Crawl Space Encapsulation Cost (Moisture Control)

A basic 6-mil poly vapor barrier laid over dirt is the cheapest version of encapsulation and does little beyond blocking direct ground moisture. A full encapsulation using 12-20 mil reinforced liner sealed at the walls and piers, combined with sealed foundation vents, closes off humid outside air entirely, which is what actually stops the cycle that grows mold on joists. Pricing jumps significantly between these two tiers, and a quote that doesn't specify mil thickness and whether seams and piers are sealed is hard to compare against a competitor's number.

An encapsulated crawl space still needs a dedicated dehumidifier sized for the space, running more or less continuously, since sealing out ground moisture doesn't address humidity already trapped inside once vents are closed. This adds both an equipment cost and a modest ongoing electricity cost that a homeowner comparing bids should ask about, because a low encapsulation bid that omits a dehumidifier is not actually solving the mold-prevention problem it's being sold to solve.

If mold is already present on floor joists or subfloor, that gets remediated first, since sealing a vapor barrier over active mold growth just traps it in place. Expect this as a separate line item priced by square footage of affected joist area, quoted alongside but distinct from the encapsulation materials and labor.