We have high levels of water-damage molds in our finished semi-basement (4' below ground). The musty smell came from a ~20' long 4' high 5' deep storage area we'd built into the wall, on a concrete pad floor.

How would you ventilate it, and/or prevent condensation or water vapor coming in?

I'd measured 16-18% moisture in the drywall in the back and a bit elevated moisture in the concrete side wall. We've just had a remediation company remove the 5 sets of roll-out shelves & frames for doors and scrub the cavity, but they found no clear water damage. We're in N. Calif; the basement stays ~68-F even when it's 100 degrees.

We tried leaving one of the wide cabinet doors open for ventilation; that simply made the whole basement musty. In May the basement's ERMI (relative indoor/outdoor moldiness index) was 20.07 Which is seriously bad.

And we have a highly mold-sensitive kid, so we really need to prevent more mold in the future.

What would you advise to prevent future issues?

Design details:

In '09 we'd pushed out our LR 5' beyond the finished semi-basement's footprint. The cabinet framing seen above is below the LR, created from the new footprint. It's a single cavity on slab, (4' above basement's floor), subdivided into 5 "cabinets". The right side wall is composed of primed old concrete blocks (abuts our door landing).

Each "cabinet" was custom, with a front frame, open back and no sides. Each base sits on styrofoam boards on a concrete pad, with a roll-out drawer attached to the base.

We have hydronic floor heating throughout. The low-velocity HVAC air return is nowhere near; 3 half-flights of stairs higher. DH later added a vent into the AV cabinet above, but it doesn't seem to do much except vent the mold somewhat. :-/

It all seemed like a great idea, but not if it's making us sick.