A complete encapsulation includes mold remediation if needed, closed-cell foam at the crawl walls and rim joist, a 20-mil polyethylene vapor liner sealed at the perimeter and seams, dehumidifier or supply-air mechanical conditioning, and access closure. Typical cost: $4,500-$12,000 for a 1,500-2,500 sqft crawl space.
More detail
Crawl space encapsulation is the bundling of multiple distinct trades into one project. The typical scope sequence in Cincinnati. (1) Initial assessment: moisture meter readings on the framing, identification of mold or rot, evaluation of existing vapor barrier (often a tattered 6-mil sheet that should be replaced), check for active water sources (leaking foundation walls, plumbing leaks, condensation on cold pipes). (2) Mold remediation if applicable: typically handled by a separate mold remediation contractor under containment; cost $1,500-$5,000 depending on extent. The encapsulation project waits until mold remediation is complete. (3) Closed-cell foam at the crawl walls and rim joist: 2-3 inches typical. The foam isolates the crawl envelope from the surrounding soil and air-seals the rim-joist band. Cost: $1,800-$5,000 depending on perimeter linear footage. (4) Heavy-duty polyethylene liner installation: 20-mil thickness is the Cincinnati standard. The liner covers the dirt or rock crawl floor, runs up the foamed walls 6-12 inches, and is sealed to the wall with mechanical fasteners and butyl tape. Seams are overlapped and sealed. Penetrations (plumbing, electrical, HVAC ducts) are detailed with custom-cut boots. Cost: $1,500-$3,500 depending on square footage. (5) Mechanical conditioning: a small dehumidifier (Aprilaire, Santa Fe, or similar at $1,200-$2,500 plus install) maintains the encapsulated crawl at 45-55 percent RH year-round. Alternative: a supply-air feed from the main HVAC system provides modest conditioning at lower cost ($300-$800 install) but with less precise humidity control. Most Cincinnati installers recommend the dedicated dehumidifier for any encapsulation in the $7,000+ range. (6) Access closure: a sealed and insulated access hatch replaces the typical leaky access cover. Cost: $200-$500. Post-install verification: humidity reading 60 days after install should be consistently below 60 percent RH; framing moisture content should be below 19 percent. The full project on a typical 2,000 sqft Cincinnati crawl space runs $6,000-$10,000 with the dehumidifier included.