If your house was built before 1975, the drain pipe inside it is probably cast iron. It was excellent material — durable, quiet, fire-resistant — and it has a service life of roughly 50 to 80 years.
Do the arithmetic on a 1962 house and you arrive at the reason this is one of the most common four- and five-figure surprises in American home ownership.
How cast iron fails
It corrodes from the inside out, and the mechanism is worth understanding because it explains why the outside can look perfect while the pipe is nearly gone.
Wastewater is mildly acidic, and the gases above the flow line — particularly hydrogen sulfide — are considerably more aggressive. Over decades the interior surface builds up tuberculation: rough, scaly corrosion product that narrows the bore and traps solids, which accelerates the process further.
Failure typically shows up in this order:
- Scaling and reduced bore — slow drains, recurring blockages, a rough interior on camera.
- Channeling — the invert (the bottom of the pipe, permanently wet) corrodes fastest and thins first.
- Perforation — a hole in the invert. Water escapes; on an under-slab line it saturates the soil beneath the house.
- Structural loss — the bottom of the pipe is effectively gone, leaving a channel in soil with the pipe crown arching over it.
A camera shows exactly which stage you are at, which is why a scope is worth far more on a cast iron house than on a modern one.
Replacement cost
| Location | Cost per foot | Notes |
|---|---|---|
| Exterior lateral, open trench | $50–$250 | Same as any lateral replacement |
| Accessible basement or crawlspace | $80–$200 | No demolition; the easy case |
| Under a basement slab | $150–$400 | Concrete cutting, spoil removal, reinstatement |
| Under a slab-on-grade with finished floors | $200–$450 | Add flooring loss and containment |
| Vertical stack in a wall | $120–$300 | Add drywall, tile and finishing |
| Whole-house repipe, 1,500–2,000 sq ft | $8,000–$30,000 | Wide range; depends entirely on access |
The distinction that governs the number is accessible versus buried. Cast iron hanging in an open basement is straightforward — cut it out, hang PVC, done. The same pipe under a slab means concrete demolition, excavation inside the house, dust containment, spoil carried out by hand, then concrete, then flooring. The pipe work is a minority of the bill.
How to judge remaining life
Do not replace on age alone. Cast iron ages very unevenly depending on water chemistry, use pattern and how much of the pipe sits permanently wet.
Most professional inspectors grade what they see on camera against the NASSCO PACP (Pipeline Assessment and Certification Program) standard, which rates pipe defects on a 1-to-5 scale from minor to severe — the categories below follow that same logic.
What a camera tells you:
- Light scale, full bore visible — years of life left. Monitor and re-scope in five years.
- Heavy tuberculation, bore noticeably reduced — you are in the management phase. Jetting will help; the underlying loss will not reverse.
- Visible channeling in the invert — the wall is thinning where it matters. Plan and budget.
- Any perforation, or soil visible through the wall — replace. On an under-slab line this is also actively undermining your foundation bedding.
High-pressure jetting on a pipe whose invert has thinned to a few millimeters can perforate it. That converts a slow-drain problem into a leak under your slab. A competent operator identifies the material and the corrosion stage on camera first and drops the pressure. If a company quotes jetting on a pre-1975 house without asking what the pipe is made of, that is a meaningful signal. See hydro jetting cost.
Repair options and what each is worth
Full replacement with PVC or ABS
The definitive answer. Modern plastic drain pipe is immune to the corrosion mechanism and has a 50-to-100-year service life. Where the pipe is accessible, this is usually the right call and not especially expensive.
CIPP lining
A resin liner cured inside the existing pipe. Genuinely useful on cast iron, because it avoids cutting a slab — which is where the money is. $80 to $250 per foot, and it can be installed through existing access points.
The condition: the host pipe must retain enough structural integrity to support the liner during installation. A pipe whose invert is gone cannot be lined, because there is nothing to line against. Ask for the footage that shows the wall is intact.
Sectional or spot repair
Reasonable for one localized failure in otherwise sound pipe. Rarely the right answer on cast iron of a certain age, because the whole run is the same material, laid on the same day, in the same conditions — if one section has perforated, the rest is on the same trajectory. Fixing three feet of an eighty-year-old system is usually a way of paying for the same excavation twice.
Descaling
Mechanical chain-flail descaling removes tuberculation and restores bore. It buys time on a pipe with wall thickness remaining, and it is a legitimate preparatory step before lining. It is not a repair, and on a badly thinned pipe it is a risk.
The under-slab case
This is where cast iron becomes genuinely serious, so it deserves stating plainly.
An under-slab line that has perforated leaks continuously into the soil beneath your house. Depending on soil type, that produces one of two problems: saturated expansive clay that swells and lifts the slab, or fines washed away leaving voids and the slab settling into them. Both show up as foundation symptoms — cracks in drywall, doors that stop closing, uneven floors — long before anyone thinks about a pipe.
If you have a pre-1975 slab-on-grade house with new foundation movement, a sewer camera inspection is worth running before you engage a foundation contractor. The order of operations matters: repairing the slab without fixing the leak means repairing it twice.
I’ve walked into more than one pre-1975 house where the owner had already called a foundation contractor before anyone thought to look at the pipe. A few years back, on a job where the family was watching cracks creep across two rooms and was ready to sign off on foundation piers, we ran a camera through the old cast iron line first and found a perforation quietly saturating the soil under the kitchen. Once that pipe was fixed, the movement stopped — no piers needed. That order of operations is the whole ballgame on these old houses.
Insurance
Corrosion is the textbook definition of gradual deterioration, and standard homeowners policies exclude it. Where a claim sometimes succeeds is on the consequences: sudden water damage to finishes caused by an abrupt failure may be covered even where the pipe itself is not. Many policies also cover “tear-out” — the cost of accessing the pipe through the slab — while excluding the pipe repair.
Read the tear-out provision specifically. On an under-slab job it is frequently the majority of the cost. See who is responsible for sewer line repair.
Frequently asked
How do I know if I have cast iron pipe?
It is dark gray, magnetic, and sounds dull rather than hollow when tapped. In a basement it will be visibly heavy pipe with hubbed joints. A camera identifies it immediately, along with the corrosion stage — which is the part that actually matters.
Should I replace it before it fails?
Only if the camera shows you are close. Age alone is not a reason — plenty of eighty-year-old cast iron is still serving. Scope it, read the invert condition, and decide from that. What is worth doing proactively is replacing accessible sections during any renovation that already has the floor or wall open.
Can cast iron be lined instead of replaced?
Yes, where the wall retains enough integrity to support the liner. This is the single biggest cost saver on under-slab work, because it avoids cutting concrete. It is not viable where the invert has been lost.
Why are my drains slow in a house with cast iron?
Tuberculation. Decades of internal corrosion has narrowed the effective bore and roughened the wall, so solids catch where they would once have passed. Descaling or jetting restores flow temporarily; the wall loss is permanent.
Is cast iron better than PVC?
For noise, yes — noticeably quieter, which is why some builders still specify it for stacks in multi-story construction. For longevity in a drainage application, no. PVC does not corrode, which is the failure mode that ends cast iron.
Pricing surveyed August 2026. See the Methodology and the Disclaimer.
