Cost to Replace Cast Iron Drain Pipes in an Old House

Replacing cast iron drain pipe costs $375 to $900 for a short, easily accessed 30-foot run, but climbs to $10,000-$30,000+ when the pipe runs under a slab and needs full excavation and restoration. Homes built before the 1970s commonly still have original cast iron drain lines, which corrode from the inside out and eventually need replacement.

Cost by replacement method

Why cast iron pipes eventually fail

Cast iron corrodes from the inside as decades of wastewater flow through it, gradually narrowing the pipe's interior with rust scale until it either clogs repeatedly or cracks outright. Unlike a single point-of-failure leak, cast iron corrosion is systemic — once one section is failing, the rest of the run is usually not far behind, which is why plumbers typically recommend full-run replacement over patching a single section.

Signs your cast iron drain pipes need attention

• Recurring clogs or slow drains throughout the house, not just one fixture
• Sewage odor from drains, especially after camera inspection shows scale buildup
• Visible rust flaking or a "flaky" texture on any exposed cast iron pipe
• A plumber's camera inspection showing significant interior corrosion or active cracking

Traditional excavation vs. trenchless lining

Traditional excavation costs less per linear foot in materials but adds significant excavation and restoration costs on top — often pushing a whole-house job into the $10,000-$30,000 range once landscaping, driveway, or flooring restoration is included. Trenchless lining costs more per foot but doesn't require digging up the yard or breaking through slab, which is why it's often the lower total-cost option for longer or harder-to-access runs. It won't work, however, if the existing cast iron is too collapsed or misaligned to support a liner — a camera inspection determines this before you get a quote.

If your issue is isolated to the main sewer lateral rather than interior drain lines, see Sewer Line Replacement Cost: Trenchless vs Traditional.

Prices on this page are researched ranges compiled from multiple public contractor-pricing sources, not quotes from us or a guarantee of what you will pay. Actual costs vary by region, material choice, and job complexity — always get itemized quotes from licensed local contractors before committing to a project. See How We Price for our sourcing methodology.

Frequently Asked Questions

How long do cast iron drain pipes typically last?

Cast iron drain pipes generally last 50 to 100 years, but the corrosion process accelerates significantly in the final 10-15 years, which is when most homeowners start experiencing recurring clogs and odors that signal it's time for replacement.

Can cast iron pipes be repaired instead of fully replaced?

A single isolated crack can sometimes be patched, but because cast iron corrodes uniformly along its length, a plumber will usually recommend full-run replacement once meaningful corrosion is found, since nearby sections are typically not far behind in condition.

Is trenchless lining always cheaper than excavation for cast iron?

Not always per linear foot, but it's frequently cheaper in total once you include excavation and restoration costs for traditional replacement. A camera inspection and quotes for both methods are the only way to know which wins for your specific pipe run.

Do I need to replace all my cast iron pipes at once?

Not necessarily — a plumber can prioritize the most corroded sections first. However, since cast iron degrades as a system, many homeowners choose to replace the full run in one project to avoid paying for excavation and restoration multiple times over a few years.