2026 COST ANSWER
Cast-iron drain replacement can cost hundreds of dollars for a short accessible run, several thousand dollars for a plumbing stack, or $3,000–$20,000 when failed piping sits beneath a slab.
Angi's July 2026 cast-iron replacement guide uses $375–$900 for a 30-foot replacement run with labor, but its own location table moves to $8,000–$10,000 for a basement overhead sewer line and $3,000–$20,000 for under-slab work.
HomeAdvisor's June 2026 plumbing-stack data provides another useful boundary: stack replacement commonly falls around $3,000–$9,000, with an average near $6,500 and a wider published range extending from $1,500 to $15,000.
That spread is not a contradiction. It is evidence that location and access define the project before pipe length does.
FIRST DEFINE WHICH CAST-IRON PIPE YOU ARE PRICING
“Cast iron pipe” can describe several parts of a drainage system, and they should not be priced as one generic repipe
The Cast Iron Soil Pipe Institute describes cast-iron soil pipe and fittings as products used for sanitary and storm drain, waste and vent systems. That distinction matters because homeowners often use “repipe” to describe both water-supply piping and waste piping even though the systems have different functions, access requirements and failure modes.
Horizontal or sloped piping carrying wastewater from kitchens, bathrooms and other fixtures toward a larger drain.
A major vertical drain can cross several floors, walls and ceilings before reaching the building drain.
Larger drain piping inside the building may run through a basement, crawl space or beneath a slab.
Once the scope moves outside toward the public sewer or septic connection, excavation and trenchless economics become a different cost file.
For the exterior buried lateral, use Sewer Line Replacement Cost. For pressurized water-supply piping inside the home, use Whole-House Repipe Cost.
LOCATION IS THE PRIMARY COST MAP
The same length of pipe can move through four completely different labor environments
The plumber can see the pipe, support it, cut it and install replacement sections without opening finished walls or concrete.
Plumbing labor is joined by demolition, dust containment, drywall or plaster restoration and finish work.
Multiple openings, heavy pipe sections, fixture connections and floor-to-floor sequencing can make one vertical run a major interior project.
Locating the failed run, cutting concrete, excavation, replacement, testing and slab restoration can dominate the price before finish flooring is considered.
Measure pipe length only after identifying what has to be removed to reach that pipe.
VERTICAL STACK REPLACEMENT IS A FLOOR-BY-FLOOR PROJECT
A plumbing stack can be only a few dozen feet long and still cost thousands because every floor adds interfaces
HomeAdvisor's current stack-replacement data centers around $3,000–$9,000, averaging approximately $6,500. Its broader published range reaches $1,500–$15,000 depending on material, length and labor.
The useful comparison is not simply feet of pipe. A vertical stack may connect bathrooms, vent piping and horizontal branch drains while passing through walls, floors and fire-resistance assemblies. Each connection and opening has its own labor and restoration consequence.
Disconnect, support and reconnect branch piping.
Create enough working room for removal and new joints.
Coordinate additional bathrooms, kitchens or vents.
Define where the new stack stops and existing piping remains.
UNDER-SLAB CAST IRON IS A CONCRETE-ACCESS PROBLEM
Angi's $3,000–$20,000 under-slab range shows why a material price per foot is almost meaningless in this location
The replacement pipe may account for only a small share of an under-slab project's total cost. The larger sequence can include camera inspection or other diagnostics, layout, concrete cutting, excavation, pipe removal, bedding, new drainage piping, testing, backfill and concrete restoration.
Define the failed run before cutting the slab.
Cut concrete and create a safe excavation path.
Remove failed sections and install the designed drainage run.
Verify the system before burying the repair.
Backfill and close concrete before finish flooring work.
Do not confuse this with a Slab Leak Repair Cost. “Slab leak” commonly refers to a leak in pressurized water piping. A failed cast-iron building drain beneath the same slab is a gravity-DWV problem with a different diagnosis and replacement sequence.
