What polybutylene is
Polybutylene is gray, blue, or sometimes black flexible plastic plumbing pipe with crimped or barb-style fittings. It was used widely in residential construction from 1978 to 1995 — including in many Plymouth-area homes built in that window.
Why it fails
Chlorine in municipal water gradually degrades the polymer from the inside out. The pipe walls and especially the fitting connections become brittle and crack or leak — often catastrophically and without warning. The Class Action settlement (Cox v. Shell Oil) reimbursed many homeowners but is now expired.
Identification
Look at the pipe coming into the water heater and the main shutoff. Gray plastic = likely polybutylene. Confirm by checking pipe markings ("PB2110" stamping is definitive).
Replacement
Whole-house PB replacement runs $4,000–$15,000+ depending on accessibility, finish disruption, and home size.
Insurance implications
Many Minnesota homeowners insurance carriers now require PB to be replaced or specifically excluded. Confirm with your carrier before closing.