231 Pa. Code § 1030 : RULES OF CIVIL PROCEDURE — GENERAL — ACTIONS — CIVIL ACTION —PLEADINGS — New Matter

(a) Except as provided by subdivision (b), all affirmative defenses including but not limited to the defenses of accord and satisfaction, arbitration and award, consent, discharge in bankruptcy, duress, estoppel, failure of consideration, fair comment, fraud, illegality, immunity from suit, impossibility of performance, justification, laches, license, payment, privilege, release, res judicata, statute of frauds, statute of limitations, truth and waiver shall be pleaded in a responsive pleading under the heading "New Matter." A party may set forth as new matter any other material facts which are not merely denials of the averments of the preceding pleading.
(b) The affirmative defenses of assumption of the risk, comparative negligence and contributory negligence need not be pleaded.

231 Pa. Code § 1030