My husand and I are building a house on our own and a question my husband has is how do you vent a crawlspace?

You do it with louvers located within three feet of each corner of the crawl space, and enough of them to give a net free area of one square foot for each 150 square feet of crawl space floor area. If an approved vapor retarder material is provided on the ground surface of the crawl space, the net free area of ventilation may be reduced to 1/1500 of the total crawl space floor area, BUT you may want more ventilation for other reasons, such as radon gas mitigation.

Despite old-wives tales and some vent manufacturers' recommendations, the vents should remain open AT ALL TIMES, and ESPECIALLY in winter.

here in coastal south carolina - very hot and humid - do we also need to leave the crawlspace louvers always open?

i bought a home with electric crawlspace fans, full moisture barrier and evidence of standing water problems in low spots (clay subsoil)..all of which appear to be functioning fine amidst the current drought.

If the crawl space is not "conditioned", meaning heated or heated and cooled, then the vents are required, and the purpose of leaving them open is to allow moisture which accumulates on very humid days to migrate back out of the crawl space on less humid days,

If you close the vents, and the crawl space is not totally sealed, moisture will collect, both from the outside air and from moisture-producing activities in the house, leading to possible mold problems and rotting of wood structural members. I personally don't believe a TOTALLY 100% sealed crawl space can be built, and even if it could, I doubt that it can be maintained 100% sealed over time.

Vents open is the best policy, assuming of course that the floor above the crawl space is well insulated.