it will create a dam causing water to accumulate and freeze behind it and eventually fill the pipe with ice.
 

Jadnashua

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Insulation slows the transmission of heat. A sewer pipe that does not have anything running through it basically has no heat in it to move. Anything that moves through it is only transitory, and wouldn't heat it up enough to make much difference with trying to slow its dispersal with insulation. So, you've got cold ground with an unheated pipe going through it, so what heat would the insulation slow? My unprofessional thoughts.
 

Cass

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I have taken 2" of insulation and placed it on bare ground that had been exposed to 10F air for a week or so. Covered it with plastic and 4 days later could shovel the dirt.
 

Jadnashua

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Yes, but depending on where you live, the frost line could be way down there, so again, it probably wouldn't matter much.
 

hj

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rshackleford said:
the insulation would slow the loss of the heat from the earth to the atmosphere.

i have been told that a 2" piece of dow board is equivlant to one foot of earth cover. i guess i could do the math, but does anyone else have thoughts on it.

That may be, but eventually, and sooner rather than later, the chill will penetrate the Dow board and everything will be in stasis as far as the temperature is concerned, unless, that is unless you can find a way to introduce heat into the ground inside the Dow board.
 

Rshackleford

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yes, but....

by the same reasoning the frost would just travel down and down and down. if the earth did not have an ability to hold heat and an insulating value the earth would freeze until the heat of the core stopped the frost. if the dow board insulates the equivilant of an certain profile of earth, the frost will penetrate that much less. the heat from below will be "stopped" by the cumulative r insulating value of the dow board and earth. if 2" dowboard is equivilant to a foot of earth and over the period of a typical winter the frost reaches to four feet, then the pipe could be placed at three feet with dow board and not freeze.

if your statement were true there would be no frost line.

around here some pipeline companies will rip an expected pipeline route with a cat. the extra r value created by adding air to the soil will keep that pipeline route from freezing throughout part of the winter.
 

Cass

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I had a customer a few years ago with a water line 12" deep that in the 30 years he lived there swore never froze, hard to believe but.... Our frost line here is 24"-30" and required depth for water lines is 42" Min.
 
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