What’s the under-slab plumbing layout and why does it matter?

The short answer

Your under-slab plumbing is the network of water lines cast into the concrete foundation. Most homes use a trunk-and-branch design: a single hot and cold main, with smaller branches feeding each fixture. This layout determines how leaks are found and fixed. Options like rerouting or epoxy depend on accessibility, so knowing your layout helps you choose the right repair.

Key takeaways

Layout shapes repair: Trunk-and-branch systems often make reroutes easier, while manifold layouts favor epoxy lining.
Leak detection: Knowing where lines run can speed up the $150-$400 detection step and avoid unnecessary slab breaking.
Cost driver: Access costs rise if a line is under a finished floor or in a hard-to-reach spot, so layout mapping is key.
Age matters: Older homes may have copper or galvanized lines that are nearing end of life, making a repipe worth considering.

When a slab leak strikes, the first question isn’t just where is the leak, it’s where do the pipes even go? The plumbing layout cast into your concrete slab shapes every repair decision. This guide walks you through the three most common under-slab designs, shows you how to figure out which one you have, and explains how your layout can change the cost and method of fixing a leak.

What are the most common under-slab plumbing layouts?

Your home’s under-slab plumbing layout falls into one of three common patterns: trunk-and-branch, manifold, or remote manifold. Each pattern affects how leaks are found and which repair methods work best. Recognizing your layout early can keep a $300 fix from ballooning into a $15,000 repipe.

Trunk-and-branch: A single hot and cold main line runs from the water heater, typically under the center of the slab. Shorter branch lines tee off to feed each fixture. This is the most common design in homes built before 2000.
Manifold: A central control panel, often near the water heater, sends dedicated home runs of flexible (usually PEX) tubing to each fixture. Because every fixture has its own line, leak isolation is cleaner, but repairing means opening a greater length of slab.
Remote manifold: Several smaller manifolds are placed closer to groups of fixtures. This shortens the home runs and can reduce the cost of epoxy lining if needed, but adds complexity when locating leaks.

For a deeper look at how layout shapes repair choices, visit our slab leaks hub.

How can I figure out my home’s under-slab layout without breaking concrete?

You don’t need X-ray vision or a jackhammer to sketch your under-slab layout. A few simple observations can tell you whether you have a trunk-and-branch or manifold system. Start with the water meter test, then trace your lines.

Run the water-meter test to confirm you have a leak and to isolate which line is leaking. It’s the fastest free diagnostic you can do. Slab Leak Triage walks you through the steps.
Locate your water heater. If it has two large pipes (hot and cold) leaving it and heading into the slab, you likely have a trunk-and-branch. If those pipes lead to a centrally mounted plastic panel with multiple smaller tubes, you have a manifold.
Follow the fixture stubs. Note where pipes enter the slab near sinks, tubs, and toilets. In a trunk layout, they often cluster along a central line. In a manifold layout, each fixture has its own pipe coming up through the floor.
Check the hot side first. Most slab leaks are on the hot line, so start your mapping there. Use the Hot or Cold Line Identifier to confirm which line is leaking.

This mapping process costs nothing and helps you talk to a plumber with confidence.

How does under-slab layout affect leak repair costs?

Your under-slab layout directly influences repair cost because it determines access difficulty and how many lines need work. Costs vary by region, access, and contractor. Ranges on this page are compiled from the sources on our methodology page. Get at least two local quotes.

Trunk-and-branch leaks: A spot repair on a main line might cost $150 to $2,000, but if the leak is under a finished floor, access alone can add $500 to $3,000. A reroute ($600 to $7,500) is often cheaper than opening the slab because you just redirect that branch over the ceiling.
Manifold leaks: Because each fixture has a dedicated line, a spot repair means opening the slab right at that line. Epoxy lining ($500 to $3,500 flat, or $80 to $250 per foot) becomes more attractive, but if many home runs are old, the per-foot cost multiplies quickly. A whole-home repipe ($1,500 to $15,000) might be smarter than fixing lines one by one.
Remote manifold leaks: These shorter lines reduce epoxy lining cost per line, but accessing multiple manifolds can complicate detection and may require multiple access points.

Use our Slab Leak Cost Calculator to estimate costs based on your layout and leak type.

What are the most common mistakes homeowners make about under-slab layouts?

Guessing your layout or jumping straight to a repair without mapping your pipes can turn a $1,000 fix into a $10,000 nightmare. Avoid these costly assumptions.

Assuming all leaks are in one spot: A trunk-and-branch leak can soak a large area of the slab, but the pipe break might be yards away. Don’t break concrete until you’ve used a professional detector like acoustic or thermal imaging.
Thinking a manifold means “just replace one line”: While manifold systems isolate fixtures, the dedicated lines could be clustered deep in the slab, making spot repair harder than you think. Epoxy may be a better trenchless option.
Skipping the water-meter test: Without it, you might call a plumber for a false alarm or miss a slow leak until it turns into a $5,000 tear-out. The 15-minute test confirms the leak first.
Digging before you know what’s below: Opening a slab without locating pipes can damage other lines or post-tension cables. Always call a licensed plumber for excavation.

Let the Repair Method Finder tool guide you to the least invasive fix.

