Crawl Space Encapsulation
Encapsulation turns a damp, vented crawl space into a sealed, dry one. The floor and foundation walls are lined with a heavy reinforced liner, the vents and rim joist gaps are sealed, and humidity is controlled with a dehumidifier or a small supply of conditioned air. Done right, the crawl space stays below the moisture levels that support mold and rot all year.
When encapsulation makes sense
- The crawl space has a persistent musty smell that a new vapor barrier alone did not fix
- Framing moisture readings stay high through summer, not just in winter
- There is visible mold growth or staining on joists and subfloor
- Ductwork or the furnace is in the crawl space
- Someone in the house has allergies or asthma and the floor is above an unhealthy space
- You plan to keep the house long term and want the crawl space to stop being a recurring problem
When it is overkill
- The crawl space is dry, framing reads normal and the only issue is a torn barrier
- The house is being sold soon and the buyer's main concern is a single defect
- There is ongoing water intrusion that has not been dealt with yet — water comes first
What a full encapsulation includes
| Component | Purpose |
|---|---|
| Debris and old barrier removal | Clean substrate for the liner |
| 20-mil reinforced liner on the floor | Durable vapor control that tolerates foot traffic |
| Liner up the foundation walls | Stops moisture and air from the walls |
| Taped seams and sealed piers | Continuous vapor barrier |
| Mechanically fastened termination | Liner stays attached to the wall |
| Sealed foundation vents | Stops humid outdoor air from entering |
| Rim joist sealing and insulation | Closes the most common air leak |
| Sealed, insulated access door | Keeps the space closed |
| Dehumidifier with condensate drain, or conditioned-air supply | Active humidity control |
| Humidity monitor | Lets you check conditions without crawling in |
Dehumidifier or conditioned air?
Building code allows several ways to control humidity in an unvented crawl space. The two we use most:
- Crawl space dehumidifier. A dedicated unit sized for the space, with a condensate line drained to a pump or the outside. Works regardless of your HVAC system. Running cost is modest.
- Conditioned-air supply. A small, dampered supply from your forced-air system, plus a return path. Works well when ducts are already in the crawl space. Needs an HVAC contractor.
We recommend one based on your system, the crawl space volume and what the moisture readings say.
Insulation in an encapsulated crawl space
Once a crawl space is sealed, insulation usually moves from the floor above to the foundation walls, which makes the crawl space part of the house's conditioned volume. Fiberglass between floor joists is often removed. Some homes keep floor insulation for comfort; we will explain the trade-off for your house.
Encapsulation pricing by crawl space size
| Crawl space area | Full encapsulation with dehumidifier |
|---|---|
| Under 900 sq ft | $9,000 – $13,000 |
| 900 – 1,400 sq ft | $11,500 – $17,000 |
| 1,400 – 2,000 sq ft | $14,500 – $22,000 |
Drainage, mold treatment on framing and removal of old floor insulation are priced as separate lines so you can see each one.
Encapsulation questions
Do I need to keep the vents open in summer?
No. Once a crawl space is encapsulated, the vents stay closed all year. Opening them lets in humid air that condenses on cool surfaces, which defeats the system.
How much does the dehumidifier cost to run?
It depends on the unit, the size of the space and how much moisture the house releases. A well-sealed crawl space needs little dehumidification after the first season. The humidity monitor shows how often it runs.
Will encapsulation stop water from coming in?
No. Encapsulation controls vapor and air. If liquid water enters the crawl space, it needs drainage and a sump pump under the liner.
Does it help with radon?
A sealed liner reduces some soil gas entry. Radon mitigation is its own system with a vent pipe and fan. If you have tested high for radon, tell us and we will plan the liner so a mitigation system can be added.