Running plumbing through walls and floors looks deceptively simple. Drill a hole, push the pipe through, congratulate yourself, and go find lunch. Unfortunately, houses have a habit of objecting when you casually remove important pieces of their framing.
A good plumbing rough-in has to satisfy several competing demands at once. The pipe must reach the fixture efficiently, structural framing must remain strong, drain lines must maintain the correct slope, supply tubing needs room for movement, and concealed pipes must be protected from the future homeowner who decides that a three-inch drywall screw is the perfect tool for hanging a picture.
This guide explains how to run pipes through walls and floors safely and efficiently, including how to plan plumbing routes, drill studs and floor joists, install PEX, copper, CPVC, and DWV piping, protect pipes from damage, and avoid the mistakes that turn a Saturday project into an expensive call to a plumber or structural engineer.
Important: Building and plumbing requirements vary by jurisdiction. The dimensional limits discussed below reflect common U.S. residential-code principles, including current International Residential Code guidance, but your locally adopted code and the framing or piping manufacturer’s instructions always take priority.
Plan the Plumbing Route Before Drilling Anything
The best hole is often the one you discover you do not need to drill.
Before reaching for an auger bit, identify where the pipe begins, where it ends, and what obstacles sit between those two points. Locate studs, joists, beams, headers, electrical wiring, HVAC ducts, existing plumbing, blocking, fire stops, and load-bearing walls.
A modern electronic stud finder that can detect metal or energized wiring can help, although exploratory openings are sometimes necessary during major remodeling. When cutting drywall, keep the blade shallow until you know what is hiding behind the surface. This Old House and Home Depot both emphasize locating framing and concealed utilities before drilling or opening walls.
Think Differently About Supply and Drain Pipes
Water-supply lines and drain-waste-vent piping behave very differently.
PEX tubing is flexible enough to make sweeping turns and can often run continuously through several framing cavities with fewer fittings. Copper and CPVC are more rigid and usually require more precise alignment. PVC or ABS drain piping is even less forgiving because horizontal drainage must maintain a continuous slope toward the drain.
In other words, a supply line can sometimes detour around an obstacle. A gravity drain cannot climb over one and then politely resume draining.
Know What Kind of Framing You Are Drilling
Never assume every piece of wood behind drywall follows the same drilling rules. A standard wall stud, dimensional-lumber floor joist, engineered I-joist, LVL beam, header, and floor truss are structurally different products.
Before drilling, identify the member.
Drilling Holes Through Wall Studs
For conventional wood studs, centered holes are generally the safest approach because they leave the most wood between the pipe and either face of the wall.
Under the 2024 IRC provisions for conventional wood framing, bored holes in studs may generally be up to 60 percent of the stud depth, provided the edge of the hole remains at least 5/8 inch from the stud edge and the hole does not occur in the same section as a notch. In exterior or bearing walls, holes exceeding 40 percent require additional conditions such as doubled studs, with limits on consecutive doubled-and-bored studs.
Notches are more restrictive. A stud in an exterior or bearing wall generally cannot be notched deeper than 25 percent of its depth, while a stud in a nonbearing partition can generally be notched up to 40 percent.
Translation: drilling a properly located hole is usually much better than carving a miniature Grand Canyon into the side of a stud.
Be Careful With Top and Bottom Plates
Pipes commonly travel vertically between floors by passing through wall plates. That is normal, but large openings in load-bearing wall plates can require reinforcement.
For example, current IRC provisions address situations in which piping or ductwork removes more than 50 percent of the width of a top plate in an exterior or interior load-bearing wall. Depending on the assembly, a specified metal tie or another approved structural solution may be required.
If your drain requires a hole so large that the remaining plate looks nervous, stop and verify the framing requirement before continuing.
How to Run Pipes Through Floor Joists
Floor joists require even more attention because they carry floors, furniture, people, appliances, and occasionally that gigantic aquarium someone swore was a reasonable purchase.
Rules for Solid-Sawn Lumber Joists
For conventional dimensional-lumber joists, holes should generally be located toward the vertical center of the joist rather than near its top or bottom edges.
IRC guidance for sawn-lumber floor framing limits bored-hole diameter to no more than one-third of the joist depth. A hole must also remain at least 2 inches from the top or bottom of the joist and at least 2 inches from another hole or notch.
