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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.

Layout

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?

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  • Consider running three Pex lines. Hot, Cold, and Hot Return. Use a hot water re-circulation pump so you don't have to wait forever for warmer water, and to keep the lines from freezing i the time between when it starts getting cold and when you're ready to blow it out. Keep the three liens in contact and insulated to save energy. If one line breaks later, use the cold for return. It's nice to have fresh cold water sometimes, I have hot water in my garage wash sink, and it is SO worth it. You can extend your 'warm season' and wash your hands in the freezing winter! its great! – Billy C. Jun 18 at 9:15
  • Also, to save energy, you can have the recirc pump controlled by motion sensor in the garage so it only pulls hot water in there if someone's around to use it. – Billy C. Jun 18 at 9:15
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    While you and your family will be quite aware of the garage sink drain arrangement, it's safe to assume that this knowledge will be immediately lost for the next residents of the house. While I'm personally not too concerned about a bit of turpentine, etc, being washed out directly into the ground (unless you or your neighbors are on a well), many people are. Also, if this is detected by an inspector, you'll probably have to change it to drain into the sewer/septic system, so you may as well plan on that from the start - it'll be cheaper in the long run. – FreeMan Jun 18 at 12:43
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    To bypass the sink drain requirement, don't install a sink. Install a garden hose spigot, and use a wheeled, portable wash basin. Those don't have to be plumbed in as they are not fixed equipment – Billy C. Jun 18 at 13:33
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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...)

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  • I'd add putting tape around any pex crimps you do underground. The last time I had a plumber in to do pex underground he vinyl taped the crimp rings. – Fresh Codemonger Jun 17 at 22:55
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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 . . ."

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