Short definition
A closet flange (or toilet flange) is the slotted ring at floor level into which closet bolts slide and a toilet bowl bolts down. The flange itself is glued, screwed, or compressed onto the top of the soil pipe. The wax ring seals between the bowl horn and the flange. When a toilet rocks, leaks at the base, or smells of sewer gas, the flange is usually the suspect.
What it is
In modern construction, the flange is PVC — solvent-welded to the PVC drain stub and screwed to the subfloor. In older WA homes (pre-1970), the flange is cast iron — poured or leaded into a cast-iron drain. Both have a horizontal ring at floor level with two slots opposite each other for closet bolts.
The flange should sit about 1/4 inch above the finished floor. That’s so the bowl horn projects down into the flange opening and the wax ring has a continuous compressible seal between bowl and pipe. If the flange ends up below the finished floor — common when tile is added to an old bathroom — the wax ring can’t seal reliably, and the fix is either a wax ring with a deeper horn, stacked wax rings, or a flange extender ring.
UPC 408 (and most adoptions) requires the flange anchored to the floor and the joint between bowl, flange, and wax sealed against vermin.
Why it matters to a homeowner
The closet flange is the single highest-impact piece of toilet hardware homeowners never see. Three failure modes account for nearly every “toilet leaks at the base” or “toilet rocks” call:
- Broken flange ears. Closet bolts have nothing to grip. Toilet rocks. Use a half-moon repair strap (crescent strap) or replace the flange.
- Cast-iron flange corroded through. Common in pre-1970 WA homes. Cure: cast-iron repair flange — a rubber compression seal with a PVC sleeve that snaps into the damaged riser. (See repair-flange-cast-iron.)
- Flange below finished floor. Tile-added bathrooms. Use a flange extender ring or a thicker wax ring with horn.
Pro flange replacement runs $200 to $500 depending on access and pipe material. PVC flanges cost $5 to $15; cast-iron repair flanges $15 to $40; offset flanges $15 to $30.
Common failure modes
- Broken ears. Repair strap or replacement.
- Corroded cast iron. Repair flange replacement.
- Below-floor mounting. Extender ring or thicker wax ring.
- Not anchored to subfloor. Re-screw to subfloor.
Common variants
- PVC closet flange (modern) vs. cast-iron (legacy WA) vs. ABS (West-Coast residential).
- Standard flange (drain centered on flange) vs. offset flange (drain shifted 1 to 2 inches laterally — weaker, only when redoing the drain isn’t feasible).
- Inside-fit (slips inside cast iron) vs. outside-fit (over PVC).