These two get used as though they mean the same thing, and they do not. One is a
component. The other is a system that usually includes it.
A vapor barrier covers the ground
A vapor barrier is sheeting laid over the dirt floor of a crawl space to stop moisture
rising out of the soil into the space above. That is a real and useful job. Ground moisture
is a steady source of humidity under a house, and covering it removes that source.
What a vapor barrier does not do is address the other way moisture gets in. In a vented
crawl space, warm humid outside air comes through the vents and condenses on every cool
surface down there. A vapor barrier on the ground does nothing about that.
Encapsulation seals the whole space
Encapsulation seals the crawl space off from outside air and ground moisture, and
insulates it, so the space stays dry and stable instead of following the weather. Sealing
and insulating are both part of it, and one without the other does not do the job.
The reason this matters in East Tennessee is our summers. Vented crawl spaces were built
on the idea that outside air would dry the space out. In a humid climate the outside air is
warmer and wetter than the crawl space, so what actually happens is that moisture condenses
underneath your house. Sealing the space stops that cycle rather than ventilating into it.
| Vapor barrier | Encapsulation | |
|---|---|---|
| Covers ground moisture | Yes | Yes |
| Stops humid outside air | No | Yes |
| Includes insulation | No | Yes |
| Affects energy use | Little | Generally helps |
| Relative cost | Lower | Higher |
Drainage comes first either way
Neither one is the right first step if there is standing water under your house. Sealing
over an active water problem traps it rather than fixing it. Where a crawl space is taking
on water, drainage goes in first. A crawl space drain is a four inch corrugated perforated
pipe with a sock cover, installed along the interior footer to carry water to a sump pump or
to a low spot where it can leave by gravity, and back filled with gravel.
Once the water is handled, then the question of barrier or full encapsulation is worth
asking. We will tell you which one your crawl space actually needs, and the inspection is
free.
Common Questions
Is a vapor barrier enough on its own?
Sometimes, in a crawl space that is already dry and well drained, where ground moisture is the only source. In most East Tennessee crawl spaces it is not enough by itself, because humid summer air coming through the vents is a bigger source than the ground is.
Do I have to close the vents to encapsulate?
Yes. Sealing the space is the point. Leaving vents open while sealing everything else means you are still inviting in the humid air that caused the problem.
Will encapsulation make my floors warmer?
Many people notice that it does, because the space directly beneath the floor is no longer damp and unconditioned. How much difference you feel depends on your house and how the floor is insulated.
Can I still store things in an encapsulated crawl space?
In most cases yes, and it is usually a better storage space afterward because it is dry. We will let you know if anything about your particular setup makes that a bad idea.
Call us at (865) 675-4177 and we will talk through what you are seeing. The inspection and the estimate are both free.