2021 IRC Chapters 25 and 26
Before any of the material in this course matters, the rough-in has to survive the ground rules that apply to every plumbing job: a permit before the work starts, an inspection before it gets covered, a test that proves the system tight, and protection from the everyday hazards of a framed house, a trench, and a slab. GCHS staff are not the ones pulling the permit or holding the test gauge, since the actual plumbing is done by licensed plumbers, but an inspector, an estimator, or a construction manager who does not know these baseline rules cannot catch the rough-in mistakes that get expensive once the walls close up. This lesson covers Chapters 25 and 26 of the 2021 IRC (Part VII, Plumbing): administration and testing, then protection, trenching, and support of piping.
Plumbing work generally requires a permit before it begins, issued by the local building department. The IRC exempts a short list of small maintenance items: stopping a leak in an existing pipe, valve, or fixture; clearing a stoppage; and removing and reinstalling a water closet, as long as that work does not involve replacing or rearranging any pipe, valve, or fixture. The moment a concealed pipe or trap has to be replaced, or new equipment such as a water heater is installed, that is new work and needs a permit and inspection like anything else. This distinction matters constantly in rehab: a property manager who swaps a failed water heater for one of the same size and fuel type has still touched fuel or electrical connections, the relief valve and its discharge piping, venting, and often a pan, and that is not maintenance.
The single rule that shapes every plumbing inspection is that a plumbing or drainage system, or any part of it, may not be covered, concealed, or put into use until it has been tested, inspected, and approved by the building official (P2503.2). Drywall, insulation, fireproofing, and backfill all count as covering. Concealment is not only drywall. An insulation contractor who fills exterior wall cavities over a water line before the rough-in inspection has concealed that work just as effectively, and the correct response is to require it uncovered, not to accept the plumber's description of what is underneath. Inspections generally follow the order in which work would otherwise be concealed: underground and under-slab piping is inspected before the pour, rough-in piping is inspected before drywall, and the final inspection looks at the finished, working system: fixtures set and connected, traps filled with water, each fixture filled and drained to prove its traps and connections watertight, and, where the local authority requires it, a smoke or peppermint test for gastightness (P2503.5.2). The pressure and water tests of the piping itself belong to the earlier concealed stages. The building official may approve a portion of the work as completed (R109.1), such as an under-slab section, and allow it to be covered so the rest of the job can proceed; what is never allowed is covering work that has not yet been inspected at all.
Before it is concealed, the drain-waste-vent (DWV) system has to prove itself tight (P2503.5.1). The code allows three test methods, chosen by piping material. The water test fills each section with water to a point not less than 10 feet above the highest fitting connection in that section, or to the highest point of the completed system, and holds it for 15 minutes; the section must prove leak free by visual inspection. A handout or online summary that quotes a 5-foot head does not match the 2021 text and should not be used for 2021 work. For piping other than plastic, the code also allows an air test: hold a gauge pressure of 5 psi, or a 10-inch mercury column, for 15 minutes without adding more air. Plastic DWV piping is not air tested; it gets the water test or a vacuum test, which evacuates the section to negative 5 psi (or a negative 10-inch mercury column) and holds it for 15 minutes without removing more air. Compressed air stores energy, so a failing plastic joint under air pressure can come apart violently, while a failed water test simply drips. The building sewer is tested separately (P2503.4): a test plug goes in at the connection to the public sewer, and the sewer is filled and pressurized to not less than a 10-foot head of water with no drop in pressure for at least 15 minutes.
The water distribution system gets its own test before concealment (P2503.7): the completed system or section is tested with water at not less than the working pressure of the system, or, for piping other than plastic, by an air test at not less than 50 psi, and held for at least 15 minutes, proved tight. For PEX, testing with compressed gas is allowed as an alternative only where the manufacturer's instructions specifically authorize it and no other rule prohibits it. The point of holding any of these tests for a period of time, rather than bringing the system to pressure and reading it once, is that a pinhole or an under-tightened joint can take several minutes to show itself as a slow weep. A momentary reading can hide exactly the leak the test exists to catch. If a test fails at one joint, the section has to be tested again and hold for the full period after the repair; spot-checking only the one fitting that was fixed does not show that the rest is tight, because working on one joint can disturb others nearby.
