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 to 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 to $6,000+; under-slab $5,000 to $15,000+Address soonPlumbing
The quick answer
Cast-iron drain pipes (standard before ~1975) corrode from the inside out and often fail hidden inside walls or under the basement slab, where repairs get invasive. In a pre-1975 home with original plumbing, budget for it. Spot repairs start around $500; a main stack is $2,000 to $6,000+; under-slab work $5,000 to $15,000+. Have the drains camera-scoped during your conditions, it's cheap for what it reveals.
You are reading the cast-iron drain pipes page. Type the year the house was built and I will tell you what else tends to be true at that age, what it costs, and what to ask. One number, ten seconds.
Free. No account. Educational and impartial, not a home inspection.
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 to $6,000+; and a full under-slab drain replacement can reach $5,000 to $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
Can I get the drains checked before I remove conditions?
Yes, and you should on any pre-1975 home. A plumber's camera scope shows the inside of the stack and the buried line, and it is inexpensive relative to what it can reveal, including the under-slab section nobody can see.
Does a standard home inspection cover the drains?
Not properly. An inspector will run water and note what is visible, but they do not scope the buried line. A camera scope is a separate service you have to ask for.
Is failing cast iron a reason to renegotiate?
It is one of the stronger ones, because the numbers are large and documented. A main stack replacement runs $2,000 to $6,000+ and an under-slab replacement $5,000 to $15,000+, and a scope video is hard for a seller to argue with.
Can I just repair the bad section?
Spot repairs start around $500 and are common, but the rest of the pipe is the same age and corroding at the same rate. A plumber can tell you whether you are buying years or months.
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.