I was under the house yesterday getting ready to reroute some flex duct so my shop door doesn’t swing into it and discovered that all of my under cabinet vents (kitchen and bathrooms) have extreme condensation issues. Each had at least 1sq ft of rotten subfloor and when I demo’d the cabinet floor (laminated MDF) to get to the subfloor I found the whole underside (MDF) was covered in thick white mold.
I immediately took the moldy MDF outside to give it a lethal dose of radiation and got to work on wiping down the subfloor and drying it out with fans and a dehumidifier. I happen to have a moisture meter so I continually checked how well the subfloor was drying out. It went from over 50% in the worst areas to about 16% in a couple hours, but the areas where the subfloor is clearly rotten underneath (not visible from the top) aren’t dropping below that 18-16% moisture range.
I’m reasonably confident that the root cause of the issue is the static air pressure under the cabinets was high enough to force cold air down through the space between the vent and the subfloor. When that cold air met with the super humid hot air in my vented crawlspace it condensed on the subfloor and the insulation held all that moisture against the wood, further compounding the problem.
Looking for feedback on my current plan of action:
- Properly seal the edges of the vents with spray foam/gap filler so air won’t be pushed down into the crawlspace any more.
- Cut out the rotted sections of subfloor and replace them.
- Replace the moldy laminated MDF (possibly replace the whole vanity)
- Increase the size of the vent grill opening so there isn’t as much static pressure building up under the cabinet/vanity.
What do you guys think? Got any experience with this
lurkingdirk
?
P
Picasso3
if you’re still lurking
Initial discovery:
View attachment 173631
Pre-cleanup
View attachment 173632
Post-cleanup and drying (white residue is dried concrobium)
View attachment 173633
