Water Supply Rough-In: Layout, Spacing, and Stub-Out Heights

Why Rough-In Dimensions Matter

Rough-in work happens before walls are closed. Once drywall or tile goes up, stub-outs must land in exactly the right place for fixtures to connect without modification. An off-center supply to a lavatory faucet, a stub-out that sits too low for a tub spout, or a hot-and-cold pair that is too close together will force costly rework or force the installer to use flexible correctors that inspectors may reject. Getting it right the first time is a core professional skill and a direct requirement for journeyman licensing.

Reading Manufacturer Rough-In Sheets

Every fixture manufacturer publishes a rough-in dimension sheet for each model. These sheets show:

• AFF (above finished floor): the height at which the supply stub-out should emerge from the wall, measured to the centerline of the fitting
• Centerline offset: horizontal distance from a reference point (usually the centerline of the drain or the finished side wall) to the centerline of each supply
• Hot and cold spacing: the distance between hot and cold supply centerlines (commonly 8 inches on center for lavatories and kitchen sinks; tub/shower valves vary by valve model)
• Stub-out projection: how far the threaded or sweat fitting should protrude from the face of the rough framing

Always use the sheet for the exact model being installed. Dimensions differ between manufacturers and even between product lines from the same manufacturer. Before the lab begins, your reference card must be verified by the instructor — working from incorrect dimensions wastes material and time.

Common Rough-In Heights by Fixture

The following ranges reflect typical industry practice. Always confirm against the specific rough-in sheet and local code amendment:

• Water closet: Cold supply only; commonly 6–8 inches AFF to supply centerline, located to the left of the drain centerline (varies by model)
• Lavatory: Hot left, cold right; supplies commonly 20–22 inches AFF; 8 inches on center (4 inches each side of drain centerline) for most widespread faucets
• Tub/shower valve: Height and offset are valve-specific; the rough-in sheet for the valve body — not just the trim — governs; blocking in the stud wall is required to support the valve
• Kitchen sink: Hot left, cold right; commonly 18–22 inches AFF; 8 inches on center at the drain centerline or as specified

These are starting points. The rough-in sheet is the authority.

Layout Sequence in the Stud Wall

1. Snap a level chalk line at the AFF height for each fixture group. Use a laser level or spirit level; a sloped chalk line creates a sloped stub-out.

2. Mark the centerline of the drain or valve on the sole plate and transfer it plumb up the stud bay to the chalk line.

3. Mark hot and cold positions at the specified offset from centerline. Mark clearly: an H for hot (left when facing the wall), C for cold (right).

4. Drill through plates with a hole saw sized for the pipe plus sleeve. Keep holes centered in the plate thickness to preserve structural integrity and meet fire-blocking rules.

5. Install pipe hangers at the intervals required by the applicable code for the pipe material and size. For PEX-B and copper in most codes, horizontal support spacing is specified; vertical runs have their own interval. Never exceed the code maximum unsupported span.

6. Run pipe from the main lines to each stub-out location.

7. Install the drop-ear elbow or stub-out elbow at the chalk-line height, with the face of the fitting flush to or projecting the specified amount beyond the face of the rough framing. Screw the drop-ear ear into a solid blocking member, not just drywall backing.

8. Cap all openings immediately. Caps stay on until fixture connection.

9. Mark stub-out heights on the adjacent stud in permanent marker for the inspector and the finish plumber.

Pipe Support Requirements

The IPC and UPC both specify maximum hanger spacing by pipe material and diameter. For ½-inch copper and PEX in horizontal runs, consult the current edition of the applicable code for your jurisdiction. The key rule is simple: zero unsupported spans may exceed the code maximum. Undersupported pipe sags, stresses fittings, transmits vibration, and can fail at joints over time.

At plates, pipe must pass through holes or notches that are protected by nail plates (strike plates) when the edge of the hole is within the code-specified distance from the face of the framing member.

Safety in the Rough-In Lab

• Safety glasses are required at all times when drilling, cutting, or working overhead. Chips, sawdust, and copper shavings are eye hazards.
• Lockout/tagout (LOTO): In a live shop, confirm that any existing supply lines feeding the mock-up are isolated and de-energized before cutting in. Follow your shop's LOTO procedure.
• Drill safety: Use the correct bit for the material, keep cords clear of the drill path, and never reach around a spinning bit.
• Deburr cut copper immediately with a reamer or file. Copper burrs cause cuts and restrict crimp fittings from seating fully.
• PEX crimp: Inspect every crimp ring with the go/no-go gauge before moving on. An uncrimped ring will leak under pressure.
• Caps: Pressure-test caps must be rated for the test pressure. Confirm before pressurizing.

Self-Inspection Before the Instructor Check

Measure each stub-out height from finished floor level (the top of the subfloor in your mock-up, or the reference line marked by the instructor). Record the measured value and the specified value on your inspection sheet. Calculate the deviation. The pass criterion for this lab is all dimensions within ½ inch of specification. Correct any out-of-tolerance stub-outs before calling for the instructor check. Developing the habit of self-inspection before requesting approval is a professional expectation on every job site.