This is the same question I posted a few weeks ago, but I've more info now, and I'm hoping you guys are so very bored you're willing to read this description and give me tons of free advice.

I've a 3 bed/2bath single story house with slab on grade foundation in San Deigo, California. The home was built in 1970. I'm moving the kitchen sink to an island, and I'm looking for advice on how to do that. I've had my sewer pipes inspected/located (they're in ok condition), and I'm trying to decide which way to dig the trench that needs to provide water/sewer/electric to the island. Importantly, I will probably repipe the whole house as part of this remodel (e.g., currently I've copper pipes in slab, and I'll change it to PEX in the attic).

Floor Plan Image----> [ibb.co]

In the image, you can see the proposed kitchen island in (highlighted in pink, measuring 8 feet long). The existing sewer pipe is also marked in pink. Everything else in the image is existing. I think (think) I'll either run the trench along the purple arrow, or the green arrow. Which way do you think will be cheaper/less problematic based on the extremely limited info I'm giving you? Here are my thoughts.


Purple arrow:

Its about 20 feet from the island to the destination. The sewer pipe I'd tie into is 2" diameter ABS. Water/electric and venting will be via the wall just past the sewer pipe (there's already one vent in this wall). As an alternative to installing a proper vent, I may install an air admittance valve in the island.. which may or may not be kosher in San Diego CA.

The purple arrow means the trench will have to be cut through/into the foundation-footer (aka continuous foundation) that runs around the perimeter of the home's concrete slab. Cutting into this part of the foundation doesn't make me happy, I'm assuming it's much thicker than the concrete in the middle of the slab (am I wrong?). Maybe cutting this part of the foundation is done all the time and I'm overthinking it?

Or.. the Green arrow:

Its about 15 feet from the island to the destination. The sewer pipe I'd tie into is 4" diameter ABS. Water/electric and venting will be via the existing wall that the trench will pass under on it's way to the sewer pipe. This wall is not loadbearing and has (I hope) pretty limited utilities in it (two electric switches, water inlet for toilet, and a vent.. that is probably for toilet). The toilet (not drawn) is squarely in the way of the trench (its directly under the head of the green arrow).

The green arrow seems stupid at first glance, but maybe it's not that big a deal to completely demo and rebuild the wall the trench will go under? Plus the green arrow option ties into a bigger sewer line (4" diameter).. which.. don't laugh at me please.. maybe allows me to magically wet-vent the kitchen island by using an oversized drain (3 - 4" pipe) from the kitchen island? I've gone blind reading about loop vents and foot vents, I really just want to use an AAV.

i would go green.
i would stay away from the foundation/footer at all cost.

Purple goes to your existing kitchen sink line - Correct ?

Normally this sewer line would not have been run in the footer. Too much rebar, hold down bolts etc. in the way.

This should be a pretty easy tie in if it is not in the footer.

No toilet etc. in the way. Could be a lot of fittings at the other tie in location.

You had it traced so I could be wrong.

Thanks Curly. Correct - Purple goes to my existing kitchen sink line (sewer).

I agree this sewer line is likely well away from the footer and easy to tie into. But its the electric/water that I'm worried about. Electric/water would likely come from the nearest wall (i.e., the shared wall with the garage). So I'd have to dig the trench an extra 3 feet past the sewer line to this wall. This is a load bearing wall that probably has a footer. I don't like the idea of cutting.. or even putting a notch in this part of the slab. So.. I'm leaning towards the green route.

Can the purple line tie into existing kitchen sewer line between garage access door and interior wall that runs periductular to garage door access wall ?

Pick up water/electrical off interior wall ?

If you go green that floor in the bathroom is going to really be torn up. Are you also remodeling bathroom ?

Curly - good point, thanks! Yeah.. if I take the green arrow route, then likely we'll remodel the bathroom too.. which is why the wife knows nothing of this conversation.

FYI - I intend to demo the perpendicular wall (interior wall, pic below) you mention and push the front door out ~ 3 feet to be flush with the wall that is shared with the garage. If I do as you suggest, I'd have to leave a portion of that interior wall just for purpose of pulling water and electric.. or leave the front door where it is. I'll think about that.

Pic of moving front door --> [ibb.co]



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