Does Your Home Have a Crawlspace?
If you live in North Carolina you typically have three choices as to what type of foundation your home will have. You will either have a crawlspace, a basement, or your home will be on a slab....which is a slab/bed of concrete. In general, the basement home is the most expensive and requires a certain slope of the lot in order to permit the home and have a solid structure. A slab home is usually less expensive and there will be no access under the home itself. Most homes in North Carolina will have crawlspace. This is as it sounds...you will have a little room to "crawl" under the floor level of the home and this is where you will find HVAC ducts, wiring, etc. Sometimes, depending on the slope of your lot, you will have a walk-in crawlspace....which, is as it sounds, you can stand up and walk under your house.
Moisture and Humidity Levels
If you do have a crawlspace it is very important to monitor the moisture and humidity levels. There are various reasons as to why the levels may fluctuate and even more opinions on ways to control the levels. This post is a general rule of thumb snapshot and if you are to take action you should seek advice from a qualified crawlspace contractor. With that said, your moisture levels should be around 14% or less....no more than 20%. Your humidity levels should be around 50-55%. These levels can be read by simple instruments you can buy at most hardware/big box stores.
If Your Crawlspace Has High Levels
If you do have higher levels in your crawlspace, depending on it's severity, there are several things you can do to control them. A simple thing to do is to lay a 6-10 mill vapor barrier on the ground and have it cover 100% of the floor of the crawlspace. This will keep the moisture under the plastic barrier. Going a step further, the old school of thought is to open your vents from April to October and close them from November to March. These theories are changing over time and what I am seeing a lot these days are totally sealing the crawlspace.
Types of Sealed Crawlspaces
For the sake of general information, there are two types of sealed crawlspaces; the first is a total seal. This basically means that the crawlspace is covered in a vapor barrier not only on the ground, but also on the sides of the crawlspace totally encapsulating the area. The piers are wrapped, vents are sealed, and a dehumidifier is installed along with removing insulation under the sub floor. An alternative to the dehumidifier is tapping into an air duct and having the space "conditioned" just like the livable area of the home.
A less expensive alternative is placing the vapor barrier on 100% of the ground, sealing the vents and installing a dehumidifier. This does almost the same thing as a totally encapsulated crawlspace, just not as "complete". A lot of new construction of the higher end homes are sealing crawlspaces with one of the methods mentioned.
My home is 25 years old and the previous owner had a sump pump installed as it had accumulated water from heavy rains. There was no real detriment to my home, but my crawlspace levels were high which was leading to my hardwood floors cupping over time. Mine was not extreme, but I could tell it was happening so I took action. Prior to taking action my moisture levels were around 18% and the humidity levels were around 80% plus. I took the less expensive route and had a new vapor barrier laid down, sealed the vents and installed a dehumidifier. Four days later my humidity level was around 58% and moisture level was 14% going down. I can tell not only do my hardwoods "seem" to be flatter, but also, not that there was a stitch in the air, but it seems the air quality (smell and efficiency of HVAC) improved. A semi sealed crawlspace is probably going to be around $2-3K and a full encapsulation is around $5-9K. Below are pictures of a totally encapsulated crawlspace, a dehumidifier, and mild to moderate cupping of hardwoods.