You can sue the seller of the house for fraud.  Fraud is the intentional misrepresentation of a material fact made with knowledge of its falsity and with the intent to induce your reliance upon which you justifiably relied to your detriment.  In other words, by concealing the cat urine problem, the seller induced your reliance on their misrepresentations of the condition of the basement and you justifiably relied on their misrepresentations to your detriment by purchasing the house.  You would not have purchased the house had you known about the actual condition of the house damaged by the cat urine.Your damages (the amount of compensation you are seeking in your lawsuit for fraud) would be either the benefit of the bargain or your out of pocket loss.Benefit of the bargain means that a defrauded purchaser may recover the difference between the real and represented value of the property purchased regardless of the fact that your actual loss might have been less.Out of pocket loss for fraudulent misrepresentation permits recovery of the difference between the price paid and the actual value of the property acquired.