REPLACEMENT DOES NOT AUTOMATICALLY MEAN REINSTALLING THE SAME MATERIAL
Separate the failed cast-iron system from the material specified for the new work
Current consumer cost data generally prices cast iron above PVC on a material basis. HomeAdvisor currently lists cast iron around $10–$20 per foot before typical contractor markup, with approximately $12.50–$30 per foot after the markup model used in its guide.
Those material figures should not be mistaken for installed replacement costs. Angi's 2026 drain-pipe data likewise shows cast iron among the higher-cost pipe materials but states that location and accessibility materially change the final job.
Often considered in residential replacement scopes where locally permitted and appropriate to the design.
CISPI publishes standards covering hubless and hub-and-spigot cast-iron soil pipe, fittings, gaskets and couplings for DWV applications.
Material selection is a project-design and code question, not simply a cheapest-per-foot decision. The proposal should state exactly which material, fittings and transition method are being installed.
ONE FAILED SECTION DOES NOT PROVE THE WHOLE SYSTEM HAS FAILED
Replacement scope should follow inspection evidence, not the age of the house alone
A localized replacement may be defensible when surrounding pipe condition is acceptable and the failure boundary is clear.
Repeated failures can change the economics from isolated repairs toward sectional or system replacement.
Camera inspection and professional assessment can help define whether deterioration extends beyond one accessible opening.
The repair may need to correct support and alignment rather than simply exchange one pipe material for another.
If the question is whether an exterior sewer line can be repaired rather than excavated, compare Sewer Line Repair Cost and Sewer Pipe Lining Cost. Those are different decisions from replacing interior cast-iron DWV.
PLUMBING AND RESTORATION NEED SEPARATE CONTRACT BOUNDARIES
A drain can be operational while the room around it is still a construction site
WALLS Drywall or plaster openings Is patching included, or does the plumber leave access openings for another contractor?
FLOORS Tile, wood or other finished flooring Under-slab work can require a second restoration budget above the concrete repair.
CABINETRY Kitchen and bathroom built-ins Determine whether fixtures or cabinets obstruct the pipe route.
CONCRETE Cutting and patching The bid should state who owns demolition, excavation, backfill and slab restoration.
FIXTURES Disconnect and reconnect Toilets, sinks and other connected fixtures may require separate handling.
DEBRIS Heavy cast-iron removal Define whether demolition and disposal are inside the plumbing contract.
FOUR DRAINAGE COST FILES
These published examples show why “cost per foot” cannot describe the project without a location
Angi currently uses approximately $375–$900 for a 30-foot replacement run with labor. Treat this as the accessible end of the scope spectrum, not a whole-house benchmark.
HomeAdvisor currently publishes a typical $3,000–$9,000 range, averaging roughly $6,500, because one vertical pipe can require work across several floors.
Angi's cast-iron location table gives approximately $8,000–$10,000 for this scope, illustrating that visible pipe is not automatically a small replacement project.
Angi publishes a broad $3,000–$20,000 range. Concrete access, excavation and restoration explain why this cannot be compared with an exposed branch run on linear footage alone.
NORMALIZE THE DRAINAGE SCOPE BEFORE COMPARING BIDS
Ten lines should match before one cast-iron replacement proposal is actually cheaper than another
PIPE FUNCTION Branch, stack, building drain or exterior sewer? Do not compare different parts of the drainage system.
START / STOP POINTS Exactly where does replacement begin and end? Identify every transition to existing piping.
LENGTH / DIAMETER How much pipe and what sizes? A stack and a sink branch are not equivalent footage.
ACCESS Exposed, concealed or under slab? Access is often more important than material cost.
NEW MATERIAL PVC, cast iron or another approved system? The proposal should identify the replacement specification.
TRANSITIONS How does new pipe connect to retained piping? Couplings and transition points belong in the defined scope.
FIXTURES / BRANCHES Which connections are disconnected and rebuilt? Especially important for stack replacement.
