There are several reasons why you should consider installing a basement vapor barrier after you have added insulation in a room. Protective sheeting over the basement floor helps prevent moisture from penetrating the walls, and will inhibit mold and mildew from propagating, damaging your walls. A vapor barrier’s plastic sheeting will stop the walls from becoming damp, which will stop moisture from rising to the rest of the house, wreaking havoc and warping floorboards. However, you may experience issues fitting the barrier if you have multiple electrical outlets, ducts, or other connections. Many homeowners think they can avoid this by installing insulation with a pre-built vapor barrier included, but many put the barrier so that it faces upwards, instead of pointing it downwards so it effectively protects your basement. In short, you should install a vapor barrier if your basement often becomes saturated because the water table is above the foundation, but it can be difficult and costly. However, these short-term costs will negate the much larger cost of replacing supports and insulation in your basement after moisture penetration.