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Crawl space encapsulation is the permanent moisture fix after crawl space mold removal. It seals the floor, walls and vents with a heavy liner and adds humidity control.
Encapsulation covers the soil and walls with a 10–20 mil reinforced liner, seals vents and the rim joist, and adds a dehumidifier or conditioned air. Most projects cost $5,000 to $15,000, or about $3 to $8 per square foot.
Vapor Barrier vs. Full Encapsulation
| What is covered | Humidity control | Typical cost | |
|---|---|---|---|
| Basic vapor barrier | Soil floor only, 6–12 mil plastic, loosely laid | None; vents stay open | $1,500 – $4,500 |
| Full encapsulation | Floor and walls, 10–20 mil reinforced liner, seams taped, vents sealed | Dehumidifier or conditioned air | $5,000 – $15,000 |
Either option works best once crawl space water control is in place.
Liner Thickness, Explained
| Liner | Typical use | Notes |
|---|---|---|
| 6 mil plastic | Basic vapor barrier on the floor | Tears easily; fine for a dry space nobody enters |
| 10–12 mil reinforced | Standard encapsulation | Woven reinforcement resists punctures |
| 15–20 mil reinforced | Crawl spaces used for storage or frequent service | Most durable; costs more per square foot |
Thickness is not the whole story. Taped seams, liner fastened to the walls and sealed around piers and pipes matter as much as mil rating.
The Encapsulation Process
- Fix water firstLeaks, grading and drainage problems are repaired; mold is removed from joists.
- Clear and prepOld plastic, debris and failed insulation are removed; sharp rocks are cleared.
- Install the linerA reinforced liner covers the floor and runs up the foundation walls; seams are overlapped and taped.
- Seal openingsFoundation vents and gaps are sealed; the rim joist is air-sealed and insulated.
- Add humidity controlA crawl space dehumidifier or a small conditioned-air supply keeps humidity below 60%.
- MonitorA hygrometer lets you check humidity without crawling in.
Budget numbers for each step are in our encapsulation price breakdown.
Dehumidifier, Supply Air or Exhaust?
A sealed crawl space still needs a way to manage moisture. The IRC allows a few approaches:
Crawl space dehumidifier
Most common for existing homes; drains to a pump or the sump and runs on a humidistat.
Conditioned supply air
A small duct from the home's HVAC keeps the space close to indoor conditions.
Continuous exhaust fan
Pulls a small amount of air out of the crawl space to the outside.
Radon and Encapsulation
Encapsulation is the base for a sub-membrane radon system: a pipe draws soil gas from under the liner and vents it above the roof. Planning both at once is cheaper than adding radon later. Test before and after either way.
Joists with growth are cleaned before the liner goes in; see cleaning mold off crawl space joists.
Benefits
- Stops ground moisture and humid outdoor air from feeding mold on joists.
- Reduces musty odors on the main floor.
- Warmer floors in winter and better HVAC efficiency.
- A clean, usable space for storage and easier service access.
- Creates the base layer for radon mitigation if testing shows it is needed.
Questions to Ask Before You Sign
- Is mold on the joists cleaned first, and is it priced separately?
- What liner thickness goes on the floor and walls, and how is it fastened?
- Which dehumidifier or air supply, and where does it drain?
- How are the vents, rim joist and access door sealed?
- What does the warranty cover, and does it transfer if I sell?
Maintenance After Encapsulation
- Check the hygrometer a few times a year; aim for under 60 percent, ideally around 50.
- Clean or replace the dehumidifier filter on the maker's schedule.
- Make sure the dehumidifier drain or condensate pump is flowing.
- Look for tears after any plumbing, HVAC or pest work, and tape them.
- Keep the access door closed and sealed.
Permits: Adding a dehumidifier circuit or changing ventilation may need a permit. Check with the Eagle Mountain City building department before work starts.
Encapsulation pairs well with our mold removal under Eagle Mountain homes.
Frequently Asked Questions
What is crawl space encapsulation?
Sealing the crawl space floor, walls and vents with a heavy liner and adding humidity control, so ground moisture and outside air cannot keep it damp.
Is crawl space encapsulation worth it?
For crawl spaces with mold, musty odors or high humidity, yes — it addresses the cause. For a dry crawl space with no problems, a basic vapor barrier may be enough.
Do I need a permit to encapsulate my crawl space?
The liner itself usually does not, but electrical work for a dehumidifier or changes to ventilation may. Check with Eagle Mountain City.
Does crawl space encapsulation add value?
It can make a home easier to sell by addressing moisture and mold concerns that show up on inspections.
What thickness vapor barrier do I need for encapsulation?
A 10 to 12 mil reinforced liner is standard; 15 to 20 mil suits crawl spaces used for storage or frequent service.