I bought a 1927 house last year and, afterwards learned I'm especially sensitive to mold and this house has plenty of it. I've eliminated mold everywhere I've found it except in the inaccessible crawlspace under a kitchen and bedroom addition (1960s? 70s?). I've fixed leaks and replaced drywall, ductwork, etc but I can still smell mold coming up from the crawlspace, which has no access panel but several vents. The height ranges from about 10 inches under the kitchen (worst mold area) to 2 feet at one bedroom corner. I don't know how to get rid of the mold under the addition: seal it and find a way to keep it dehumidified? pay someone to spray foam underneath? install ultraviolet lamps somehow to kill the mold? Help!

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    There are foggers that disperse a fine mist of mold killing chemicals. Mold bomb aerosol cans might be a cheap method to try in the crawl space. Be aware that even after a successful kill off of mold under the home you will have to address ventilation and humidity control to keep the mold from coming back. – Kris Nov 4 '19 at 13:54
  • Kris this should be an answer , I was going to post the same. – Ed Beal Nov 4 '19 at 14:23
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    My solution would involve making an inaccessible crawl space accesssible. (It may already have access that you're unaware of.) There are many reasons to want access to your floor framing. Let us know if that's a possibility and I'll write an answer. – isherwood Nov 4 '19 at 18:10
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    i would puff a bunch of boric acid down there, the stuff in squeezable bottles that they sell to kill roaches and ants. It's a cheap and very powerful anti-fungal agent, it's a fire-retardant as well, and it's safe to use around people and pets. If that $5 solution didn't handle it, call in a pro or bomb it as above. – dandavis Nov 4 '19 at 18:24
  • Just a note; it would likely be a building code violation to seal up your crawl space and most likely would make your situation WORSE! Mold grows with moisture. If you have excess moisture under your house, that is the thing that needs fixing (after the other suggestions of getting rid of the immediate problem). It will not be inexpensive (french drains? excavation?). – JRaef Nov 4 '19 at 20:59

After killing the existing mould. Ventilation is the answer (usually).

I'm rebuilding a stone wall/underpinning in a large underfloor area (appx. 1.7m high or nearly head height) and it had a serious mould problem a couple of years ago. The guys came in, cleared out a load of old mould infested rubbish and then installed an air pump with a series of metal ventilation ducts with rubber outlets.

The system measures humidity and temperature and then draws in air from outside and pumps it through the ducts into the whole basement. I think they aim for 50 to 60% humidity and around 10 to 12 degrees C down there.

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