Description:

Multi-story wood-framed home in Panama, Central America (ASHRAE climate zone 1A — hot-humid, near-equatorial, minimal diurnal swing, high year-round outdoor absolute humidity). Looking for feedback on a diagnosis and remediation plan for chronic elevated indoor RH and a persistent “wet hay” MVOC smell that’s been present since the house was first occupied.

Envelope: Wood-framed wall assembly, outer to inner: Dutchlap wood siding → 1″ air gap → perforated R-foil radiant barrier → 3/4″ double-sided foil-faced polyiso board → 2.5″ mineral wool cavity insulation → 5/8″ drywall interior. The polyiso’s foil facing on both sides acts as a vapor barrier on each face, and combined with the perforated foil layer outboard of it, appears to sandwich the cavity — blocking outward diffusion. That leaves interior air leakage paths (electrical boxes, baseboard gaps, plumbing penetrations) as the dominant route for humid/MVOC-laden cavity air to reach living spaces.

Roof/attic assembly, outer to inner: corrugated metal roof → 4″ gap → perforated R-foil radiant barrier stapled to rafter undersides → attic cavity (crawl-height) → 6″ R-11 fiberglass batt directly over 5/8″ drywall ceiling. Attic is naturally vented at the ridge cap and laterally  though a gable vent).

I want to ask the group here: does the wall assembly constitute a moisture trap as I’ve described it, or am I missing something in the vapor drive/permeability picture?

HVAC: Five-zone VRF — Zone 1 ground floor, Zones 2–3 den/master bedroom (1st floor), Zones 4–5 two bedrooms (2nd floor). VRF setpoints are kept low overnight (cool rooms are a priority for restorative sleep), which raises the bar for the dehumidification system to manage RH/condensation risk at that setpoint rather than relying on a warmer setpoint to reduce latent load. Adding dedicated dehumidification: AlorAir WHD 120 (ground floor/garage), AlorAir HDi 90 in the attic; second HDi 90 planned for first floor. Units are currently just temporarily staged in the hallways — they’ll pull local RH down to ~60% but it rebounds to the mid-70s within a short time of shutting off, which points to an ongoing infiltration load rather than a capacity problem.

Diagnosis/Symptoms: Peeling back swollen bathroom trim exposed wet drywall matching the house’s ambient odor. The same smell shows up when cutting circular saw access holes to chase wires in interior partition wall cavities, suggesting the elevated RH/MVOC condition isn’t confined to exterior walls but has spread into interior partitions as well. While moving the HDi 90 between rooms for testing, I’ve also noticed sharp room-to-room variation — one room can be down to 60% RH while the room immediately adjacent sits in the mid-70s. With five independent VRF zones and an offset staircase layout (so stack effect doesn’t behave uniformly floor to floor), the house seems to have developed distinct humidity microclimates/pockets rather than one uniform condition, possibly with some thermocline-like stratification between rooms as well.

Remediation underway: Air-sealing electrical boxes and penetrations (caulk, foam gaskets, duct seal putty), prioritizing exterior walls. Improving door gaskets/weatherstripping (windows are already fairly tight, so doors are the bigger leak point). Panasonic WhisperGreen fans installed in en-suite bathrooms and laundry, running 30 CFM continuous baseline with a mix of humidity-sensor and occupancy-boost control (boost setting is 130 CFM); the humidistat mode sometimes runs for extended periods. Installing a 4-speed, 1200 CFM range hood vent in kitchen, curremtly there is no range hood vent. Using the WHD 120’s fresh air port to introduce conditioned makeup air and push the house toward slight positive pressure to stop infiltration at the source. Planning attic bypass sealing , plus permanent ducting of the dehumidifiers once sizing/placement is finalized.

Closing questions / DIY testing:

Does this sequencing (air seal → positive pressurize → dehumidify) make sense for a 1A climate with a pre-existing vapor trap, or is there a failure mode I’m missing?

One thing I’m not fully clear on: does it make sense to be injecting outside air via the WHD 120’s fresh air port while the bathroom exhaust fans are simultaneously pulling conditioned indoor air back out? Trying to understand if these should be balanced against each other (total exhaust CFM vs. fresh-air CFM) to actually net out to positive pressure, or if I’m overthinking the interaction.

No blower-door contractors available in my area, so looking for DIY alternatives or other low-cost/hand-tool methods to confirm where infiltration is actually happening before I keep chasing it room by room.

Closing note: I’m doing all of this myself — no local contractors familiar with wood-frame construction or proper HVAC/moisture practice that I’ve been able to find. Working with basic hand tools, hygrometers, and a pin-type moisture meter. Took one petri dish swab in the worst-affected room (master bedroom) and got growth that looks like Penicillium-type mold. That room has been running 70%+ RH for a while now, and it’s starting to feel like it’s taking a toll on our health — motivated to get this right, but appreciate any outside eyes on the plan.

Cheers, 

Tito