5.2 Joints, Connections, and Dissimilar Materials in Water Piping

Prohibited joints and connections — IPC 605.9

Start with the list of what you may never do, because exam items are often phrased as "which of the following is prohibited."

The following joints and connections shall be prohibited in the water supply system:

1. Cement or concrete joints.
2. Mastic or hot-pour bituminous joints.
3. Joints made with fittings not approved for the specific installation.
4. Solvent-cement joints between different types of plastic pipe, except as provided in 605.23.2.
5. Saddle-type fittings.

Compare the parallel drainage list in IPC 707.1, which adds "joints between different diameter pipes made with elastomeric rolling O-rings" and also bans saddle-type fittings. Saddle fittings are prohibited on both the supply and the drainage side.

Joining methods by material

Two rules easy to forget:

• IPC 605.5.1 Mechanically formed tee fittings — a collared branch outlet formed in copper tube with an approved tool is permitted, but the joint shall be brazed. A soldered mechanically formed tee is not code compliant.
• IPC 605.8 Manufactured pipe nipples must conform to Table 605.8 (ASTM A733 for steel, ASTM B687 for brass).

Dissimilar materials — IPC 605.23

Galvanic corrosion is the reason. When two metals with different electrode potentials touch in the presence of an electrolyte (water), the less noble metal corrodes.

The practical corollary: copper male adapter screwed directly into a galvanized fitting is a defect waiting to happen, and it fails 605.23.1 on its face.

The same principle appears in IPC 305.1 (metallic piping other than cast iron, ductile iron and galvanized steel may not contact steel framing, concrete or masonry) and IPC 308.3 (hangers and strapping of approved material that will not promote galvanic action). A copper line hung in a bare steel strap through a steel stud assembly violates all three ideas at once.

Solder, flux and lead

Three numbers, three contexts:

Fixture supplies and connectors

IPC 604.5 sets the minimum fixture supply size from Table 604.5 and adds three installation rules:

• The fixture supply pipe shall terminate not more than 30 inches from the point of connection to the fixture.
• A reduced-size flexible water connector between the supply pipe and the fixture shall be of an approved type.
• The supply pipe shall extend to the floor or wall adjacent to the fixture.

Table 604.5 minimum fixture supply sizes worth memorizing:

Footnote a permits one nominal tube size smaller for an individual distribution line from a manifold in a parallel water distribution system, where the developed length of the distribution line is 50 feet or less and available pressure at the meter is 35 psi or greater.

IPC 604.10 governs gridded and parallel manifolds. Manifolds are sized by Table 604.10.1 on total demand in gpm, at 4 feet per second (cold-water-only style installations) or 8 feet per second:

604.10.2 requires individual fixture shutoff valves at the manifold to be identified as to the fixture supplied, and 604.10.3 requires access to manifolds with integral valves.

Installation details that get cited

• IPC 604.2 System interconnection: at points of interconnection between hot and cold piping and individual fixtures, appliances or devices, provisions must prevent flow between the two systems. A failed single-lever cartridge that lets hot into the cold line violates this.
• IPC 604.11: individual pressure balancing in-line valves for individual fixture fittings comply with ASSE 1066, must be installed with access, and shall not be used alone as a substitute for the ASSE 1016 shower valve required by 412.3.
• IPC 608.10 Reutilization prohibited: water that has been used for cooling equipment or other processes shall not be returned to the potable water system; it may be reused for flushing water closets and urinals or for irrigation, provided it is not sprayed onto areas open to public use.

Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(cc) deletes the exception in IPC 605.15.2, and Rule 1.2(E)(1)(jj) deletes the exception in IPC 705.10.2 — the exceptions that otherwise allow one-step cements without primer on certain plastic joints. In Colorado, primer is not optional on those joints.