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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
Encapsulation turns a damp, vented crawl space into a sealed, dry part of the house: a heavy liner over the floor and up the walls, the vents closed, the walls insulated and a dehumidifier to keep it dry. Each of those is a separate line on a quote. Enter your crawl space and choices, and this prices every part as a contractor job or DIY.
With these inputs:
| Result | Value |
|---|---|
| Installed encapsulation cost | $4,594 – $9,172 |
| Cost per sq ft of crawl space | $4.59 – $9.17 |
| Liner needed | 1,529 sq ft (2 × 10×100 ft rolls) |
| Liner, installed | $2,294 – $4,587 |
| Wall insulation | $780 – $1,365 |
| Dehumidifier | $1,200 – $2,500 |
| Seal 8 vents | $320 – $720 |
What you are paying for. The liner is the biggest single item: a reinforced polyethylene sheet over the whole floor, lapped and taped at every seam, wrapped around piers and run up the foundation walls to within a few inches of the sill, where it is fastened with a termination bar. Thicker liners cost more but survive being crawled on; 12 mil is the common middle choice and 20 mil is for crawl spaces that get regular traffic or storage. Sealing the space changes how it has to be dried. Once the vents are closed, the crawl space needs either a dedicated dehumidifier or a small supply of conditioned air from the HVAC system, and building codes treat a sealed crawl space as part of the conditioned house — which is why the foundation walls, not the floor above, get the insulation. Water comes first. If water stands on the floor after rain, fix the grading and gutters and add a drain or sump before sealing, or the liner simply traps the problem. Is encapsulation worth it?. In humid climates, a vented crawl space brings damp summer air under the house, where it condenses on cool ducts and framing. Encapsulation keeps the framing dry, stops musty air reaching the living space, and puts ducts that run through the crawl space inside the conditioned envelope. The energy saving is real but usually modest; most owners do it for moisture, mold and comfort. Published 2026 cost guides (Angi, HomeGuide, Forbes Home) put typical full encapsulation at roughly $5,000–$15,000, or about $3–$9 per square foot, with basic liner-only jobs below that and jobs with drainage, mold remediation or structural repair above it. This calculator prices each part so you can see which of those lines is in your quote.
Liner sq ft = (floor area + perimeter × wall height) × 1.10 · Liner = liner sq ft × $1.25–$4.00 installed by thickness (DIY $0.20–$0.80 material) · Wall insulation = perimeter × wall height × $2.00–$4.00 (DIY $1.00–$3.00) · Dehumidifier $1,200–$2,500 · vents $40–$90 each · sump $1,000–$2,500 · cleanup $0.75–$1.50/sq ft · Total = liner + walls + dehumidifier + vents + sump + cleanup
| Crawl space | Contractor | DIY | Per sq ft (pro) |
|---|---|---|---|
| 500 sq ft | $3,193 – $6,388 | $1,598 – $2,654 | $6.39 – $12.78 |
| 800 sq ft | $4,031 – $8,047 | $1,825 – $3,065 | $5.04 – $10.06 |
| 1,000 sq ft | $4,594 – $9,172 | $1,975 – $3,341 | $4.59 – $9.17 |
| 1,200 sq ft | $5,136 – $10,258 | $2,116 – $3,605 | $4.28 – $8.55 |
| 1,500 sq ft | $5,897 – $11,775 | $2,315 – $3,968 | $3.93 – $7.85 |
| 2,000 sq ft | $7,156 – $14,296 | $2,639 – $4,568 | $3.58 – $7.15 |
Perimeter assumes a 1.6:1 rectangle and one vent per 125 sq ft. Computed with this calculator.
In this calculator a 1,000 sq ft crawl space with 3 ft walls, a 12 mil liner, rigid foam on the walls, a dehumidifier and 8 sealed vents costs about $4,600–$9,200 with a contractor, or $4.60–$9.20 per sq ft. Add $1,000–$2,500 for a sump pump if water pools.
About $2,000–$3,300 for the same job DIY: roughly 1,530 sq ft of 12 mil liner, seam tape and fasteners, foam board for 390 sq ft of wall, a crawl space dehumidifier and vent covers. The dehumidifier is the largest single DIY cost.
Code minimum for a vented crawl space is 6 mil, but encapsulation liners are usually 10–20 mil reinforced polyethylene: 12 mil is the common choice, 20 mil if you store things down there or crawl through often.
A sealed crawl space needs a way to remove moisture — either a dehumidifier sized for the space or a small conditioned-air supply from your HVAC system, as the building code allows. Without either, humidity can build up under the liner.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.