Foundation Venting Cutting holes through foundations is bad. It doesn't matter if the foundation is short and encloses a crawl space or fully excavated for a basement. In any season, in any climate, foundation venting offers no benefit to the building.   Venting is offered, and even required in some areas, as a method of preserving the floor system over crawl spaces. Generally, the real effect is higher moisture content in the woodwork and higher heating and cooling costs. In the heating season, vents flood the cellar and then living areas with cold air. Cold air flowing through the vents is ineffective at evaporating foundation moisture. Of course, very active venting could freeze the soil and this would suppress the enclosed water vapor and biological activity. It would be hard on the plumbing and make barefoot walking on the floor above difficult. During warm weather, the ambient air is loaded with water. When this air is drawn into a cool space, the entrained water vapor must condense. And it must wet all the available surfaces-the foundation, the soil or masonry floor below, and the wooden suspended floor above. For example, if 80 degree, 50%RH air is allowed to vent into a 60 degree crawl space, the air will saturate and indoor rain will result. This grows fungi wildly which is terrible for the health of the building and its occupants. Soaking the wooden building components adjacent to the foundation invites larger bugs as well. After some time, the space becomes a zoo leading to real structural and indoor air quality problems. We all want our homes to be healthy, durable, comfortable, and economical places to live. Foundation venting will not promote any of those aims. Back | Next