In the field
A common rough-in problem GCHS inspectors catch in older infill and rehab work is a PEX supply line stapled through studs with less than an inch of wood between the tubing and the face of the stud. At that cover, an ordinary drywall screw driven later reaches the tubing, and the pinhole leak it causes does not show up until the wall is finished and someone notices a damp baseboard months later. The fix at rough-in is a steel shield plate over the framing member, not a note to "be careful with screws," because nobody hanging drywall knows where that line runs.
Section P2603 covers the everyday hazards a finished pipe run faces before it is ever put into service. In concealed locations, where piping other than cast iron or galvanized steel runs through holes or notches in studs, joists, rafters, or similar members and sits less than 1-1/4 inches from the nearest edge of that member, it must be protected by a steel shield plate, minimum thickness 0.0575 inch (No. 16 gage), covering the pipe where the member is notched or bored and extending at least 2 inches above sole plates and below top plates to catch a fastener driven at an angle (P2603.2.1). This is one of the most common corrections found at rough-in: a drain or supply line notched or bored tight to the face of a stud with no plate over it. Section P2603.2 also limits drilling and notching of wood-framed structural members to what R502.8, R602.6, R802.7 and R802.7.1 allow. In joists, for example, R502.8.1 keeps notches out of the middle third of the span and limits them to one-sixth of the member depth. A shield plate answers a fastener hazard, it does not answer a structural one, so a notch cut beyond what those sections allow has to be corrected by rerouting or reframing, not by adding a plate. Two more P2603 rules matter in rehab. Metallic piping other than cast iron, ductile iron, and galvanized steel may not touch steel framing, concrete, masonry, or corrosive soil directly; where plastic sheathing is used to separate them, it must be at least 0.008 inch (8 mil) thick and must let the pipe move (P2603.3). And a pipe that passes through a foundation wall needs a relieving arch, or a pipe sleeve built into the wall that is two pipe sizes larger than the pipe (P2603.4), so the wall never bears on the pipe. Where the pipe also passes through the envelope, the annular space is sealed with caulking, foam, or a gasket (P2606.1).
In localities where the winter design temperature in Table R301.2 is 32 degrees Fahrenheit or lower, a water, soil, or waste pipe may not be installed outside the building, in exterior walls, in attics or crawl spaces, or anywhere else subject to freezing unless it is protected by insulation, heat, or both (P2603.5). Water service pipe must be installed at least 12 inches deep and at least 6 inches below the frost line, whichever requirement is deeper; in a jurisdiction with an 18-inch frost line, that works out to 24 inches, not the flat 12-inch minimum. Outdoor hose bibbs get their own rule in P2903.10: a hose bibb subject to freezing, including the frostproof type, needs an accessible stop-and-waste valve inside the building so it can be shut off and drained in cold weather. The exception is a frostproof bibb installed so that its stem extends through the wall insulation into an open heated or semiconditioned space. Even then, a hose left attached traps water in the barrel, and the pipe can split inside the wall where nobody sees it until spring.
Where the bottom of a trench forms the bed for the pipe, the pipe needs solid, continuous bearing between joints, never rocks or blocks, because point support lets the pipe sag and deflect between the supports (P2604.1). Where the trench is over-excavated, it is brought back to grade with compacted earth, sand, fine gravel, or similar granular material, and rocky or unstable soil is over-excavated by two or more pipe diameters and rebuilt with compacted granular material. Backfill must be free of construction debris, and free of rocks, broken concrete, and frozen chunks until the pipe is covered by at least 12 inches of tamped earth. It is placed evenly on both sides of the pipe and tamped to keep alignment, and loose earth goes in 6-inch layers, each tamped (P2604.3). That protects plastic pipe from being dented or punctured and keeps the trench from settling out from under the pipe later. Where a trench runs parallel to a footing or wall, it may not extend into the bearing plane of that footing or wall, which starts at the outside bottom edge and slopes downward at 45 degrees from horizontal (P2604.4); the pipe must never become what is holding up the structure.
