Pipe Support Spacing by Material

Why this matters

Hangers are the part of a rough-in nobody budgets time for and every inspector looks at. Too few and a PVC drain sags out of grade between joists, a PEX hot line droops into a belly that holds air, a cast iron run settles at a coupling until it weeps. The spacing is a table, it changes by material and by size inside a material, and the two model codes do not print the same table. This card gives the IPC spacing as a field card, notes where the UPC and the pipe maker change it, and counts the hangers on a basement job.

The spacing card

From IPC 2021 Table 308.5, as adopted by your jurisdiction. Maximum spacing between supports; closer is always allowed.

 SUPPORT SPACING - IPC 2021 Table 308.5, as adopted
 --------------------------------------------------
 MATERIAL               HORIZONTAL   VERTICAL
 PVC pipe               4 ft         10 ft (g)
 ABS pipe               4 ft         10 ft (g)
 CPVC, 1 in and under   3 ft         10 ft (g)
 CPVC, 1-1/4 and over   4 ft         10 ft (g)
 PEX, 1 in and under    32 in        10 ft (g)
 Copper tubing,         6 ft         10 ft
   1-1/4 in and under
 Copper tubing,         10 ft        10 ft
   1-1/2 in and over
 Cast iron pipe         5 ft (c)     15 ft
 Steel pipe             12 ft        15 ft
 --------------------------------------------------
 (g) mid-story guide on 2 in and smaller
 (c) 10 ft where 10 ft lengths are installed

Read the size split inside a material. Copper and CPVC each have two rows. A 1-1/4 in copper line is 6 ft; a 1-1/2 in line is 10 ft. A 1 in CPVC line is 3 ft; 1-1/4 in is 4 ft.

Read both footnotes. The mid-story guide on plastic and PEX risers 2 in and smaller is a lateral guide halfway up a story, not just a support at each floor. The cast iron footnote lets horizontal spacing go to 10 ft only where 10 ft pipe lengths are used, so there is a coupling at each support rather than one unsupported coupling mid-span.

Where the UPC and the maker change it

UPC 2021 Table 313.3, as adopted, is a different table. It agrees with the IPC on several common rows (plastic DWV at 4 ft horizontal, small CPVC at 3 ft, small PEX at 32 in) and differs on others. The difference most likely to matter on a residential job is copper: as read, the UPC keeps 6 ft horizontal spacing up through 1-1/2 in tubing and goes to 10 ft at 2 in, where the IPC goes to 10 ft at 1-1/2 in. The UPC also states cast iron support in terms of joints (supports at or near the joints, at every joint where the pipe length exceeds a stated figure) rather than as a single distance. Read the row for your material and size in the edition on the job file.

The pipe maker can require closer. The maker's installation instructions are part of the listing. PEX makers commonly publish their own spacing, and some allow wider spacing when the tubing rides in a continuous support channel; CPVC makers publish spacing that tightens for hot water lines and higher temperatures. Where the maker's spacing is closer than the code's, the maker's governs; where a channel lets the maker allow wider, the code's maximum still applies unless the adopted code recognizes the channel.

Cast iron couplings. No-hub cast iron makers and the industry's installation guidance commonly call for a hanger close to each coupling, often within 18 in, and for bracing against sway at changes of direction on larger sizes, because the coupling is a rubber gasket that will let the pipe deflect. Treat that as part of the support layout, not an extra.

Why each material sits where it does

Plastic DWV at 4 ft. PVC and ABS are stiff at room temperature but creep under sustained load, and a drain carries water and solids along its bottom. At 1/4 in per ft, a sag of a fraction of an inch between hangers can flatten or reverse the grade over that span and leave standing water. The spacing protects grade as much as the pipe.

CPVC tighter in small sizes. Small CPVC carrying hot water softens enough to bow between supports. The 3 ft row is that.

PEX at 32 in. Flexible tubing bellies between supports, more so when hot. A belly in a hot line traps air at the crown and sediment at the low point. PEX also expands lengthwise with temperature far more than copper, so supports should hold it without pinching, and a straight hot run needs room to move at its ends or a loop.

Copper wider. Rigid and light; the larger the tube, the stiffer it is, which is why the larger sizes go to 10 ft.

Cast iron at 5 ft, or 10 with 10 ft lengths. Heavy pipe on flexible couplings. The weight of an unsupported coupling is what makes a joint drift and weep.

Hanger material and fit

Galvanic contact. Copper hangs from copper or copper-plated hangers, or from steel hangers with an isolating liner; bare steel in contact with copper in a damp space corrodes. The codes require hangers of a material that will not promote galvanic action (IPC Section 308, in substance).

