I’m in a situation where a solder connection must be made to 1/2” copper under slab to move hot and cold water to another wall. My question is, would it make sense as an added layer of precaution to slide a copper compression coupling over the soldered joint just in case the solder were to fail at some point in time?

Copper lines under a slab are known to pin hole and leak without you knowing it. if at all possible run copper above the slab to prevent this from happening'

A compression fitting will not fit over a soldered joint coupling.

Many pros here prefer a flared joint over a soldered joint if it's buried and under a slab.

If there is another wall closer one that overshoots the new wall, better to bend that copper to that wall and do another run over to the new wall with an above slab manifold.

Soldered joints underground are a BIG NONO....flared fitting will be a pain in the neck so I say compression fittings.

under slab joints MUST be brazed, not soldered.

yes -- BRAZED




no big deal for an actual plumber

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

I agree with hj and bernabeu as only brazed joints should be used on joining copper pipes under a slab (per UPC Section 1008 c 2).

Also, I suggest putting the copper pipe inside a proective sleeve and if for hot water heavily insulate the pipe as well.



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IIRC, below-slab/below-grade copper must also be Type K (wall thickness), NOT L or M...

I have the 2021 UPC code book in front of me.
I can not locate any code sections discussing this.
All I see is that type M is not allowed underground.
Might be best practice to braze the joints but I am simply not seeing this as code required.

Type "M" does NOT come in "soft" mode so it could not be used underslab unless it had a LOT of joints in it.

M is not allowed inground, under a structure. It can be inground, outside of a structure. [UPC 603.4 Exception]

UPC Section 1008 c 2



IRC:

P2904.12 Underground joints.

Joints in polybutylene (P plastic pipe or tubing underground or under a concrete floor slab shall be installed using heat fusion, in accordance with the manufacturer's installation instructions. Joints in copper pipe or tube installed in a concrete floor slab or under a concrete floor slab on grade shall be installed using wrought-copper fittings and brazed joints.

{Funny IRC permits min Type M copper pipe/tubing but not soldering. Most plumbers I know won't touch M...especially underground!}

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



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