Crawlspace needs better ventilation?

Question

Hello All, I purchased a rental 2 months ago and the inspector noted that I needed to improve the ventilation in the crawl space. He noted there were slight indications of mold growth. I have now received 2 quotes from different people to fix the issue. One person (aqua guard) suggested closing it off completely and the cost to do this is over 7 grand. The second person proposed closing off several openings and putting a fan in one end of the crawlspace to pull moisture out. This quote included a new vapor barrier and came out to just under 5 grand. I am located in Georgia so we have cold winters and very warm/humid summers. Does anyone have guidance on cheaper solutions?

Mike McCarthy · Answer

There’s a movement in home building to eliminate crawl space vents and instead make the crawl space ‘part of the house’. It’s a solid concept and highly recommended in more humid climates. If it’s 60-70% humidity outside, what is the humidity inside if you add vents and circulate the air... the same high humidity.

BUT, you can probably do a similar job to some of these basement companies for a lot less. I find they are horribly overpriced for the materials and time required.

Nathan Gesner · Answer

You can cut vents into the walls and the natural airflow should be sufficient to dry it out. I would probably put a strong blower fan down there for a few days or a week just to dry things out at first but see no reason why you would need a fan down there permanently.

I'm in a cold climate so my vents have to be closed in the winter or pipes can freeze.

Chris London · Answer

@Max Rieves 80% refers to the amount of ground that is covered. So 80% of the ground is covered by a vapor barrier and 20% is just the dirt. I've had different people tell me different amounts from 80 to 90 to 100% covered to encapsulation (which usually goes up the wall also).

You can buy vapor barrier in rolls at Home Depot and just roll it out yourself.

I don't know anything in regards to thickness however, sorry.

-CL

Mitch Harold · Answer

i tend to think more ventilation is better than less.  We put lattice around a crawlspace to let it breathe and keep most critters out.  If you close it off, the moisture from the ground has nowhere to go and will most likely be absorbed by subflooring.  Im in south louisiana with high humidity.  In my opinon, every part of your house needs to breathe.

Jesse Clark · Answer

I would go with encapsulating, closing off vents. Crawlspace vents are a terrible, outdated part of building code that hasn't changed forever. As Mike M mentioned, when there's high humidity outside that air is coming under your house, and then contacting cooler surfaces in the crawlspace. It's a recipe for disaster. I'm in Maryland, often have very humid summers. I've seen many vented crawlspaces that are moldy, damp. Dryest ones I've been in are closed up, some have dehumidifier in them. Think of the crawlspace as a really short basement, you want it to be part of your house, not open to drastic exterior temperature changes.

Steve Morris · Answer

In any case, I'd recommend doing this sooner rather than later - Moisture invasion repairs get more expensive the longer you wait.

The idea of sealing off a space that has moisture in it sounds sketchy, I'd opt for the good ventilation.  In addition, remedy the existing mold and make sure you have a moisture barrier on the dirt to minimize that source.

Max Rieves · Answer

@Chris London thanks Chris! I already have the home services for termites and there is a vapor barrier down. What is a 80% vapor barrier? The 2nd quote I got was for a new and thicker vapor barrier Bc the exhaust fan was going to deteriorate the older/thinner barrier that I currently have.

Theresa Harris · Answer

Why not put a vent on it like people have on the front of their house near the peak?  You can always add a dehumidifier.  If moisture is coming up through the ground, line it with plastic.

Chris London · Answer

@Max Rieves I'm just north of you in Raleigh and it's not just the mold (which is a big deal) but the moisture also attracts termites. While my crawlspace stays pretty dry with just 80% vapor barrier, my neighbors was always damp until he encapsulated it. A dehumidifier is a cost-effective way to go but keep in mind, a dehumidifier won't' remediate the mold that is already there. If you didn't get a pest inspection to check for termites you might look into that. I pay the $125 annual fee to have them come back and inspect every year.

I'm not an expert but maybe start by 1) termite inspection 2) remediate the mold 3)80% vapor barrier 4) Keep an eye on it 5) add a dehumidifier if necessary 6) consider encapsulation.

Crawlspace needs better ventilation?

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