Sealed Crawlspace in Action To the Editor: I have been battling with a local building department over the issue of ventilation in crawlspaces (see "Crawlspace Ventilation Update," 8/99; Letters, 10/99, 1/00). I say it's best to seal it up and of course they say ventilate it. Two years ago, I built a family-room addition and made the 22x14-foot 3- foot-high crawlspace to serve as a storage area for outdoor items, accessible with a hinged door from outside. I used a 6-mil poly vapor barrier under the slab, and insulated the joist bays with 1- inch-thick R-board and 9-inch (R-30) fiberglass fit between the joists, and another layer of the R-board on the underside of the joists, with the