What is an acceptable level of humidity?  Do I really need a moisture barrier aka vapor barrier in my crawl space?  These are common questions that are posed to a home owner and potential home buyer when faced with inspections.  These issues usually arise from a termite inspection that is geared to up-sell a potential home owner or home seller on a product that may or may not be necessary and these typically come with a high price tag to the consumer. 

Let’s look at a couple of different things.  The first thing we need to consider is what is an acceptable level of humidity in your crawl space?  The second thing to consider is what do the hygrometer’s actually tell you when they pull out their meter readings?  The third consideration is what can be done to help alleviate a crawl space with a high humidity level?

“This is what you need to know.  A hygrometer measures relative humidity.  Your crawl space humidity should be under 55%.  Maintaining a safe crawl space humidity level means maintaining a humidity level below 55%.  Keeping your home’s crawl space humidity level under 55% prevents mold and mildew from growing and hinders dust mite invasion.” JES Foundation Repair

The most common home building technique used in Arkansas is a vented crawl space foundation.  This can lead to a variety of questions and concerns regarding pest infestation, mold, fungi, dust mites, sinking floors, wood rot, etc.  All these issues come into consideration when there is a high humidity level in your crawl space.  There’s not one home owner or potential home buyer that wouldn’t run for the hills when presented with the notion that your home’s foundation could rot right out from under you.  What should you do? 

Have a professional come out and examine your crawl space.  There are many crawl space foundation repair companies that are in Arkansas and you have probably seen their ads that will provide you with a free inspection and estimate.  Just remember that anytime you see “free inspection and estimate” that this means you will most likely be quoted the “high” end treatment and resolution to problems that you may not have currently, or you may never have.  Keep this in the back of your mind; when you are a hammer; everything is a nail.

This is just my opinion, but I would leave the termites to the termite experts and the crawl space/foundation to a disinterested third party, like an engineer. 

I have been in the pest control industry and worked for the major players and trust me; I wouldn’t want someone diagnosing my crawl space who was just handed a hygrometer, an iPad, trained by watching videos with an incentive on paid commission. 

This doesn’t mean that you need to spend thousands of dollars to have your crawl space at an acceptable level of humidity to prevent these issues.  A lot of these issues can be resolved by a moisture barrier aka vapor barrier.  In extreme circumstances you may need to encapsulate your crawl space.  Again, please let a professional (engineer) examine your crawl space before committing to a high dollar solution that could have been resolved with a moisture barrier. 


A moisture barrier resolves and prevents problems such as:

  • Pests and rodents
  • Excess moisture
  • Foundation sinking
  • Bowing
  • Mold and other toxins
  • Radon gas


A moisture barrier can cost anywhere between .50 to .75 cents per square foot.  It is a plastic sheet that lines the ground and wall of a crawl space to restrict moisture from entering.  Prices can vary depending on the thickness of the moisture barrier.  This can range from 6 millimeters to 23 millimeters.  The rougher your terrain the higher you may want your thickness to prevent tears. 

For you DIY’s, yes, you can do this on your own.  I just did a google search and found 4 videos at a glance with step by step guides from measuring to application.  One thing to keep in mind is that you will get dirty! 

However, if you feel you have an issue with high moisture then I would recommend calling in a professional to make sure that you don’t need to clean out your crawl space first from any potential mold or mildew that may have occurred before installation. 

For the science behind moisture control, vapor barriers, humidity levels in crawl spaces and encapsulating your crawl space foundation I encourage you to do your own research and make an educated decision based on your home’s needs.  http://crawlspacescience.com/