## Facts

- Homeowners alleged that a home plumbing system using cross-linked polyethylene (PEX) tubing and brass crimp fittings was defectively designed and likely to fail prematurely.
- The claimed defect focused on brass fittings with relatively high zinc content that allegedly corroded and cracked (including stress corrosion cracking), causing leaks and property damage.
- The products were marketed as easier to install, cheaper, and longer lasting than copper plumbing systems, and were sold with a 25-year limited warranty.
- Multiple suits were centralized in a multidistrict litigation in the District of Minnesota.
- Plaintiffs asserted claims including negligence, breach of implied warranty of merchantability, breach of express warranty, and claims under Minnesota consumer-protection statutes.
- At class certification, plaintiffs relied on expert testimony from a statistician analyzing warranty-claims data and a corrosion engineer addressing failure mechanisms.
- The district court denied the defendants’ Daubert motions, certified classes for warranty and negligence claims, and denied certification for consumer-protection claims due to individualized reliance and causation issues.

## Issues

1. Whether the district court abused its discretion in considering and crediting plaintiffs’ expert testimony at the class-certification stage under Daubert.
2. Whether the district court abused its discretion in certifying Rule 23(b)(3) classes for warranty and negligence claims, including whether common issues predominated over individual issues.

## Decision

- The court of appeals affirmed the class-certification order.
- The court held the district court did not abuse its discretion in denying the Daubert challenges and considering the experts’ opinions for the limited purpose of class certification.
- The court held Rule 23(b)(3) predominance was satisfied because common questions about an alleged uniform defect and uniform warranty obligations could be proved with common evidence.
- The court left undisturbed the denial of certification for consumer-protection claims, which no party appealed.

## Legal Principles

- A district court must conduct a rigorous Rule 23 analysis, and Daubert reliability principles apply to expert testimony used at class certification.
- The Daubert inquiry at class certification may be tailored to the purpose of the evidence at that stage; the court has discretion in determining how to assess reliability so long as the analysis is sufficiently searching.
- Predominance under Rule 23(b)(3) can be met in product-defect and warranty litigation when liability turns on common proof of an alleged uniform design defect and standardized warranty terms, even if individualized issues remain for causation-in-fact in particular homes or for damages.
- Individual variations (e.g., installation conditions, water chemistry, and property-specific damages) do not necessarily defeat certification where classwide resolution of defect and breach questions materially advances the litigation.
- Superiority may be satisfied where many similar claims would be impractical to litigate individually and class treatment reduces duplicative proceedings and inconsistent rulings.

## Conclusion

The Eighth Circuit upheld certification of negligence and warranty classes challenging an allegedly defective plumbing system, approving the district court’s context-sensitive Daubert review at class certification and concluding that common defect and warranty questions predominated despite individualized issues concerning causation details and damages.


In re Zurn Pex Plumbing Prods. Liab. Litig., 644 F.3d 604 (8th Cir. 2011)