How is the value of a claim like this typically calculated?

The most commonly used measure is the actual, documented cost to repair the undisclosed defect, though in some situations damages are instead calculated as the difference between what you actually paid for the property and what it was genuinely worth given the hidden problem that existed at the time of sale. Punitive damages, additional damages intended to punish particularly egregious conduct rather than simply compensate you for your actual loss, do exist as a legal possibility in cases involving genuine, provable fraud, though they're relatively rarely awarded at this claim level in practice.

Building a credible damages claim generally starts with obtaining two independent contractor repair estimates for the defect in question, and where the dollar amount involved is substantial, commissioning a formal property valuation from a qualified appraiser to establish the value gap more precisely and persuasively.