Chronic high humidity + MVOC smell in wooden multi-story home (Panama, climate zone 1A) — vapor trap + air sealing remediation plan

A homeowner in Panama posted about a moisture problem worth knowing even if you don't live in a hot, humid climate. His wood-framed, multi-story house has run high indoor humidity and a musty "wet hay" smell since it was first built. The likely cause: the wall assembly has foil facing on both sides of the foam board insulation, plus a foil radiant barrier further out. That combination can trap moisture inside the wall cavity, with no way for it to dry outward. The only path left for that damp, smelly air is inward, through gaps around electrical boxes, baseboards, and plumbing lines.

The damage shows up as swollen trim, wet drywall, and mold that tested as a Penicillium-type species in the worst room. Portable dehumidifiers bring humidity down in a room only for it to rebound once shut off, which points to ongoing air leakage rather than a lack of dehumidifying power. Humidity levels also vary sharply room to room, since the five-zone cooling system and staircase layout don't behave uniformly throughout the house.

His plan combines sealing air leaks (outlets, gaps, door weatherstripping), adding bathroom and kitchen exhaust fans, and using a dehumidifier's fresh-air intake to push the house slightly positive so outside air stops sneaking in through cracks. For most homeowners, the lesson is broader: layering multiple vapor-blocking materials on a wall without a way for trapped moisture to escape can cause long-term hidden damage, and persistent musty smells or humidity that won't hold steady are signs worth investigating early.