Out of sight is out of mind, yet these overlooked areas have a huge impact on the quality of air in a home.  Due to some basic physics and a phenomenon called “the stack effect”, hot air rising through the structure draws cool air into the home from the crawlspace.  It is estimated that as much as 30% of a home’s indoor air comes from the dusty, and often odiferous crawlspace.  If your home has a crawlspace, it should be designed for easy access for regular inspection and maintenance.  If you are building a new home, make sure the crawlspace is designed to be well lit, dry, and easily accessed in order to keep it clean, and free of debris and dirt.  It should also be covered with a wall-to-wall sealed vapor barrier.  If your basement is finished, exterior water proofing, insulation, and drainage systems are much needed features that should be considered as well.