If floor beams appear to be rotting, could the urethane foam they’ve been sprayed with have sealed in moisture?
An existing moisture problem is most likely the cause of rotting joists and beams in this case. But covering moist wood with insulation could have trapped the moisture and caused even further decay. These wood members should need to be allowed to breathe.
The major causes of rot in floors and beams are high relative humidity in the basement or crawl space, and moisture from plumbing leaks or a failure at the building envelope. Repairing a large area of damage could potentially be a huge job, but if only a small section of your crawl space or basement is affected, simply address the root cause of the problem and replace the rotten joists and beams. Replacing the beams is key; if you install new beams beside the rotten ones the rot could spread.