Pipe Sizing + Material Reference

Why this matters

Wrong pipe material = code violation, wrong size = poor flow + customer complaint. Each material has applications + limits + connection methods. The plumber who knows the differences cold installs the right system the first time. This is the field card.

Pipe materials overview

Copper sizing

Type K (thickest wall): underground service, durability priority.

Type L (medium wall): standard residential supply. Sweat-soldered, press-fitted, OR compression.

Type M (thinnest acceptable): light residential supply only; not for high-pressure.

DWV copper (thinnest, non-pressure): drainage in older homes.

Standard sizes (nominal inch):

• 1/2" (5/8" OD): kitchen, bath supply runs
• 3/4" (7/8" OD): main supply branches
• 1" (1-1/8" OD): main supply to house
• 1-1/4", 1-1/2", 2": commercial + main service

Flow rate (Type L):

• 1/2": ~ 5 GPM safe
• 3/4": ~ 11 GPM safe
• 1": ~ 20 GPM safe

PEX sizing

Color code:

• Red: hot
• Blue: cold
• White: combined OR neutral
• Yellow: gas (PEX-AL-PEX rare)

Brands:

• PEX-A (Uponor / Wirsbo): cross-linked + expansion-friendly; flexible
• PEX-B (Viega, Apollo, Watts): cross-linked but stiffer; crimp/clamp
• PEX-C: less common

Connection methods:

• Crimp (copper ring): pre-2000 standard; needs crimp tool
• Clamp (Oetiker stainless): cinch tool; reusable, easier inspection
• Expansion (PEX-A only): expand pipe + insert fitting; cold-weather seal
• Push-fit (SharkBite): no-tool; quick repair; expensive per fitting

Sizes: 1/4" - 1" residential common; same flow as 1 size up copper (smaller ID).

Limits: outdoor UV degradation; install must be protected from sunlight.

CPVC sizing

CTS (Copper Tube Sizing): 1/2", 3/4", 1" common.

Connection: solvent-weld with primer + CPVC cement (clear OR orange).

FlowGuard Gold: orange-colored common brand.

Use: cold water supply; some hot OK (rated to 180°F).

Limits: brittle in cold; UV-damaged; some areas restrict (check local code).

PVC sizing (DWV + irrigation)

Schedule 40 (white): pressure + DWV.

Schedule 80 (gray, thicker wall): higher pressure.

Standard DWV sizes: 1-1/4", 1-1/2", 2", 3", 4".

Connection: solvent-weld with PVC primer (purple OR clear) + PVC cement.

ABS sizing (DWV)

Black, slightly less brittle than PVC. Solvent-weld with ABS cement (no primer). Standard sizes match PVC.

Not interchangeable with PVC at solvent welds without transition cement.

Galvanized iron (legacy)

Threaded joints; thread paste OR PTFE tape.

Problem: corrosion narrows ID over decades (50% capacity loss common).

Service work: re-pipe to PEX OR copper rather than patch.

Black iron pipe (gas)

Threaded with pipe dope OR yellow gas-rated PTFE.

Sizes 1/2", 3/4", 1", 1-1/4"+: sized by demand + length per NFPA 54.

Cast iron (DWV in older homes)

Hub + spigot: oakum + lead-pour OR lead-and-oakum.

No-hub: neoprene gasket + stainless band clamp (modern; faster).

Cast iron service is quieter than PVC; some upscale new construction uses cast iron for DWV.

Pipe sizing rules of thumb

Supply sizing per fixture units + simultaneous demand: 1/2" branch 1 - 2 fixtures; 3/4" branch 3 - 5 fixtures; 1" main whole-house up to 6 - 8 fixtures simultaneous.

DWV per drainage fixture units (DFU): 1-1/4" branch 1 DFU (small lav); 1-1/2" 1 - 3 DFU; 2" 6 - 8 DFU; 3" 20 - 35 DFU (toilet + group); 4" main 60 - 200+ DFU.

Pipe support spacing

Copper: 6 ft horizontal, 10 ft vertical. PEX: 32" horizontal, 4 ft vertical. CPVC: 32" horizontal, 3 ft vertical (cold; 5 ft larger). PVC DWV: 4 ft horizontal, 10 ft vertical (at each floor). Cast iron: 5 - 10 ft horizontal, at each floor vertical.

Joining methods

Sweat solder: traditional copper joining. 95/5 solder + flux + heat. Strong, reliable, slow.

Press-fit (Apollo, Viega ProPress, NIBCO): copper jointed with stainless ring + ProPress tool. Fast, no flame. Premium tool cost .

Compression (brass): ferrule compresses around copper tubing. Reusable for service.

Crimp PEX: copper ring + crimp tool.

Cinch PEX: stainless clamp + cinch tool.

Expansion PEX-A: expander tool stretches pipe; fitting inserted; pipe shrinks back.

Solvent weld (CPVC, PVC, ABS): primer + cement; chemical bonding.

Threaded: NPT (National Pipe Tapered) for iron + brass. Pipe dope OR PTFE.

Common pipe material mistakes

Wrong material for application (PVC supply lines = code violation in most jurisdictions). Wrong cement (PVC cement on CPVC; ABS cement on PVC; won't bond). PEX in direct sunlight (UV degrades; install protected). Galvanized used new (long-term corrosion). Black iron for water (rusts inside).

Mixed metal connections (copper + galvanized): dielectric union required to prevent galvanic corrosion.

Common service scenarios

Failed galvanized supply line: repipe with PEX-A (fastest); whole-house 1 - 2 days work.

Slab leak (under concrete): re-route around slab with PEX OR copper.

Corroded copper from acidic water: install water softener + repipe affected section.

Frozen pipe burst: PEX more freeze-tolerant than copper; insulate + heat tape.

Truck stock by trade

Plumbing: copper assortment (1/2", 3/4", 1"), PEX (1/2" + 3/4" red + blue), CPVC (1/2" + 3/4"), PVC fittings DWV, brass compression fittings, solder + flux + cleaner.

HVAC: copper (1/2", 5/8", 7/8") for refrigerant lines, soft + hard copper depending on application.

Insulation

Pipe insulation (foam) on hot water supply for efficiency + freeze protection on cold lines in exterior walls. R-3 to R-6 typical.

References

• IPC Chapter 6 (Water Supply)
• IRC Chapter 29 (Plumbing Materials)
• ASTM F876, F877 (PEX standards)
• ASTM B42 (Copper pipe standards)
• ASTM D1785 (PVC pipe), D2846 (CPVC)
• Manuall internal: Water Pressure + Flow, Soldering + Brazing