Plastic and PEX. Use hangers that do not cut or pinch: smooth straps with no sharp edges, plastic clips sized to the tubing, and never a nail-on strap driven tight over PEX. Vertical risers need a support at the base sized for the column, not only the mid-story guide.

Fire and sound separations. Where a support penetrates or attaches at a rated assembly, the firestopping detail governs the attachment; that is a building code question for the assembly, not this table.

What missing support looks like on a service call

Support problems rarely get called in as support problems. They arrive as one of these:

• A drain that holds water. A camera run shows a belly between two joists on a plastic drain, with a waterline that never clears and paper caught at the downstream lip. The fix is a hanger set to grade at the low point, after the line is cleared; re-hanging without clearing it leaves the sludge in place.
• Banging when a valve closes. A copper line that knocks when a washer solenoid or a single-handle faucet shuts is often water hammer, but a line with long unsupported spans moves and strikes framing when it does, turning a small pressure spike into a loud one. Add supports and an arrester where the code or the appliance maker calls for one; supports alone may quiet it.
• Ticking in the walls as hot water runs. PEX or CPVC lengthening as it heats and dragging through tight straps or holes bored too snug. Loosen or replace the straps with clips that let the tubing slide, and give long straight runs room to move.
• A weeping no-hub coupling. The pipe on one side of the coupling has dropped because the nearest hanger is several feet away. Support both sides of the coupling, then retighten the bands to the coupling maker's torque; tightening alone on a sagging joint does not hold.

Worked example: counting hangers in a basement

IPC jurisdiction, 2021 edition as adopted. A basement finish adds four runs along the joists. Each count below takes the run length, divides by the maximum spacing, rounds up to whole spans, and adds one support so both ends of the run are supported.

• 3/4 in type L copper cold main, 34 ft. Spacing 6 ft (1-1/4 in and under row). 34 / 6 = 5.67, rounds up to 6 spans of about 5.7 ft. Supports: 6 + 1 = 7.
• 2 in PVC drain at 1/4 in per ft, 22 ft. Spacing 4 ft. 22 / 4 = 5.5, rounds up to 6 spans of about 3.7 ft. Supports: 6 + 1 = 7.
• 1/2 in PEX hot line, 20 ft. Spacing 32 in. 20 ft is 240 in; 240 / 32 = 7.5, rounds up to 8 spans of 30 in. Supports: 8 + 1 = 9.
• 4 in no-hub cast iron, 30 ft in 10 ft lengths. The footnote allows 10 ft spacing with 10 ft lengths. 30 / 10 = 3 spans. Supports: 3 + 1 = 4, each placed close to a coupling, with the two inner hangers beside the couplings at 10 ft and 20 ft.

Total. 7 + 7 + 9 + 4 = 27 supports, before any extra at changes of direction, branch connections or the stack base. Re-add by run: copper and PVC are 14 together, plus 9 PEX is 23, plus 4 cast iron is 27.

Check the derived spacing against the maximum. Every derived span is at or under its maximum: 5.7 ft under 6 ft, 3.7 ft under 4 ft, 30 in under 32 in, 10 ft at 10 ft. A count that produced a span over the maximum would mean the rounding went the wrong way.

Grade check on the drain. Over the 22 ft PVC run at 1/4 in per ft, the drain falls 22 x 1/4 = 5-1/2 in. Each hanger is set to the string line, not to the joist, so the 5-1/2 in is spread evenly across the 6 spans.

What would change the answer. If the copper main were 1-1/2 in, the IPC row moves to 10 ft: 34 / 10 = 3.4, rounds up to 4 spans, 5 supports. Under the UPC, as read, 1-1/2 in copper stays at 6 ft: 6 spans and 7 supports, two more hangers for the same run. If the PEX maker's instructions for that tubing called for closer spacing on hot lines, the maker's figure replaces 32 in.

How to verify you got this right

• Each run on the rough-in has its material, size, spacing row and support count noted, from the code on the job file and the maker's instructions where closer.
• Copper and CPVC were read on the correct size row, and plastic risers 2 in and under have a mid-story guide.
• Cast iron hangers sit near couplings, and 10 ft spacing is used only with 10 ft lengths.
• Copper is isolated from steel hangers, and PEX straps hold without pinching.
• Every drain hanger is set to the grade line.

References

• IPC 2021 Section 308 and Table 308.5, as adopted by your jurisdiction.
• UPC 2021 Table 313.3, as adopted by your jurisdiction.
• The pipe and fitting maker's installation instructions, which are part of the listing, and the no-hub cast iron industry installation guidance.
• See related: PEX Installation Procedure Reference; How to Hang a Horizontal Drain at Quarter-Inch Fall.
• See related: Drain Pipe Slope + Venting Quick Reference.