Notches have different limits. In general, notches are prohibited in the middle third of a joist span, while allowable end and outer-span notches are restricted in depth and size.
This distinction matters. A 2-inch hole through the correct part of a joist may be completely acceptable, while a 2-inch notch in the wrong place can seriously weaken the member.
Never Guess With Engineered I-Joists
I-joists look like oversized wooden I-beams, with engineered flanges at the top and bottom connected by a relatively thin web. They are designed to accommodate mechanical penetrations, but only in approved locations and sizes.
Do not apply ordinary dimensional-lumber rules to an I-joist.
Manufacturers such as Weyerhaeuser publish detailed hole charts showing where plumbing, electrical, and HVAC openings may be placed. The top and bottom flanges should not be cut or notched. Larger web holes are typically restricted based on their distance from bearings and the specific joist series, depth, span, and loading.
APA likewise recommends following the I-joist manufacturer’s hole requirements instead of improvising in the field.
If there is a manufacturer’s stamp on the joist, use it to identify the product and obtain the correct hole chart. Five minutes of research is considerably cheaper than discovering that your plumbing project now includes structural engineering.
Choose the Right Hole Size
The hole should be large enough for installation and normal pipe movement but not dramatically larger than necessary.
For rigid pipe, a slightly oversized hole makes alignment easier and prevents the pipe from grinding against the framing. Flexible tubing may also need a sleeve, isolator, or bushing where it passes through abrasive materials such as metal framing.
PEX manufacturers specifically caution against passing tubing through metal studs or concrete without appropriate protection. Manufacturer instructions also warn against supports or edges that can cut, pinch, or abrade the tubing.
Use the Correct Drill
For smaller supply pipes, a quality spade bit or self-feed bit may work. For larger plumbing penetrations, plumbers often use self-feed bits, auger bits, or hole saws.
Keep the drill square to the framing. An angled hole occupies more framing area, complicates pipe installation, and can reduce the amount of wood left near the wall surface.
When drilling several studs for a horizontal run, mark a consistent height using a level or laser. A straight row of holes makes rigid pipe installation dramatically easier.
Protect Concealed Pipes From Nails and Screws
One of the smallest plumbing accessories can prevent one of the most annoying plumbing disasters: the nail plate.
When a concealed pipe runs too close to the face of a stud, joist, rafter, or similar framing member, steel protection plates are used so future nails and screws cannot easily penetrate the pipe.
The 2024 IRC requires protection for many concealed pipes where the pipe is less than 1 1/4 inches from the nearest framing edge.
Stud guards and protection plates are specifically designed for this job and are widely used where plumbing passes through framing.
Install them before drywall goes up. The person hanging a cabinet ten years from now will never know you saved their kitchen from becoming an indoor water feature.
Running PEX Through Walls and Floors
PEX is particularly convenient for concealed residential supply runs because long coils allow tubing to snake through walls and floor systems with relatively few joints.
Fewer concealed fittings are usually desirable because every fitting represents another connection that must be made correctly.
Do not bend tubing tighter than the manufacturer’s minimum bend radius. Bend supports can be used for controlled 90-degree changes without inserting an unnecessary elbow in some applications.
Support spacing is product- and code-dependent. For example, SharkBite’s PEX installation guidance recommends support at regular intervals and enough freedom for normal thermal expansion and contraction, while Uponor publishes its own support requirements for its PEX systems. Always use the instructions for the exact tubing installed.
Avoid sharp hangers, excessive tension, direct flame, and unapproved exposure to heat or ultraviolet light. Pressure-test the completed system before closing the walls.
Running Copper and CPVC Through Framing
Rigid piping rewards accurate measurement. Unlike PEX, copper will not cheerfully curve six inches to compensate because your fifth hole wandered slightly to the left.
Lay out the entire run before drilling multiple studs. Use pipe supports or isolators where appropriate to reduce abrasion, movement, and noise.
Copper piping may expand, contract, and transmit sound through framing, so avoid wedging it tightly into undersized holes. Compatible isolating supports can reduce noise transfer while allowing controlled movement. Sioux Chief, for example, manufactures supports and isolators intended for copper, PEX, and CPVC installations.
If soldering copper, keep open flames away from combustible framing and follow appropriate fire-safety practices. Many remodeling situations allow joints to be assembled away from framing or made with an approved alternative connection system.
