The better question is “What Moisture Content in wood does wood start to noticably decay” and thats 20%
In my 15 years of inspecting over 3000++ crawl spaces I have found I only see mold growing on the wood floor structure, ceiling in the crawlspace, when the wood moisture content is 16% or above. Some “experts” even say 15%. All NC Open Foundation Vented crawlspaces have humidity over 80% starting from May 15th. That means the Wood Moisture content of the Wood is over 16%… which is now enabled to grow mold. And this warm humid season lasts through October 15th. Thats a good 5 months where your floor system is probably getting weakened, each year, slowly, consistantly. Until 20 years later the 3rd owner upon Buyers Inspections see’s the report of Mold Found Throughout crawlspace wood menmbers. And now the Buyer wants a new AC, New AC Ducts, new carpets, UV light in AC, and a HEPA scrubber in the home for 5 days…yadda, yadda, yadda.
MOLD ONLY COMES FROM DIRT!!!!!!
Uv light in sunlight kills most of the surface mold on the planet. But when a tree falls down in the forest and sunlight ca’t reach underneath it…mold thrives and eats away at the fallen tree from the bottom up. In outr crawl spaces THERE IS NO SUNLIGHT with UV Light….but covering the ground with plastic starves the ground od oxygen and mold finds it hard to thrive. If it does colonate it can’t get past the plastic. So:
THE FIRST RULE IN CRAWL SPACES IS:
100% Plastic down drastically reduces mold spores in the air. It doesn’t stop mold from growing on you wood floor structure, it just delays it considerably.
But!!! I have seen ceilings in crawl spaces of newly constructed homes and they sweat and condisate considerably and within 45 days of the closing on the new home the entire crawl space ceiling was growing mold.
2nd thing ALL NC RESIDENTS SHOULD DO upon purchasing a home with a crawl space.
A. Air seal and insulate the foundation vents, this costs a DIYer $30. But now stops 2 Good Year Blimps of moldy, warm, moist air from rising through the average 2400 sf home.
B. 2nd thing to do is air seal the crawl space door so it hold air. Like your front door of your home, you can easily come in and out, but theres a rubber strip that seals out the air flow.
C. Have you AC, which automatically makes 50% humidity air, trickle into your crawl space 1/10th of 1% of the AC air, as lightly as you can blow on your hand, for 90-seconds each hour, and your crawl space stays dry, mold/critter free for the life of the home.
D. Cover 100% of the ground with plastic…does HAVE to be perfectly flat (flat against ground makes it work better)..smooth…just cover it so it starves the ground of oxygen.
Benefits:
I. 18%-22% Better Energy Efficiency.
(We put Emporia: Whole home electricity monitors on over a dozen homes) and found with our IntelliHushFan drying sytem we can claim 18%-22%. Thats $36-$60 a month back in your pocket. Dehumidifiers in crawl spaces that are sealed eat up $45-$55++ in energy each month. So you’ll NEVER hear a professional sealed crawlspace video on ENERGY SAVINGS : ) But when you replace the dehumidifier every 3-5 years they profit $1,000-$2,000 on the $2800 – $5,000 install. Buyer Beware.
2. GREAT AIR QUALITY!!!!
Since the mold is wiped from the crawl space wood ceilingand the ground, where mold comes from, is 100% covered then the mold spores in the air are JUST ABOUT eliminated. To be sure 99.99% install a UV liught inside your AC system or your return in your first floor. A UV Light kills 99.99% of germs, viruses, allergies, molds, bacteria…etc. Anything airborn and biological it kills. Its like you and I going to the tanning bed for 10 hours. Were going to pass away. And that’s how a UV Light in your AC works. Wholesale…$50 ish
3. AC Lasts 20%-25% Longer:
If AC is in crawl space, which is now dry and condensation free. New AC’s are $8,000-$14,000.
4. Hardwood floors stop cupping.
Hardwood floors cup because the wood inside the living area is at 50% humidity, like the rest of the living area in the house, because of the 50% humidity AC. But the open foundation vent crawl space is sweating and condensating on everything in the crawl that’s colder than 80F. WHICH IS EVERYTHING especially Metal AC housing , plastic outter wrapping insulated ducts, shower and toilet pipes. Condensation line from AC dripping cold water dripping off the condensation lines in the crawl space.
Making the crawl space air under 76% Humidity stops colder floor boards from sweating. 72% and below better…50% humidity WAY OVER KILL but every company tring to sell you a dehumidifier will say differently. Ask them: at what air moisture % does wood in crawl space become 16% wood moisture content. If they say 80% there correct. So technically anything under 80% humidity in crawl space will make the wood moisture content under 16%. YES…and NO. I still find sealed crawl spaces at 76% humidity and above will have AC condensate. But the Supply air from the dry 50% AC is keeping the air dryer and evaporating the condensating moisture on the metal AC. So, at 76% humidity cold surfaces like the metal AC box sweats and condensated and drips, BUT, the air supply keeps the air dry enough to evaporate it. So moisture is higher, but optimally you want it 72% humidity and below. Allowing it in heavy rains, hurricanes…to pop above 75% for a few hours, then after rain the crawl space dries out again. This happening a couple times a year won’t make a dent in anythiong
Once humidity in crawl space is lowered under 76% the wood floor underneath will no longer condensate and boards dry out. Now, 2 sides of the board are dry and NO CUPPING. Its when the bottom of the hardwood floors sitting on wet condensating plywood floor boards, the bottoms of the hardwoods swell with moisture and top is dry so the board starts to cup.
4. Far Less to None Critters:
Cockroaches eat mold in crawl spaces and then come into home mostly around AC register that are not foam sealed from underneath. No mold=no cockroaches.
5. NO INSULATION OUT OF PLACE
Insulation in crawl space ceiling ONLY move out of place because snakes hunting mice. I have seen DRIPPING WET insulation from a hot water pipe leak and NO INSULATION was out of place. I have seen dry dry crawlspace insulation where its all hanging down like a Hauted House Event. Snakes hunt mice in NC in the crawl space insulation. Mice eat camel crickets and cockroaches that eat mold. Get humidity down, wipe as much mold away, dry crawl spaces, as stated above, and your insulation ALWAYS stays in place and gives you best energy efficiency.