When a home has an unconditioned (unheated) crawl space, most building codes require that there be some form of crawl space ventilation. This comes in various forms but, at least in Bellingham and Whatcom County, more often than not the builders put in foundation vents -- typically a few feet from each corner and spaced quite evenly from one another, every few feet.

The preferred vents are those with wire mesh, typically 1/4" galvanized screens. Often, instead, I will see vent screens like the one below.

This is a louvered vent screen and the average person may not know it, but the louvers seriously impede the "net-free" area. In other words, if the goal is to have some air movement then these are of marginal design. With a few exceptions, I typically suggest that these vents be replaced with proper vents that do not impede venting. There is some controversy in some areas, where inspectors recommend that vents be closed. If a WSDA licensed inspector in this state suggests that, he or she is likely to receive a reprimand. Crawl space vents that are blocked are a state mandated conducive condition. As an inspector, at least in this region, I can say that I never encourage blocked vents. When I inspect older homes with few, or blocked vents, it seems like anobiid beetle infestations are often a part of the equation.

Thanks for stopping by,

Steven L. Smith