Running Drain, Waste, and Vent Pipe Through Walls and Floors
DWV piping is where planning becomes especially important because drain pipe is relatively large and gravity is an uncompromising building inspector.
Maintain the Required Drain Slope
Horizontal drainage piping cannot simply be installed level.
Under the 2024 IRC, horizontal drainage pipe 2 1/2 inches in diameter or smaller generally requires a minimum slope of 1/4 inch per foot. Pipe 3 inches or larger generally requires at least 1/8 inch per foot under the cited residential provision. Local amendments and specific system conditions can change requirements, so verify the applicable code.
Suppose a 2-inch sink drain travels 8 feet horizontally. At 1/4 inch per foot, it needs about 2 inches of total fall.
That matters when drilling consecutive joists or studs. The first hole and last hole cannot automatically be at identical elevations.
Use Drainage Fittings Designed for Flow
Drain fittings are shaped to guide wastewater and solids smoothly. Proper combinations of wyes, sanitary tees, sweeps, and bends depend on whether flow is changing from horizontal to vertical, vertical to horizontal, or horizontal to horizontal.
Current IRC drainage provisions require approved drainage fittings and uniform alignment and prohibit arrangements that create unnecessary obstructions to flow.
A pressure-pipe elbow may look similar to a drainage fitting from six feet away. Your wastewater, however, can apparently tell the difference.
Support Pipes Properly
Pipes should not simply hang between holes like laundry on a clothesline.
Proper supports maintain alignment, reduce vibration, protect fittings, and keep drainage piping at its intended slope. Support requirements vary according to piping material, diameter, orientation, and local code.
Manufacturers publish detailed support tables. Charlotte Pipe, for instance, provides specific horizontal and vertical support guidance for ABS, PVC, and CPVC systems, while PEX manufacturers provide their own spacing requirements.
Plastic piping also expands and contracts with temperature changes. Long runs should therefore be installed with the manufacturer’s expansion recommendations in mind rather than being rigidly trapped between framing members.
Seal Penetrations Where Required
Drilling through walls and floors can affect more than structure. Penetrations may also pass through fireblocking, smoke-resistant construction, sound assemblies, air barriers, or rated walls and floors.
Residential codes require fireblocking at specified concealed spaces and around certain penetrations. Rated assemblies require approved penetration systems capable of maintaining the required rating.
Do not assume that a heroic blob of whatever foam happened to be in the garage is an approved firestop system.
A Practical Step-by-Step Installation Process
1. Identify the Plumbing System
Determine the pipe material, diameter, fixture requirements, drain slope, connection type, and applicable manufacturer’s instructions.
2. Map the Entire Route
Mark the fixture locations and trace the proposed path through wall and floor cavities. Identify load-bearing framing and engineered structural members.
3. Locate Existing Utilities
Check both sides of the wall or floor where possible. Locate wiring, gas piping, HVAC equipment, and existing plumbing before drilling.
4. Mark Every Penetration
Use a level or laser for supply runs. For drain piping, calculate the required fall and mark each penetration accordingly.
5. Verify Structural Limits
Confirm the allowable hole size and location for every stud, joist, beam, truss, or engineered member. Never assume yesterday’s rule applies to today’s framing product.
6. Drill Carefully
Choose the smallest practical hole and keep the bit perpendicular to the framing. Stop if you encounter unexpected resistance that could indicate metal protection plates or concealed utilities.
7. Feed and Support the Pipe
Install sleeves, bushings, brackets, isolators, and straps appropriate for the piping system. Avoid forcing rigid pipe through badly aligned holes.
8. Add Protection Plates
Where piping lacks adequate setback from the framing face, install approved steel nail plates before wall or ceiling finishes are installed.
9. Complete Connections and Test
Pressure-test supply piping and leak-test or otherwise inspect drainage systems as required before concealing the work. Manufacturer guidance for PEX systems specifically calls for testing after installation.
10. Photograph the Rough-In
Before drywall goes up, photograph every wall and floor cavity. Include a tape measure in important photos so pipe locations can be estimated later.
Years from now, those photographs may be worth considerably more than the 30 seconds required to take them.
Common Mistakes to Avoid
- Drilling before identifying whether a wall is load-bearing.
- Using dimensional-lumber rules on engineered I-joists.
- Cutting or notching I-joist flanges.
