Cast iron versus PVC is a choice about the installed drain system: sound, movement, support, service conditions and the connections that fit. Pipe price alone leaves out much of the job. A material that suits one stack or branch does not automatically suit the next.
This comparison concerns building drain, waste and vent (DWV) pipe, using Charlotte Pipe’s current no-hub cast iron and solid-wall Schedule 40 PVC documents as examples. It does not compare drinking-water pressure pipe, approve a material under your local code or recommend an exact purchase. We reviewed documents, without cutting, installing or sound-testing pipe.
The nominal size is not the outside measurement
Charlotte’s January 2026 cast iron dimensional catalog (charlottepipe.com), page 3, separates barrel diameter J from spigot diameter M. Its April 2026 plastic DWV catalog (charlottepipe.com), page 7, gives average outside diameter for solid-wall PVC. Keep those field names with the numbers.
| Nominal size | No-hub iron barrel J | No-hub iron spigot M | Solid-wall PVC average OD |
|---|---|---|---|
| 3 in. | 3.35 ± 0.09 | 3.41 ± 0.09 | 3.500 |
| 4 in. | 4.38, +0.09 / −0.05 | 4.44 ± 0.09 | 4.500 |
These are different product dimensions, not a guarantee that a coupling will fit your existing pipe. Do not substitute a barrel reading for a spigot reading, or assume an older hub-and-spigot cast iron pipe matches this no-hub table. Measure and identify the actual ends, then match the specified connection.
The plastic catalog separates solid-wall DWV, foam-core DWV, sewer pipe and thin-wall products. Our Schedule 40 versus 80 guide explains why the print line and application matter beyond color or a familiar nominal size.
Ask about the route through the building
For a drain beside a bedroom or living space, include sound control in the comparison. Charlotte’s January 2016 sound-experiment notice (charlottepipe.com) reports that cast iron was the quietest material tested, alongside solid-wall and foam-core PVC with and without insulation. It explicitly calls the test an experiment rather than an endorsement.
That supports discussing cast iron as a sound-control option; it does not predict a decibel level in your room. Pipe routing, the surrounding construction, support and contact with framing belong in the proposed design. Ask what the quote includes for each alternative. This review did not watch the embedded test video or reproduce its experiment.
Different movement needs a system plan
The June 2026 plastics manual (charlottepipe.com), pages 45 and 48–49, ties support and thermal movement to pipe size, temperature, loading and layout. Its worked PVC example gives 1.08 inches of expansion for a 60-foot straight run changing from 70°F to 120°F. That is a calculation example, not a ready-made support or expansion-joint design.
The February 2026 cast iron manual (charlottepipe.com), page 46, publishes a different expansion rate and discusses rigid-pipe burial. A light pipe is not permission to omit supports, and a heavy pipe is not proof that soil or framing can carry the proposed installation. Have the installer identify the applicable support, movement and bedding requirements.
Service conditions matter to durability. The iron manual’s pages 6–7 flag special waste streams and soil-related corrosion considerations. PVC avoids iron rust, but that does not establish chemical compatibility, sound joints or correct installation. No universal 50-, 75- or 100-year life, root-proof claim or remaining-life estimate for an existing pipe follows from this comparison.
Compare the same finished job
For each material option, have the written scope identify:
- The pipe family, sizes, route and condition of the pipe being retained.
- Supports, movement allowance, bedding and any structural work.
- Required fire-rated penetration systems, sound treatment and wall or floor restoration.
- Exact transition fittings, connection instructions, inspection and testing.
Charlotte’s currently linked CPF-9 transition drawing, dated June 2020 (charlottepipe.com), illustrates one specific arrangement: a PVC 119 adapter and a standard CISPI 310 no-hub coupling. Its reference-only notice defers to project instructions and local requirements. It does not approve every rubber coupling or every old cast iron end. Our PVC repair-coupling guide covers the separate repair-part question.
Ask a qualified contractor to assess the existing system before removing a stack or accepting a replacement scope. This page supplies no cutting, temporary support, firestop, solvent-welding or pressure-test procedure.