Cast iron was the standard material for drain, waste, and vent (DWV) piping — the pipes that carry water out of a house — in homes built before roughly 1975. It's durable, lasting about 50–75 years, but it corrodes from the inside out: the pipe scales up, thins, and eventually develops pinholes or cracks. The most vulnerable parts are the horizontal runs and the buried section under the basement slab, which you can't see at all.
Spot repairs from ~$500; main stack $2,000–6,000+; under-slab $5,000–15,000+Address soonPlumbing
Why it matters
Unlike a supply-pipe problem, a failing drain often stays hidden until it leaks inside a wall or under the floor — and the repair is invasive, meaning opened walls or jackhammered concrete. In a pre-1975 home with original plumbing, the drains are a real, age-driven cost worth understanding before you remove your conditions, not after the first backup.
How to spot it
Heavy, dark, dull-grey pipe in the basement (it sounds solid when tapped, unlike plastic); rust flaking or staining on the pipe; slow drains throughout the house; recurring sewer smells; and simply a pre-1975 build with no record of a plumbing update. The definitive check is a sewer-camera scope, which shows the inside of the stack and the buried line to the street.
What it costs
Spot repairs start around $500; replacing a main stack runs $2,000–6,000+; and a full under-slab drain replacement can reach $5,000–15,000+ depending on access and how much concrete has to come up. Costs vary widely with the home's layout.
What to do
Address soon. For any older home, have the drains camera-scoped during your conditions — it's inexpensive relative to what it reveals. Budget for replacement timing based on the pipe's age and condition, and use the findings as a negotiation point. A licensed plumber confirms the scope of work.
Education and triage, not a home inspection. Casaroo flags likely cast-iron drains from the home's age and any pipe visible in photos — a plumber's camera scope is what confirms the true condition, including the buried line. We flag; we don't inspect.
Common questions
What is Cast-iron drain pipes?
Cast iron was the standard material for drain, waste, and vent (DWV) piping — the pipes that carry water out of a house — in homes built before roughly 1975. It's durable, lasting about 50–75 years, but it corrodes from the inside out: the pipe scales up, thins, and eventually develops pinholes or cracks. The most vulnerable parts are the horizontal runs and the buried section under the basement slab, which you can't see at all.
Why does it matter for home buyers?
Unlike a supply-pipe problem, a failing drain often stays hidden until it leaks inside a wall or under the floor — and the repair is invasive, meaning opened walls or jackhammered concrete. In a pre-1975 home with original plumbing, the drains are a real, age-driven cost worth understanding before you remove your conditions, not after the first backup.
How can I spot it?
Heavy, dark, dull-grey pipe in the basement (it sounds solid when tapped, unlike plastic); rust flaking or staining on the pipe; slow drains throughout the house; recurring sewer smells; and simply a pre-1975 build with no record of a plumbing update. The definitive check is a sewer-camera scope, which shows the inside of the stack and the buried line to the street.
How much does it cost to fix?
Spot repairs start around $500; replacing a main stack runs $2,000–6,000+; and a full under-slab drain replacement can reach $5,000–15,000+ depending on access and how much concrete has to come up. Costs vary widely with the home's layout.
Lifespan is an estimate that varies with water chemistry and use; a sewer-camera scope is the reliable way to confirm condition — confirm with a licensed plumber. Casaroo flags, it does not inspect.
Last reviewed 2026-06-29.
This guide is general education, not a home inspection and not advice for your specific property — always
consult the appropriate licensed professional, and get a licensed home inspection before you remove conditions
or buy. Cost ranges are 2026 estimates that vary by region, size, and access; confirm specifics with a
qualified professional.