Iowa Code § 614.12: Counterclaim.

A counterclaim may be pleaded as a defense to any cause of action, notwithstanding it is barred by the provisions of this chapter, if it was the property of the party pleading it at the time it became barred, and was not barred at the time the claim sued on originated; but no judgment thereon, except for costs, can be rendered in favor of the party so pleading it.