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I have a new manufactured home in the greater Seattle area. Our frost line is at 12” and the home sits on concrete runners.

My contractor ran a common trench for our utilities, power and cable and water.

We are supposed to back fill the house a bit but I’m not sure how much, but I’m trying to find the right way to bring plumbing in.

One plumber said they would just put insulated pex on and pass it straight in above the runners. Another said he would put a valve box in and a main shut off first.

Neither addressed frost concerns. I asked online and everyone said the line should come up through the concrete not above it.

What’s the best way to solve this properly?

  • That open trench is WAY too close to that stack of blocks, if they are in fact carrying the load of part of the house. – Ecnerwal May 19 '19 at 22:52
  • it is scarier to think that the blocks are placed on dirt without anything underneath to spread the load to a larger area – jsotola May 20 '19 at 0:28
  • The house is on a concrete slab (runners) 5" thick. – MorePyPlease May 20 '19 at 16:46

As for the best way to solve this properly, I'd say "put the house on a foundation" but that's clearly not what you are looking for.

Digging the trench to the point(s) where the water and sewer connect and then building an insulated box with a hard skin to keep animals out of it (cementboard or metal) to contain the pipes running vertically. Otherwise you're into the godawful failure-prone land of wrapping things in heat tape and insulation, and hoping you don't have a heat tape falure that either freezes your pipes or sets things on fire...

  • The house is on a 5" concrete runner pad. How would you handle ingress into the skirting? Would you put a hole through the concrete or just run perpendicular and backfill over top? The water connection hose bib is roughly 18" inward from the house perimeter on the opposite side of the house from this location. – MorePyPlease May 20 '19 at 20:43
  • You keep using the term "runner" - what do you mean by that? Is it a slab, or is it two narrow slabs? In any case, if you put a slab down, you should have dug the waterline trench before putting the slab down. Since you didn't do that, you have created a problem for yourself that will be more difficult/expensive to resolve. You might be able to core a hole in the slab and down below frostline, and then hire a horizontal boring company to try and hit that from your waterline trench. If you do mean "narrow slabs" you might be able to dig most of it by hand, awkwardly under the house. – Ecnerwal May 20 '19 at 22:25
  • Yeah, this is the industry standard name for it. You can read more about it here under the 'runner foundation' heading. mobilehomesell.com/mobile-home-foundation-types I ended up hiring another plumber to come take a look at it. He ended up coring a hole in the slab and bringing the water under the house through the slab and then running insulated pex to the hose bib. – MorePyPlease May 20 '19 at 23:27

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