How do layout options compare when choosing a repair method?

Your choice between spot repair, reroute, epoxy, or repipe hinges on which layout you have. Here’s how the most common designs stack up.

Trunk-and-branch: Rerouting is often cost-effective, especially when you can abandon a leaking branch and run a new PEX line above ground. Spot repair works for main-line leaks. Epoxy can coat the main if accessible.
Manifold: Epoxy lining suits the dedicated lines, but multiple lines increase total cost. A repipe may be cheaper than epoxying every home run. Rerouting is messy because of the number of lines.
Remote manifold: The shorter runs favor epoxy, but you might need to expose several manifolds, which adds labor.

Visit our Repipe Cost Calculator if you’re leaning toward a full replacement.

When can I map my under-slab layout myself, and when should I call a plumber?

Mapping your layout is 100% DIY-friendly, as long as you don’t open the slab. Use the water-meter test and a sketch pad. Call a licensed plumber the moment you confirm a leak or need to discuss repairs that involve breaking concrete.

You can: Run the meter test, draw your floor plan, locate the water heater and any manifold panels, and note where pipes stub up. All of this is free and safe.
A plumber must: Use leak detectors (acoustic, thermal, or radar) to pinpoint the exact spot, cut the slab, tunnel under it, or perform any rerouting or epoxy work. Never attempt to open a concrete slab yourself. The risk of hitting a post-tension cable or other utility is high, and it can cause structural damage or injury.
Get two quotes once you know your layout. A clear sketch helps the plumber see the job scope and keeps your estimate honest.

The Repair Method Finder can help you decide on the right pro fix after your mapping is done.

Row	Trunk-and-Branch	Manifold
Number of main lines under slab	Two (hot and cold)	One (cold only; hot water generated at manifold)
Branch lines	Several from the main	Dedicated home runs to each fixture
Leak isolation	Harder, one leak can affect multiple fixtures	Easier, each fixture has its own line
Rerouting	Simple, disconnect branch and run overhead	Complex, many separate lines; full repipe often better
Epoxy applicability	Good for main line; branches harder	Good for individual lines, but cost adds up per line
Cost per leak spot repair	$150-$2,000 plus access	$150-$2,000 per line, plus access for each spot

Questions this page answers

How deep are water lines under a concrete slab?

Water lines are typically buried 2-4 feet below the slab grade, inside the gravel sub-base and encased by the concrete. The depth can vary depending on local frost lines and building codes. Plumbers use specialized locators, not just a shovel, to find them. Estimate $150-$400 for professional detection, as of 2026. See [our methodology](/methodology/) for cost sources.

What does under-slab plumbing look like in a typical home?

In most homes built on a slab, you’ll find a trunk-and-branch layout: one hot and one cold main line running horizontally, with smaller lines branching up through the slab to sinks, showers, and appliances. The pipes are typically copper or, in newer homes, PEX. You can’t see them, but a floor plan can help you visualize the likely paths.

Can I get a diagram of my home’s under-slab plumbing?

Builders rarely provide as-built plumbing diagrams. You can create your own by sketching your floor plan and marking where pipes emerge. For a precise map, a leak detection company can use ground-penetrating radar or acoustic methods. Expect to pay $150-$400 for professional location, as of 2026. [Learn more on our methodology page](/methodology/).

Does insurance cover under-slab plumbing repairs?

Standard HO-3 policies typically cover slab leaks only when the leak results from a covered event, such as a burst caused by freezing, not ordinary wear and tear. Some policies may also cover access and restoration if the leak is sudden and accidental. Confirm with your carrier before authorizing any work.

How do I know if my home has a manifold plumbing system?

Check near your water heater for a plastic or metal panel with several knobs or levers, each labeled with a fixture name. This central manifold sends dedicated hot and cold lines to each fixture. If you see one, you have a manifold (or home-run) system. These are common in homes built after 2000.

What is the cheapest way to fix a leak under the slab given my layout?

For a trunk-and-branch system, spot repair is usually cheapest at $150-$2,000. But if the leak is under a finished floor, a reroute ($600-$7,500) may avoid costly floor restoration. For manifold systems, epoxy lining a single line ($500-$3,500) can be cheaper than opening the slab, but multiple lines add up. Always get two quotes.

How long do under-slab pipes last?

Copper pipes under a slab can last 50 years or more, but water chemistry and soil conditions can shorten that. Galvanized steel pipes last 20-50 years. If your home is over 40 years old and you’ve had one leak, your pipes may be reaching end of life. A whole-home repipe might be more cost-effective than repeated spot repairs.

Are under-slab pipes always in straight lines?

Not always. Pipes may be routed to avoid structural beams or other obstacles, so they can follow slight curves. However, they generally take the most direct path from the main to the fixture. Professional leak detectors expect some deviation, which is why they combine acoustic listening with floor-tracing tools.

Your under-slab plumbing layout isn’t a mystery you need to live with. By running the water-meter test, sketching your fixture points, and identifying whether you have a trunk, manifold, or remote manifold setup, you can steer your repair toward the most cost-effective method. Remember, a spot repair starts at $150, but a misdiagnosed layout can push you toward a $15,000 repipe. Use the Slab Leak Triage and Repair Method Finder to take control first.