We build homes in the United States differently in every local. This is primarily due to geographic concerns. For instance, many homes in the North have basements. This is not the case in the South where high water tables can make basements problematic. There are millions of homes built from Northern Florida to Ohio and Indiana that are built over crawl spaces.
Crawl spaces are an important and often misunderstood area of the home that can cause issues for a homeowner. Moisture, the number one concern in these areas, can attribute to high humidity, mold growth, and buckled hardwood flooring. Understanding how to deal with moisture can be further complicated by various crawl space ventilation and insulation techniques used.
Traditionally, homes in this region were built on posts or piers. Although not constructed optimally from an insulation perspective, the under floor area was perfectly vented and the ground temperature followed the ambient outside air temperature. As time moved on, we learned that crawl space temperatures follow seasonal temperatures. They are not as cool in the winter or warm in the summer as post or pier construction therefore heating and cooling costs can be reduced. Thus, crawl spaces became more common.
To ensure crawl spaces still behaved like post and pier buildings, crawl space ventilation became a code mandate in the 1950s. The basis for the code requirement was two-fold; that the primary source of crawl space moisture was evaporation from the ground, and that crawlspace ventilation would allow this moisture to escape. Eventually, we moved away from this code. After time, no significant evidence was available to support the mandate.
Today, many crawl spaces are closed. With the widespread use of air conditioning, most crawl spaces are now non-vented, especially in the East. The disparity of hot, humid outside air contacting interior cooled air is a recipe for condensation. The basic approach is simple.
Polyethylene ground sheets are now widely used as they inhibit evaporation from the crawlspace floor. Fiberglass insulation, which has proven to be ineffective in moisture prone areas, is being replaced with reflective insulation. Reflective insulation is not affected my moisture and its use under floor has two benefits. The first is the construction of the insulation. Because the insulation consists of reflective aluminum and polyethylene it cannot absorb moisture. The second benefit is its heat blocking ability that keeps inside heat in during the winter and out during the summer.
Coupled with a groundsheet and insulation, it is also vitally important to keep bulk water out of crawl spaces. Site grading is generally the most important consideration as drainage from pavement and roofs are a potentially huge water source. Paying attention to any plumbing maintenance is also critical.
The decision to seal or not depends largely on your climate. Identifying the various complexities involved in your specific house and paying attention to your climate and geography will help ensure you have a healthy, problem free crawl space with low moisture and good insulation.