Most of our soil is clay, and slab foundations tend to be more vulnerable to clay's expansion. I'd ask a couple of local architects and structural engineers if they would recommend PEX in a slab.

We did a hybrid. Water comes into house through slab and also to island. But most others run between floors (2 story house).

All drains of course are in slab. I don't think anyone goes around worrying about slab strength. Drains are far bigger than pex of course. Imagine the stability of a piece of plastic held at 60 degrees constantly. Should last forever.

Is your attic really conditioned or semi? No issues with warm water in attic? That sounds like someone is just used to it. The water will be the temp of where the pex is initially. In a typical TX attic, that is hot. Even in a conditioned attic, it is lukewarm.

I have a feeling people get used to water temps based on where they live. Whether it bothers someone is a whole different thing. People in the South are probably way more likely to have a water pitcher in the fridge or use ice.

If you put 3/4" pex in the slab, you can run 1/2" inside it if there is ever a problem. (without tearing up your slab....)

That said - we only ran under slab for islands, the rest is above (although in completely conditioned space)

Thank you all for the helpful responses! I do believe the soil in my area is clay with rock not far below. When I get further in the process I will consult with a structural engineer and I'll post a follow up if I learn anything new. Thanks again!

Pex in the attic for sure. Most of your "Cons" for the attic really aren't an issue other than a potential leak. You have that issue when it's in the slab also and going up to a second floor.

You have to be careful with PEX in a slab especially when crossing expansion joints. I would sleeve. Install in a attic all the way. I use PEX A never had any leaks.

Hi Flo, where are you located? I'm going to have spray foam under the roof deck for attic insulation.

Hi BT, I think the plumber that bid PEX in slab is using an insulated/sleeved viega product. I can't recall the name right now. I don't think the sleeve allows it to be changed out in the future though.

You can add another con to any type of water line in an attic. Condensation. Warm water meets cold air you have it, Cold water meets warm air, you have it.. If you go attic. Insulate both hot and cold water lines good..

Slab. Make sure that the lines can be removed from the slab through a sleeve or something. If not and you have a leak you will not know it until the water has worked its way to an opening. Then it is jackhammer time to find and repair the leak.

Just saying. After watching an apartment complex owner having to jack hammer through concrete and rip through walls of three different units to repair a broken sewer line... NO WAY would I build on a slab.

I've seen insulated PEX, but I don't think that you would be able to pull out the PEX from the insulation and reinstall if it was poured in a slab. What "sleeved" products are available for slab installs that would allow removal? Would I just need to run it through conduit?

You can buy Pre-Sleeved PEX. . Most people use Black plastic pipe, larger PEX sizes etc can be used. Anything that will allow you to slide the Pex through it much like conduit. You do not want to use anything made of metal that will rust out over time.

If I could avoid pex or copper in a slab, I would. You only have to rip up a slab once to know you don't ever want to do it again.

How about another idea - I built my custom house in San Antonio on a slab, and if I ever did it again I would pay whatever it takes to use pier and beam or a perimeter foundation instead, along with using a conditioned crawl space. We haven't had many slab issues, but they are always a PIA to fix. We have had two in-slab water pipe leaks that led to rerouting lines around the leaks. There has also been enough shift in the slab to put cracks in the original tile, and then small cracks again in the travertine that replaced it. The 2nd time they added underlayment that was supposed to prevent cracks, but it was not effective.

Bruce

Hi Bruce, thanks for the comment. I will investigate the options you mentioned. In my area there is rock about 6" below the surface so I hope I could get a solid slab foundation but who knows.

We built our home in Texas and opted for pier and beam instead. We've had too many friends have to deal with water leaks (jack hammer) and shifting foundations. Our rock was 12-18' down and we drilled piers until we hit it. All of our plumbing is in our conditioned crawlspace. Worth every penny spent.

Thanks for the info, ghigpen. I remember reading about pier and beam a while back but it seemed like there were downsides to that as well. Like rodents or moisture getting into the space and causing damage or mold. I'd also have to insulate the whole floor then, right? Maybe a slab that is actually stable and doesn't shift/crack is a fictional thing, but if it existed it seems like being directly on the ground leaves less room for future issues. The only exception would be under-slab infrastructure failing. If I just keep that to drain lines hopefully that would be unlikely though? So many things to consider.

My slab has limestone about 4-5" below the slab, and you still get some shifting. It gets worse when you have long periods of very dry weather.

The old pier and beam construction did not use a conditioned crawl space, so there were vents and other places for rodents and bugs to get in. In current construction they still use piers to support the house, but in most cases there is also a completely sealed perimeter wall, just like a short basement.

Bruce

centraltxguy - our crawlspace is unvented and completely sealed. No rodents can get down there. We have a dehumidifier down there that drains to a drain line. Keeps it nice and dry and we have zero mold. A slab that is not on rock in Texas clay soil is a fictional thing. I highly recommend you watch some of Matt Risinger's videos on YouTube or read his website. He's based out of Austin and is a big proponent of sealed crawlspaces. He's got a ton of useful information on how to build a house right.

https://www.youtube.com/user/MattRisinger

http://mattrisinger.com/

Anyone used a matt-slab or raft slab on grade in clayey soils? Very common alternative to pier and grade beam.

Bruce and gthigpen, thanks for sharing the additional info. I have seen Matt Risinger's blog and actually just did a search after your earlier comments. I saw his video on a sealed pier and beam foundation. It looked awesome, but also very expensive. It was poured piers, a perimeter wall, and then a slab at the bottom with a wood frame deck and closed cell spray foam on the interior of the permitter wall. Wow! I'll ask my builder about it. Not sure if it complicates things, but the exterior walls of this home will be built with ICF.