Poor Drainage and Waterproofing
What is that musty smell in the basement? Probably mold. Back in the old days, neither underfloor drainage nor perimeter drainage was provided in a manner equivalent to what is done today. With waterproofing of foundation walls and slab floors, it is the same story.
Issues usually do not materialize in just a few years, but if your home is 50 or more years old, the perimeter and underfloor drainage is likely laughably insufficient by today’s standards, and unless it has been resolved and updated, is very likely to pose a problem at some point — if it hasn’t already. For many older homes, perimeter and underfloor drainage was not provided at all.
You might see signs of mold on the walls of an old home, but more often you will smell the musty gasses released by mold hidden in walls, attics and underfloor framing. Much has been written about the dangers of mold to the health of a structure and, more important, its inhabitants.
If you smell the noxious, gassy byproduct of the mold anywhere, consider a thorough inspection by a professional. This can potentially be a major issue, as the cost to remove mold and properly install new drainage and waterproofing in a very old structure sometimes is not economically feasible.
Photo: Classic Installations, original photo on Houzz