Is putting a pex tube underground and then through a concrete slab OK?

Question

I have a house with a basement and I'm building a garage about 50 feet away in the backyard. The garage will be on a concrete foundation and I want to run both power and water out there. (I want the water for a mess sink and an exterior hose connection.)

My plan is to lay this pipe before the footings/foundation are put in. The water pipe will switch from copper to PEX inside the house, and the two pipes (electrical, water) will exit the house slightly underground, and then go deeper (probably 2-3' deep). They'll run up to where the garage footing will be, through a sleeve (4" pipe probably) that goes through the footing, and then be laid under the concrete foundation, poking up as close to the wall as I can. Because I'm relying on the water pressure from the house I was not planning on grading the water pipe, just running it level.

I do intend to install a blowout valve for the water pipe. There will be a ball valve in the basement of the house for this pipe, then the blow out connector, and then it will convert to pex and exit the house. In the garage, it will T under the foundation, one part coming up through the foundation, the other exiting the back side of the structure, through another 4" sleeve, and go into a below-ground graveled chamber with a ball valve shutoff, and a lawn sprinkler box top.

There will be no sewer connection, the interior sink will drain to a pipe that goes under the concrete and feeds out to that same gravel box, through the same sleeve. I know this precludes using the sink for things like washing out paint brushes and other chemicals; that's okay.

My first question is does anything sound off about this plan?

My second question is can I use PEX tubing for these water lines? I know you can't use PEX tubing where it will be exposed to sunlight; but I think I can bury it without problem. Can I also run it directly up through the concrete foundation without some additional protection?

Answer 1

Sleeve It

When running any tubing (PEX, ABS, PVC) through concrete you need to de-couple it, Even 6mil plastic suffices, but sill guard is better. A tubing sleeve (e.g. 1.5in ABS) like you propose through the wall, is good too.

Hot and Cold

You can run PEX under ground. I have done this successfully. Hot and cold to the exterior, then cold to an out building. But a hot leak can get expensive, so I always keep it shut off except for a short period when I need it.

Avoid Connections

I keep the line under the frost line, because here's it's only 2ft deep. Try to avoid connections under ground: get PEX on a roll if you can.

For any turns, e.g. 90deg upward to the slab, consider a wide sweep with the tubing instead, and skip the underground L fitting.

Back-Up Line

Most of the work is the digging, and PEX is cheap. Run a second dry line if your earth moves or you have heavy frost.

Blow Out

The blow-out is great.

You can use any spigot as your blow-out relief; no need for a dedicated blow out valve.

To pressurize or to blow, add a compressor fitting or an air valve (e.g. NPT tank valve) to the PEX.

You can then easily do periodic pressure tests to confirm there are no leaks using just a tire pressure gauge as your manometer.

More Shut-Offs

I also suggest intermediate shutoffs if you are splitting off, e.g. between an outside spigot near the house to a longer run under ground. If you ever have a leak, luck may keep other parts still serviceable.

Shield and Protect

Where it's outside and above ground shield it from UV (sunlight) and mechanical abrasion (lawn mower, and everything kids will do to it...)

Answer 2

In my jurisdiction Dallas TX, PEX is buried just like soft copper tubing used to be, and where the PEX goes through concrete it is sleeved or wrapped. One plumber that I know says this is unacceptable to him. He puts all PEX that is under a slab in Sch 80 PVC or continuous PB (polybutylene). He said that no splices can be buried under a slab. All PEX under a slab or buried at all must be continuous. The one possible exception for PEX is PEX A (Uppanor) splices can be buried but not I think under a slab.

According to this plumber the design should have any PEX under a slab in suitable conduit that would allow replacement by pulling out failed PEX and pushing/pulling in new. In neighborhood I saw him plumb a new house built on a slab left from a burned out house. He abandoned all the copper tubing under the slab. From the valve box just outside the slab he ran a PVC conduit by tunneling under the perimeter beam and up with a sweep 90 through the slab into a front half bath. From there all water lines were inside the structure.

This plumber told me that rodents will readily chew holes in PEX but will not chew into PVC. If PEX is encased in PVC conduit, it would seem to be necessary for rats and mice to be excluded from going into the conduit.

EDIT

A different plumber from the one referenced above also told me that he has installed PEX in conduit for customers willing to pay for the extra materials and labor and he considers this to be the best installation technique.

Five years ago, I talked to a plumber at a new house construction site in my neighborhood who was direct burying PEX prior to a post tension slab being poured. This was premium construction, e.g., exterior 2x6 studs on 16" centers, special design with floating steel stairway to 2nd floor, sealed conditioned attic, two 180 kBTU/h tankless water heaters. . . He replied to my question about conduit for the PEX "nobody does it that way, he had never heard of such a thing, would cost too much, cause problems . . ."

Answer 3

Let's just say that my house and several neighbors houses were built with PEX under ground coming up through the slab.

Every single one or close to every one has had leaks under the slab, or in the slab.