Every pipe material has a maximum horizontal hanger spacing in Table P2605.1, and the spacing tracks how stiff the material is: PEX 1 inch and smaller, the most flexible common material, gets the tightest spacing at 32 inches, CPVC 1 inch and smaller needs support every 3 feet, PVC and ABS drainage piping every 4 feet, cast iron every 5 feet (10 feet where 10-foot lengths are installed), copper tubing 1-1/4 inches and smaller every 6 feet, and steel pipe, the stiffest of the group, every 12 feet. Getting this wrong does not usually cause an immediate failure; it shows up later as a belly in a drain line, a low spot between widely spaced hangers where water and solids collect and the line clogs repeatedly, a maintenance problem the homeowner lives with for years after the framing is long closed up. Hangers and anchors also have to carry their share of the weight of the pipe and its contents, be wide enough not to distort the pipe, and be made of an approved material that will not promote galvanic action (P2605.1); a bare steel strap on copper tubing sets up galvanic corrosion at exactly the point meant to hold the pipe up.
This course teaches the plumbing provisions of the 2021 IRC because that is the reference edition GCHS uses for training and because many jurisdictions build their local amendments from an IRC or IPC base. In practice, though, Texas law lets individual cities choose their own plumbing code and adopt local amendments on top of it, and many Texas cities adopt the International Plumbing Code or the Uniform Plumbing Code rather than the IRC's plumbing chapters directly. GCHS staff always confirm the specific code and amendments adopted by the jurisdiction where a project sits rather than assuming the IRC chapters in this course apply verbatim. Regardless of which code a city has adopted, the actual plumbing work has to be performed by a plumber licensed by the Texas State Board of Plumbing Examiners, which is the licensing authority for plumbing work statewide.
A worked example on the test numbers: a two-story house has its highest DWV fitting connection 9 feet above the basement floor drain being tested. Under the 2021 IRC water test, the section must be filled to at least 10 feet above that highest fitting connection, meaning the test riser has to reach roughly 19 feet above the floor drain, not simply to the highest fitting itself. As a rough pressure equivalent, each foot of water head is about 0.433 psi, so a 10-foot head works out to about 4.3 psi, which is in the same range as the 5 psi air test the code allows for non-plastic piping.
1. Under the 2021 IRC, a DWV section being water-tested must be filled to at least what level above the highest fitting connection in that section?
2. An inspector reviewing a training handout finds a DWV water test head of 5 feet listed. Which conclusion fits the 2021 IRC?
3. When a DWV system of piping other than plastic is tested with air instead of water, the required pressure and hold time are:
4. An inspector arrives at a rough-in and finds that a plumbing subcontractor has already applied fireproofing over a section of DWV piping before it was tested. The correct response is to:
5. Which of the following is normally exempt from a plumbing permit under the IRC?
6. A property manager replaces a failed water heater with a new unit of the same size and fuel type. This work:
7. An inspector finds a PEX water line stapled through studs with about 1 inch of wood between the tubing and the face of the stud. The code requires:
8. The steel shield plate protecting piping at a bored or notched framing member must be at least what thickness?
9. An inspector finds a 2-inch drain installed through a deep notch cut in the bottom edge of a floor joist near the middle of its span, with no shield plate added. The correct response is to:
10. In a locality where the winter design temperature is at or below freezing and the established frost line is 18 inches, the minimum burial depth for a water service pipe is:
11. An inspector finds a PVC drain hung at roughly 8-foot intervals instead of the required spacing. The most likely practical consequence is:
12. Threaded steel water pipe run horizontally may be supported at intervals up to:
13. A trench is being dug parallel to an existing footing. Under P2604.4, the trench may not extend into:
14. Which of the following best describes how Texas handles the residential plumbing code?