Can you identify this white material and why it is a cause for concern? I see this fairly frequently, especially in crawl spaces and attics. You might think it is white mold (testing it would give a definitive answer) but it is most likely wood-destroying fungus. As the name suggests, this fungus actually breaks down and digests the wood. Over time, it can cause significant wood rot and damage and make the structure – in this case the support beams holding up the house(!) – less stable, compromising the entire structure. In some cases, the rot is so bad I can insert a screwdriver into the entire beam. This kind of damage can often be mitigated by adding (or “sistering”) another beam next to the damaged beam, giving your floor structure the support it needs. Discovering these kinds of concerns is so important, whether you are buying the home or you’ve lived in it for some time. Home inspections are a very good way to identify these issues before they become very serious (and expensive) problems.