Short definition
A cast-iron repair flange is a replacement closet flange designed to fit into a cast-iron drain riser whose original flange has corroded or broken. Most use a rubber compression seal expanded inside the iron pipe by tightening bolts. It’s the standard repair for the “broken cast-iron flange” call that’s common in pre-1970 WA homes.
What it is
Two main configurations:
- Inside-fit. A PVC sleeve drops into the existing cast-iron pipe with a rubber compression seal expanded by tightening bolts. The flange ring sits at floor level, ready for closet bolts. Easier install.
- Outside-fit / clamp-on. Clamps over the cast-iron riser with a metal band and a rubber-and-PVC inner sleeve. Useful when the iron lip is damaged but the pipe wall is solid.
Choice depends on remaining iron condition. If the iron riser is solid, inside-fit is straightforward. If the iron is corroded too badly to compress against, full pipe replacement is the only durable answer.
Standard 4-by-3 combo (4-inch outer flange, 3-inch pipe sleeve) covers most residential. Brands shipping current 2026 product: Oatey, Sioux Chief, Fernco — verified at major retailers 2026-04-30.
Why it matters to a homeowner
In a pre-1970 WA home — Capitol Hill bungalow, Tacoma craftsman, Spokane-area mid-century, Anacortes farmhouse — a wobbly toilet on inspection often turns out to be a broken cast-iron closet flange. The original flange ears have corroded through; closet bolts have nothing to grip. The wax ring may also have failed, producing sewer-gas smell and water at the base.
A cast-iron repair flange is the right fix for this scenario. Part is $20 to $50, pro install $200 to $500 depending on access. If the iron pipe itself is corroded too far, the alternative is a much more expensive cast-iron riser replacement ($1,000 to $3,000) or a transition to PVC.
This is technically DIY-capable for someone comfortable lifting a toilet, but the right tools — multi-tool for any cutting, alignment care, and patience — make a real difference. A misaligned repair flange that compresses unevenly is a slow leak waiting to happen.
Common failure modes
- Iron pipe too corroded to compress against. Repair flange leaks; pipe replacement needed.
- Floor cut too small around the pipe. Flange screws can’t reach subfloor; widen the cut and add backer.
- Wrong product on PVC riser. Cast-iron repair flange is for cast iron only; use a standard PVC closet flange on PVC.
Common variants
- Cast-iron repair flange (this entry) vs. standard PVC closet flange.
- Inside-fit vs. outside-fit clamp-on.
- Crescent flange repair strap. A metal strap that captures broken closet bolts on a damaged cast-iron flange ring without replacing the flange — a different (and lighter-touch) fix.
Washington note
The pre-1970 WA housing stock is full of cast-iron drainage stacks and closet flanges. Iron flanges in those homes are reaching end-of-life — corroded ears that snap on the next over-tight closet bolt, or pinhole-leaking flange rims. The cast-iron repair flange is so routinely needed in WA that it’s stocked by every major hardware store in the region. WAC 51-56 doesn’t explicitly call out repair flange products by name; Oatey, Sioux Chief, and Fernco repair flanges all comply with UPC 408 closet-flange requirements and pass WA jurisdiction inspections in standard installations.