Keeping crawlspace moisture down in the southeast

[Jordan L.]

Hi everyone, I am working on a rehab-to-rent in North Carolina that has some crawlspace moisture and wood rot issues. I'm going to end up replacing 30+ floor joists in this property. Having a repair of this magnitude done is a first for me-- this will be my second rental. This being said, I've done some research online to determine how I can protect myself from having to repeat this repair in the future. My first question is: Are there any other resources I can utilize to educate myself other than browsing the Internet? Here is what I have been told by another investor as to what I need to do after I make the repair to keep moisture levels down. Is this accurate? As of right now, my contractor is going to install a vapor area and call it a day after making the repairs. Would just a vapor barrier suffice or should I do all of this? My only hang up is that... lesson learned... I under estimated repair costs and overpaid a little bit for the property. Of course, I am trying to keep rehab costs down but I will keep the property indefinitely as a rental and don't want to continue to have moisture problems in the crawl. • install a vapor barrier with a minimum of 12 mm thickness • paint the inside of the crawl brick with dry lock paint •install a dehumidifier and sump pump • insulate the floor as there is no floor insulation currently in the crawlspace (how necessary is this?) Finally, should I permit this work? I didn't have to get any permits for my other rehab property... do they slow things down a great deal? Thank you all in advance! Jordan

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@Jordan L.

Included is a photo of a crawlspace detail. This image comes from the book "The Visual Handbook of Building and Remodeling, Third Edition" by Charlie Wing (available on amazon and other places I'm sure) (The Taunton Press, 2009, Newton CT) It's a great book which I'm sure can answer your question regarding more research. 

To answer your question: Yes, the vapor retarder will stop most moisture from the ground from destroying your joists and rotting them out. In addition, it will stop Radon Gas from rising up from the ground and into your living spaces as well, especially if you don't have a pipe + fan assembly for that already installed. 

Insulating the floor space (underneath the joists, with rigid or batt insulation- not shown in this drawing) will keep your living spaces warm during the winter, which given your climate is not so important probably. The insulation itself might have a vapor/moisture barrier attached, but if you have the vapor barrier on the floor already, it won't matter all that much anyway. Insulating the side of the foundation as is shown in this drawing (which may not be 100% of what you have, but illustrates the point) is also a temperature control strategy. You might have a "vented crawlspace" (though given the issue you have, you probably don't) so talk to your GC to find out. A vented crawlspace allows the air and moisture that comes from the ground to escape out through the foundation walls, and thus the moist air doesn't damage your joists. In your case, it's possible that the vents are blocked (with leaves, dirt, etc) and that's why you have the damage you have. 

A super bonus point, which would be expensive, and probably overkill, is to put in the drainage system you see near the footing of the foundation wall (labeled-4" perforated drainpipe). This pipe would be around the perimeter of the house and empty into the storm sewer. Basically, as long as it's lower than the level of the crawlspace, the water in the ground will drain into this pipe, keeping the crawlspace dry, and eliminating your moisture problems. It's on the outside of the footing for easier installation, because the ground on that side is more moist, and because moisture does travel through concrete and into the crawlspace. 

A dehumidifier and sump-pump are overkill in this case. 

Since you are replacing the joists (a structural element) you will most likely need to get a permit. Your GC can help you with this, it will probably cost around $100 or so, will take a week or perhaps two to get, and will require that your GC be licensed and bonded and all that type of stuff. Check your municipality's website for more details. 

Good luck with your project! Sorry about the unexpected surprise.