Crawl space
Crawl Space Encapsulation
Crawl space encapsulation seals the space under your house against ground moisture and humid outside air. Done in the right order it stops the damp that ruins insulation and softens floors. This page explains what the job includes, so you can judge what you are offered.
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What encapsulation is
A vented crawl space is open to two sources of moisture: the soil beneath it and the outdoor air coming through the vents. Encapsulation shuts both out. A heavy plastic liner covers the ground and runs up the walls, the vents are closed, and a dehumidifier keeps the air inside dry. The crawl space stops behaving like the outdoors and starts behaving like part of the house.
- Heavy liner laid over all of the soil, with seams overlapped and taped
- Liner carried up the foundation walls and fastened near the top
- Outside vents closed off and sealed
- Dehumidifier set on blocks, draining to a pump or an outlet
- Liner wrapped up each pier, so no bare soil is left open
- Drain or basin under the liner at the low spot, where water has shown up
- Gaps sealed where the wood framing sits on the wall
The order matters
Water first
If water ever stands under the house, a drain and a pump go in before the liner. A liner laid over a wet floor just hides the puddle.
Clear out
Wet insulation, old plastic, wood scraps and debris are removed so the liner lies flat and nothing rots beneath it.
Line and seal
The liner is laid, overlapped and taped at the seams, fastened to the walls and wrapped around each pier. Vents and gaps to the outside are closed.
Dry the air
A dehumidifier made for crawl spaces is set up with a drain, so nobody has to empty a bucket.
What it disturbs
Nearly all of the work happens below the floor. Expect people going in and out through the access door, bags of old insulation carried across the yard, and some noise under your feet. You stay in the house. If the access door is inside a closet or the hatch is small, say so on the phone, because it changes how the job is planned.
Questions to ask about an encapsulation
- How thick is the liner, and is it reinforced? Thin plastic tears the first time someone crawls over it.
- How high up the wall will it go, and will a strip of bare masonry be left at the top so a termite inspector can still see the wall?
- Is there a furnace or water heater down there that burns gas? Sealing the vents changes where it gets its air, and that needs an answer.
- Where will the dehumidifier drain to, and what does it need in the way of an outlet?
- Is cleaning mold off the joists included, or priced as a separate item?
- What will the wood moisture readings be before the job, and will someone come back to read them again?
- Who do I call if the liner comes loose or the dehumidifier stops?
What usually goes with it
Gutters and downspouts that empty at the wall keep feeding water to the crawl space, so they are often corrected in the same visit: see yard drainage. Joists or a sill that have already softened need repair before they are sealed in. And where the space is dry apart from ground moisture, a plain vapor barrier may be all that is needed. A company that proposes the full system should be able to say why the smaller job would not do.
Living with it afterwards
An encapsulated crawl space is not something to seal and forget. The dehumidifier has a filter to clean and a drain that can clog. Look in once or twice a year: the liner should be flat and dry, the seams closed, and the humidity reading on the unit steady.
Can encapsulation be done in a crawl space that floods?
Only after the water has a way out. That means drainage and a sump pump first, then the liner.
Will it get rid of the smell in the house?
If the smell starts in the crawl space, drying the space is what removes it. Ask the company what else they found, such as a dead animal or a leaking drain line, before assuming damp is the only source.
Do the vents really get closed?
Yes. In humid weather open vents bring in more moisture than they let out. Closing them only works together with the liner and a dehumidifier, which is why the parts are sold as one job.