If you are walking through a seemingly perfect home built in the 1980s or early 90s, do yourself a favor: Look under the kitchen sink.

If you see a flexible plastic pipe that is Gray, Blue, or Black, you might be looking at Polybutylene (PB).

For decades, this material has been the bane of homeowners, insurance agents, and plumbers alike. It is the single most common reason for plumbing-related walk-aways in real estate transactions. Here is why this "miracle pipe" turned into a disaster—and what it costs to fix in 2026.

What is Polybutylene?

Used heavily from 1978 to 1995, Polybutylene was a cheap, easy-to-install alternative to copper. It was installed in over 10 million homes across the U.S., particularly in the "Sun Belt" and Pacific Northwest.

How to Identify It:

Color: Usually gray (most common), but can be blue or black.
Markings: Look for the code PB2110 stamped on the side.
Location: Check near the water heater, under sinks, or at the main water shut-off valve.

Why Does It Fail?

PB pipe isn't necessarily weak on its own. The problem is chemistry. Polybutylene reacts poorly to the chlorine and chloramine found in municipal water supplies. Over years, the water effectively "rots" the pipe from the inside out, causing the plastic to become brittle and flake away.

The "Silent" Killer: Unlike copper, which usually develops a small "pinhole" leak that gives you a warning, PB pipes often burst completely. They tend to fail at the fittings (the metal or plastic crimp rings), causing a sudden, catastrophic flood that can cause tens of thousands of dollars in damage in minutes.

The Insurance Problem

This is the biggest headache for new buyers. Many major home insurance carriers will not write a new policy for a home with known Polybutylene plumbing. Others will insure the home but specifically exclude water damage caused by PB pipe failure.

If you are buying a home with PB pipes, your mortgage lender may require you to replace them before closing, or you may be forced to pay a significantly higher insurance premium.

The Solution: Whole-Home Repipe

Unfortunately, there is no "repair" for Polybutylene. You cannot patch it, and you cannot join it to modern PEX pipe reliably. It is a ticking time bomb that must be removed.

2026 Replacement Costs: Repiping a standard 2-bathroom home usually takes 3–5 days.

Average Cost: $4,000 – $10,000 (depending on home size and drywall access).
The Process: Plumbers will cut small access holes in your drywall, remove (or abandon) the old PB lines, and run new, flexible PEX (Cross-linked Polyethylene) or Copper piping.
The ROI: While expensive, replacing PB pipe immediately increases your home's resale value and makes it insurable.

Conclusion

Polybutylene is part of the "Dangerous Pipes" club, right alongside Lead and Orangeburg. If you have it, don't panic—but do plan. It is not a matter of if it will leak, but when.

Buying a home with suspicious gray pipes? Book a Pre-Purchase Plumbing Inspection to know the true cost before you buy.

Sources & Further Reading

InternACHI: Polybutylene for Inspectors
Square One Insurance: Polybutylene Piping: Why it’s a problem