Slab Leak? We Rerouted the Line Through the Attic Instead of Breaking the Slab

A leak under your slab sounds like a worst-case scenario: jackhammers, torn-up floors, and a concrete patch through the middle of the house. Sometimes that's the only route. But often there's a better one — go over the top instead of through the floor.

On this job, a diagnostic visit found a pinhole leak in the copper hot water line running under the slab between a bathroom vanity and the shower. Rather than cut the slab open, we rerouted the line: new pipe up through the wall, across the attic, and back down — and the leaking copper was capped off and retired for good. Here's how the job actually went.

What a Reroute Actually Is

A reroute doesn't repair the leaking pipe. It replaces its path. We open small sections of drywall behind the fixtures the line serves — here, behind the vanity and the shower — run a new water line up into the attic and back down the other side, and cap off the old copper where it dives under the slab.

The buried line stays buried. It just stops carrying water, so the leak stops with it. The tradeoff is a couple of drywall openings that are simple to patch, versus saw-cutting and repairing a trench through your slab and flooring. For a single line serving a bathroom group, it's usually the least destructive fix by a wide margin — and it's the same thinking behind many whole-home repipes, where new lines are routed overhead instead of under the house.

Step One: Prove Which Line Is Leaking

You don't reroute on a guess. With the water off, we cut the candidate lines and blew air through them — air escaping tells you which run is compromised. On this job the test pointed to the middle line of the three: confirmed, not suspected. That line got marked for capping, and everything else stayed in service.

This step matters. Rerouting the wrong line leaves the leak under your slab and adds a brand-new pipe you didn't need. Diagnosis first, demolition second — in that order.

Step Two: Cap the Bad Line and Build the New Path

With the leaker identified, we capped the abandoned slab line and built a new manifold under the sink to feed the vanity from the new overhead line.

The transition from the home's existing copper to the new pipe happens with Uponor-to-copper adapters, pressed onto the copper. And here's a detail that separates a joint that lasts from one that weeps: the copper gets cleaned with sand cloth until it's bright and shiny before anything is pressed onto it. A clean surface means the fitting's O-ring seats properly instead of getting nicked on oxidation and debris. A minute of patience per joint, and it's not optional.

Why the New Line Is PEX A

The new run is PEX A — Uponor pipe joined with expansion fittings. The pipe and an expansion ring are stretched open with a tool (on half-inch, we typically use eight or nine expansions), the fitting goes in, and the pipe shrinks back down and seals around it. We hold each joint for about 20 seconds while it firms up; after roughly a minute it's fully sealed.

Two reasons we like it for this work, both of which you can see in the video:

• Full-port fittings. The inside of a PEX A expansion fitting is the same diameter as the pipe itself — or very close. With PEX B, the fitting's inside is noticeably smaller, so every fitting costs you some flow. Full-port means the shower doesn't know anything changed.
• Flexibility. PEX bends. A rigid material run through an attic and down two walls would mean far more cuts, joints, and fittings; flexible pipe snakes over the top cleanly.

Step Three: Tie In, Strap It Down, and Pressure-Test

Once the downstairs portion was tied together, the crew connected the PEX lines in the attic, strapped and supported the new pipe, and hooked up the angle stop and supply line at the vanity.

Then the part that proves the job: we turned the water on and let it sit under pressure for about 20 minutes. Hot water came instantly at the fixtures. One of our techs stayed in the attic for about ten minutes watching the new joints — no leaks. The last step was insulating the attic piping, and the job was done.

Frequently Asked Questions

My pipe is leaking under the slab. Do I have to tear up my floors? Not necessarily. A reroute bypasses the buried line instead of digging to it: small drywall openings are cut behind the fixtures, a new line is run up through the attic and back down, and the leaking line under the slab is capped off. On the job in this post, the homeowner avoided cutting the slab entirely.

What is PEX A, and how is it different from PEX B? PEX A is joined with expansion fittings: the pipe is stretched open, the fitting is inserted, and the pipe shrinks back and seals around it, fully set in about a minute. Those fittings are full-port — their inside diameter matches the pipe — so you don't lose flow the way you do with PEX B, whose fittings are smaller inside than the pipe.

What happens to the old leaking pipe under the slab? It's capped off and abandoned in place. It no longer carries water, so the leak is permanently out of service — and because nothing needs to be dug up to remove it, it simply stays where it is, empty.

How do you confirm the reroute actually fixed the leak? With a pressure test. On this job, we turned the water back on for about 20 minutes, confirmed hot water arrived instantly at the fixtures, and kept a tech in the attic for roughly ten minutes watching the new joints — no leaks. Since the old slab line was capped and carries no water, the original leak is gone by definition.

Got a Slab Leak in Tampa? Let's Look at Your Options First.

Before anyone cuts your slab, the line should be diagnosed and the routing options weighed — a reroute through the attic is often the cleaner fix. Sewer Studs Plumbing & Drain handles water repipes and reroutes across Tampa Bay. Call (813) 680-2284, Monday through Friday, 8 AM to 5 PM, and our Tampa plumbing team will tell you straight which route makes sense for your home.