Me wrote:
....
I have a storage room that runs the length of the front of the house
under the porch. It's around 36' x 3' and has block walls.
....
Well... I went ahead and insulated that metal - coated it with the
greatstuff spray foam and set rigid foamboard insulation sheets under the
coating. Seems to have worked pretty well since I no longer have any
visible condensation - at times it was dripping in there like a
rainforest before I coated the ceiling.

While I was at it, I also thorosealed the walls - both the three under
grade and the one that borders the basement. The dashes in the wall
above represent an insulated steel door going from the storage area to
the basement.

Anyway, it's all done now, but the results weren't what I expected... I
put a humidity guage in there and while I don't see any visible water or
condensation, it's pretty much stuck around 90% humidity. In the
basement area it stays at around 50%-60%, but that goes up if I leave the
door to the storage area open.

Any idea what could be causing this? I need to get that number down so
that I can actually use that storage area for storage!

Yeah, you have a closed area underground in an area that outside
obviously is saturated or may even have underground water flow. You've
slowed down the moisture infiltration, but not completely stopped the
vapor flow.

Only way you can do that is to start on the outside and figure out what
the source of the water is and either divert it away from the basement
walls before it approaches them and then add additional waterproofing
outside as well.

Almost surely you would still need a dehumidifier in the storage area to
keep the humidity down. You could try the expedient of a dehumidifier
now, but it's likely not going to be sufficient by itself, but it just
might if enough capacity and you once get it dried out some...but given
the symptoms initially described, there's too much water on the
outside--you're basement is acting essentially as a concrete boat hull.

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