Closed. All year. The old advice to open vents in summer made sense for older houses — but with an HVAC system under the house, open vents feed the humidity problem instead of fixing it.

A real encapsulation has four parts — walls-and-piers barrier, floor barrier, a properly sized dehumidifier, and circulation fans. Here's what encapsulation is, what it isn't, and how to tell what you actually have.