- Drilling oversized holes merely because a larger bit is already in the drill.
- Installing DWV piping without calculating slope first.
- Running pipes close to drywall without nail plates.
- Forcing PEX into bends tighter than the manufacturer’s limit.
- Leaving rigid pipe unsupported between framing cavities.
- Creating unnecessary concealed fittings.
- Closing walls before pressure-testing or inspecting joints.
- Ignoring fireblocking or rated penetrations.
- Assuming a beam can be drilled simply because a joist can.
Field Experience: Lessons That Make Pipe Routing Easier
One of the most useful lessons in residential plumbing is that successful pipe routing usually happens before the drill starts spinning.
Imagine adding a second-floor bathroom above an existing kitchen. At first glance, the easiest route for the new sink drain appears to be straight across several floor joists and into an existing stack. The temptation is to mark a level line, drill five holes, and start feeding pipe.
Then you remember that the drain needs slope.
An 8-foot run of smaller horizontal drainage pipe at 1/4 inch per foot needs roughly 2 inches of fall. Suddenly, the final hole is substantially lower than the first. If the joists are shallow, the route that looked perfect on paper may violate allowable hole-clearance requirements before reaching the stack.
The better solution may be to move the branch closer to the stack, change fixture positioning, run part of the drain within a plumbing wall, or create a properly designed chase. Planning saves the framing from becoming Swiss cheese.
Supply lines offer another useful example. Suppose hot and cold water must cross a basement ceiling before rising into a bathroom wall. With rigid copper, every joist hole needs reasonably good alignment. A slightly crooked series of holes can require extra fittings or put unwanted stress on the tubing.
PEX changes the equation. Because flexible tubing can sweep gently between penetrations, the installation may use long continuous runs and fewer fittings. However, flexibility should not become an excuse for sloppy work. Tubing still needs proper supports, protection from sharp edges, suitable bend radii, and nail plates where it passes too close to framing surfaces.
Another lesson appears during remodels. You open a wall expecting empty stud bays and discover electrical cables, blocking, an HVAC chase, an old abandoned copper line, and something mysterious that no one is willing to identify.
Do not automatically drill through everything in a straight line.
Often the safest route moves vertically into a basement or crawlspace, travels horizontally through a more accessible area, and then rises again near the fixture. The path may use several extra feet of pipe but require fewer structural penetrations and provide better access for future repairs.
Noise deserves attention too. Pipes that fit tightly against framing can click, tick, squeak, or knock as water temperature changes and the pipe expands or contracts. Plastic isolators, compatible supports, sensible hole sizing, and proper fastening can make the finished plumbing much quieter.
Finally, experienced installers learn to think about the person who comes next. The plumber is not the final person who will touch the wall. Drywall installers, cabinet installers, trim carpenters, electricians, and future homeowners may eventually drive screws into it.
That is why nail plates matter. It is why rough-in photographs matter. It is why testing before closing the wall matters.
A beautiful concealed plumbing installation is invisible when the project is complete. Nobody walks into the finished bathroom and says, “Wow, look at that wonderfully centered 7/8-inch hole behind the drywall.” But ten years later, when nothing leaks, rattles, sags, or gets punctured by a screw, that invisible workmanship is doing exactly what it was supposed to do.
Conclusion
Learning how to run pipes through walls and floors is less about drilling holes and more about understanding what you are allowed to drill, where the pipe needs to travel, and how that pipe will behave after the wall is closed.
Plan the plumbing route first. Keep penetrations within structural limits. Follow manufacturer-specific instructions for engineered framing and piping products. Maintain proper DWV slope. Protect pipes near framing surfaces with nail plates. Support tubing correctly, seal required penetrations, and test everything before covering it.
Those habits may add a little time during rough-in, but they prevent structural damage, hidden leaks, noisy plumbing, and the particularly memorable experience of putting a screw directly through a water line.
Note: This article provides general residential plumbing and framing guidance based on current U.S. code principles and installation information from sources including ICC, APA – The Engineered Wood Association, Weyerhaeuser, Uponor, SharkBite, Charlotte Pipe, Copper Development Association, Sioux Chief, Oatey, This Old House, Family Handyman, The Home Depot, and Lowe’s. Local codes, approved plans, structural engineering requirements, and individual product instructions should always be verified before construction.