DEMOLITION Who opens walls, ceilings or concrete? Do not hide construction access inside a vague plumbing allowance.
RESTORATION Who closes the building afterward? Concrete, drywall, plaster, tile and paint should have clear owners.
PERMITS / TESTING What inspection and closeout work is included? Requirements depend on the jurisdiction and actual scope.
WHY THIS GUIDE DOES NOT USE ONE CAST-IRON $/FOOT CALCULATOR
A universal multiplier would make the easiest job and the hardest job look falsely comparable
Current published data already demonstrates the problem. A short accessible replacement can remain below $1,000 while an under-slab scope can reach five figures. Multiplying every project by one national installed cost per foot would erase the variable that matters most: access.
A useful estimate therefore starts with pipe function → location → access → repair boundary → new material → restoration, and only then uses footage as a quantity.
HIGH-INTENT PRICE ANSWERS
Cast-iron drain replacement cost in plain terms
How much does it cost to replace cast-iron drain pipe? Published 2026 figures range from hundreds of dollars for a short accessible run to many thousands for stacks or under-slab drains. Location must be defined before the number is useful.
How much does a 30-foot cast-iron replacement cost? Angi currently publishes approximately $375–$900 for a 30-foot run with labor, depending on access.
How much does replacing a plumbing stack cost? HomeAdvisor currently places typical stack replacement around $3,000–$9,000, averaging approximately $6,500.
How much does cast-iron pipe replacement under a slab cost? Angi's current location table uses approximately $3,000–$20,000 because concrete access, excavation and restoration can dominate.
Can cast iron be replaced with PVC? PVC is commonly considered in residential DWV replacement, but the allowed material, transitions and installation requirements depend on the project's design and locally adopted plumbing code.
Is cast-iron drain pipe the same as a whole-house repipe? No. Cast-iron soil pipe is generally part of drain, waste and vent plumbing. Whole-house repiping commonly refers to pressurized water-supply piping.
Does all old cast iron need to be replaced at once? Not automatically. The repair boundary should follow actual condition, inspection findings, access and the economics of repeated failures.
What is usually the biggest cost driver? Access. A visible basement run, a concealed multi-story stack and a drain beneath concrete require very different labor and restoration scopes.
METHODOLOGY & SOURCES
Pricing benchmarks are separated from DWV material and specification guidance
Cost data was reviewed September 6, 2026. Angi supplies current cast-iron replacement and drain-pipe location data. HomeAdvisor provides an independent drain-replacement dataset and current plumbing-stack pricing. CISPI is used only for technical context about cast-iron soil pipe, DWV applications and applicable product standards.
Current accessible-run data plus published location ranges for basement overhead and under-slab replacement.
02 · HOMEADVISOR · JUN. 19 2026 Plumbing Stack Replacement CostCurrent $3,000–$9,000 typical stack range, average cost and wider scope boundaries.
03 · HOMEADVISOR · JUN. 17 2026 Drain Pipe Replacement CostMaterial pricing, accessibility, whole-house drain context and restoration cost factors.
04 · ANGI · JUL. 9 2026 Drain Pipe Replacement CostIndependent 2026 context for pipe material, length, access, permits and post-construction restoration.
05 · CISPI · PRODUCT SPECIFICATIONS Cast Iron Soil Pipe StandardsTechnical context for hubless and hub-and-spigot pipe, fittings, couplings and above- / below-grade DWV use.
06 · CISPI · TECHNICAL HANDBOOK Cast Iron Soil Pipe & Fittings HandbookInstallation, system-design and material context for cast-iron soil pipe and fittings.
This report provides U.S. property cost-planning information, not plumbing design or code advice. Drainage layout, pipe condition, sizing, slope, venting, transitions, fire-resistance assemblies, permits, testing and approved replacement materials must be established for the actual property by appropriately qualified professionals and the authority having jurisdiction.