Alexandria's position along the Potomac River keeps relative humidity above 80% through summer, and tidal flooding from hurricanes and nor'easters regularly pushes water into crawlspaces and lower-level units. Old Town's 18th- and 19th-century brick foundations are inherently porous and often lack functional vapor barriers. A single humid summer can turn a small colony into a serious infestation.
Crawlspace mold on floor joists and HVAC ductwork condensation are the most common loss types in Alexandria. Clogged condensate drain lines in attic air handlers are a frequently missed source that can saturate insulation and sheathing over a single cooling season.
Virginia does not license mold remediators separately; require IICRC AMRT certification and a written scope referencing the S520 protocol. Ask for post-remediation air sampling by an independent industrial hygienist — clearance testing is the only way to confirm the work is complete.