In this case it was Article I, Section 9 which provides:
Every person is entitled to a certain remedy in the laws for all injuries, or wrongs which he may receive in his person, property, or character; he ought to obtain justice freely, and without being obligated to purchase it, completely and without denial, promptly and without delay, conformably to the laws.
[While the court did not say so, I understand this provision is derived from the fortieth provision of Magna Carta (1215)]
In this new decision, the court extended risk-contribution as a basis for liablility. In granting summary judgment to the defendants, the Circuit Court distinguished the earlier Supreme Court case of Collins v. Eli Lilly which had imposed risk-contribution liability on makers of diethylstilbestrol [DES], opinion para 18. The Court of Appeals affirmed, agreeing that, under Collins, risk-contribution liability was imposed only because the plaintiff there had no other remedy. In the present case, the plaintiff had already settled with the landlords where the lead exposure occurred. In reversing, the Supreme Court said this prior holding did not preclude Article I, Section 9 as a basis for further relief, even though the plaintiff already had a remedy against another party, para. 118 et seq..
The court declined to rule on federal constitutional issues which the defendants asserted would arise if it here permitted plaintiff proceeding against them on a risk-contribution liability theory, para. 165 et seq..
Justice Wilcox dissented. On the state constitutional issue, he noted,
The defendants in this case, contrary to the majority's characterization, do not argue that Article I, Section 9 absolves them from liability. Rather, they argue "[t]he 'Right to Remedy' Clause of the Wisconsin Constitution Does Not Require Extension of Collins."
That is, since the plaintiff is not without a remedy, having already recovered from the landlords, the existing requirements for establishing the other defendants' liablilty should apply. Justice Wilcox went on to say that by extending Collins to this case anyway, the majority's holding went beyond the "conformably to the laws" limitation of the constitutional provision, para. 207
Justice Prosser dissented, and said the majority's holding denies the defendants due process law the the equal protection of the laws under the U.S. Constitution, para. 282 et seq..
Update 2: Summary in the Wisconsin Law Journal