IPC minimum depth to drain pipe under basement slab

[Mariposuerte]

According to IPC is there a minimum depth to the drain pipe under a basement slab? My Dad told me 4" minimum below the slab but I can't find that in the 2018 code. Anyone know what section IPC requires depth to drain pipe under slab?
Thanks! John

 

[James Henry]

You have to find your county or city code for that answer. Even some cities have their own code, that's why you can't find it in the IPC.

 

[Sponsor]

 

[Mariposuerte]

Our cabin build is in Costilla County, Colorado and they just use 2013 IRC. No city or other code required...but CO plumbing code also incorporates IRC and they do the only inspections. I will see if I can find anything in IRC regarding required depth of drain pipe below slab.

 

[Mariposuerte]

Well maybe 2013 IRC was not the right year b/c I couldn't find that edition, but I did find 2015 IRC and it basically says the same thing as IPC almost word for word. But I didn't see any requirements for minimum depth below slab for drainage piping. If anyone has any leads, let me know. I will keep looking.

 

[James Henry]

The reason the IPC doesn't specify a specific depth is because the frost line is different all over the country. I found my local county plumbing code online but it was by accident. Just call your local building department, if that doesn't work call some local contractors and ask them.

 

[Mariposuerte]

This is in my basement under that slab which will be around where the footings are...over 5 feet deep which is below frost line so that won't be an issue. Our neighboring county has some code guidelines and that is where I have pulled most of my information. (I will check that) I am running my basement sewage line about 24 feet through a 3" PVC (1 bathroom group plus utility sink) to ejector pump basin. With a 1/8" per foot drop that puts me pretty deep for my ejector pump basin if my high point is minimum 7.5" below the floor. I can make it work by framing out the ejector basin and putting it lower but was wondering what the requirement was in case I can come up with a plan B. I can ask our contractor who is doing the basement/slab and maybe they know or can point me to someone who does.

 

[John Gayewski]

No minimum depth that I'm aware of. Usually you want bedding under your concrete which would typically be 4". That's what most designs specify. I know in upc your can't have pipe touching concrete. The pipe has to be protected.

 

[Jeff H Young]

we sometimes start out just below the slab on interior a bathroom addition or something a few inches top of pipe to bottom slab . this is warm country . less digging. never a problem .

 

[Mariposuerte]

Thanks all. That is helpful. IRC does require 4" of bedding below the slab but I wasn't sure if that included above the drain pipe since it only covers a 3" wide pipe. I will need to drop the ejector basin around 1-2 inches anyway unless I move it a lot closer to the bathroom (which I could do by re-arranging the utility room) so I might as well adhere to the 4" bedding rule and go a bit deeper with the basin. I will get eyes on the site next week when we will need to dig out the ejector basin so if adding 3-4 inches of depth isn't an issue then that probably makes the most sense. It shouldn't be an issue unless we hit rock...it is in the mountains but the build site has lots of soil and we had no issues with the septic and well install (and soil report) but that doesn't guarantee us anything. I will talk with our basement contractor today to see what they typically have done with other builds in the area to see if I can get away with 2 inches of bedding at the high point then maybe I will consider altering the basin location.
Thanks again...John

 

[Jeff H Young]

As far as I know it can rest in native soil here over excavating and a minimum amount of fill is not required but can be depending on circumstances if we have a solid bottom of trench we can lay right on top . just my practice over the years but we have had specs requiring a minimum amount of sand .

 

[Mariposuerte]

We have done that in Texas frequently as well but my experience is mostly in areas with no inspections. It looks like this is a new requirement in IRC 2015 code...IRC 506.2.2 Base says to use 4" of sand/gravel base course under the slab BUT you can pour slab on native soil if it is well draining or sandy-gravely Group 1 soil according to United Soil Classification System. We have well draining soil at our site in CO, but I am not sure how it will look 5 feet below grade. We had Group 1 soil classification from our septic test pit supposedly dug to at least 8 or more feet in depth (reported on the engineering diagram for septic system) so maybe we won't have to have 4" of fill. Then maybe I can just use 1.5" of cover or so above the high point of my 3" drain and my ejector basin could be at or just under floor level. I will talk to our basement contractor this afternoon and will see whether we have fill or going on native for the slab. I was thinking I could do this even if we had 4" of fill because I don't see that its prohibited per IPC/IRC, but I will see what my contractor knows about what is done locally in the CO high country since I don't see a direct requirement in either code. The plumbing inspector probably won't care about the concrete as long as my pipes aren't touching it and there aren't any other foundation or slab inspections, just a county "requirement" to follow IRC 2012 or so...don't remember the exact year but it is prior to 2015.
Thanks for the input.

 

[Jeff H Young]

I think even though there is 4 inches sand there isn't any problem having a pipe displacing some of it. sure wouldn't hurt to ask foundation contractor his take on whether to expect inspector having a problem