Hello. I have a small house (10×20) on a trailer that I inherited unfinished and I’m concerned about moisture buildup in the floor, walls and ceiling given the construction techniques. I am located in the pacific northwest. 

First, looking up from underneath the trailer, we see a black poly vapor barrier stapled to the underside of the 2×4 floor joists, which are insulated with 2″ of rigid foam in between the joists. 

The walls, from the outside, are corrugated metal against tar paper, which is stapled upon OSB plywood, which is fastened to 2×3’s, which are insulated in between with 2″ of rigid foam, and then drywall for the interior finish. Part of the room has T&G wood instead of drywall. 

The ceiling, looking up, a combination of drywall and T&G wood, 2″ rigid foam, OSB, tar paper and then metal roofing. 

Given the lack of insulation, the metal siding, etc. I’m concerned that moisture will build up on the underside of the OSB plywood given that it will be quite cold in the winter, especially due to the thermal bridging. 

I’m continuously running a dehumidifier which is keeping the room at 55% humidity, and I am using a heater to keep the space above 62 degrees F. Will this be effective to protect the building from condensation and potential mold problems over time? 

In terms of future renovations, I am considering pulling off the poly vapor barrier underneath and fastening rigid foam insulation instead, being careful to tape and seal seams. I would also consider removing the corrugated siding and roofing and applying rigid foam before putting the siding and roofing back on. Are these sound ideas? 

Thank you!!
Jeff