Tiny crawl space ventilation – GreenBuildingAdvisor

Help me weigh options here.

Looking at a crawl space for a 20 year old small addition. It was constructed difficult to access but was recently found to be very problematic during a mold investigation.

It is 10×5 x 4 feet deep. It was not vented to the exterior nor was it vented to the interior adjacent full basement.

Recent inspection shows high humidity (66% in March Zone 4A) and actual mushrooms growing on one piece of framing.

A company is coming in to remediate in a few weeks and I’m looking at post remediation fixes.

Already planning on addressing exterior ground drainage and doing an interior encapsulation with Stego system. Will insulate the rim joist with mineral wool.

My question is how to ventilate the space into the adjacent basement.

Option 1. Passive

Cut 2’x3’ ‘window’ through concrete foundation wall and rely on air movement in basement. Most expensive option.

Option 2. Active

Core 2 6” holes through foundation wall at each end of space at mid height of wall, install inline duct booster fan in one hole to push air into space.

Option 3. Active

Cut 2 4” holes through rim joist and each end of space and install inline duct booster fan to push air into space.