What a vapor barrier is
A vapor barrier is a sheet of heavy plastic laid over the dirt floor of the crawl space. It blocks water vapor rising from the soil. Sheets overlap and get taped or pinned. The vents stay open. That is it.
What encapsulation is
Encapsulation uses the same kind of liner, but runs it up the foundation walls and seals it there. The vents are closed. Gaps around pipes and wires are foamed. Rigid foam insulates the walls. A dehumidifier controls the air. The crawl space becomes a sealed, dry box.
| Vapor barrier | Encapsulation | |
|---|---|---|
| Covers floor | Yes | Yes |
| Covers walls | No | Yes |
| Vents sealed | No | Yes |
| Dehumidifier | Optional | Yes |
| Stops soil moisture | Yes | Yes |
| Stops humid outside air | No | Yes |
| Charlotte cost | $1,200 to $4,000 | $5,000 to $15,000 |
Pick a vapor barrier if
- The crawl space is mostly dry, with no standing water
- Humidity is under 60% most of the year
- There is no mold and the wood is sound
- The old liner is torn or missing and you just need to replace it
- Budget is the main concern right now
Pick encapsulation if
- There is a musty smell in the house
- You have found mold on the joists
- Pipes or ducts drip in summer
- Humidity sits above 60% under the house
- Insulation is wet or falling
- You want lower energy bills and a long term fix
The common mistake
Many Charlotte homeowners buy a vapor barrier, then find the musty smell is still there a year later. The floor was never the main problem. Open vents let in humid summer air, and that air condensed on the cold ductwork. Only sealing the vents and drying the air fixes that.
Can you start with a vapor barrier and upgrade?
Yes, if the barrier is a thick 12 mil or better liner and is installed well. A contractor can later run it up the walls, seal vents and add a dehumidifier. Tell them your plan so they leave enough material at the edges. Once upgraded, the liner and wall foam last for decades, so the extra cost is spread over a long time.
Questions people ask
What thickness should the liner be?
Does a vapor barrier need a dehumidifier?
Can I just put plastic down myself?
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