Moisture Issues

• If you find issues with moisture on or near your basement walls, such as leaks, dampness or blistering paint, a vapor barrier will go a long way toward correcting the issue. Install a vapor barrier not only to protect moisture from damaging the insulation, but also to prevent water damage to the wall.
  
  

Cellulose Insulation

• If your walls already have cellulose insulation in them, you do not need a vapor barrier. The back wicking of cellulose insulation resists airflow, which prevents moisture from accumulating and protects against damage. This does not apply to refrigerated rooms or rooms with indoor pools.
  
  

Bottom Line

• Always install a vapor barrier at least on exterior house walls, including basements. It will cost you a lot less money to install a vapor barrier than to repair moisture damage. Many insulation materials have a vapor barrier applied on one side for easier installation.