Crawl space vapor barriers in Tupelo
Covering the dirt is usually the least expensive way to cut down on the moisture rising into a Lee County crawl space.
Exposed soil under a house gives off water vapor all the time, and the clay ground around Tupelo can stay wet long after a rain. A ground vapor barrier, usually polyethylene sheeting, sits between that soil and the crawl space air and keeps much of the moisture where it belongs.
Why does the old plastic fail?
Some older Tupelo houses never had any ground cover. Others got a thin sheet at construction that has since been ripped up by years of plumbers, HVAC techs, cable installers and pest control crews crawling across it. Plastic that's shredded, bunched against a wall or buried under dirt isn't stopping much moisture.
How does the code treat a ground cover?
Section R408 of the International Residential Code normally calls for 1 square foot of vent opening for every 150 square feet of crawl space floor in a vented crawl space. If the ground is covered with a Class I vapor retarder, that requirement drops to 1 square foot for every 1,500 square feet. In other words, the code counts a good ground cover as doing a lot of the work vents would otherwise do. The code also says the under-floor area should be cleared of vegetation and organic material.
Signs of a good installation
- Old plastic, roots, sharp rocks and wood scraps removed first
- Seams overlapped generously and taped
- Edges run up the foundation walls and around each pier
- Material tough enough to survive the next service visit
- Any standing water fixed before the new sheet goes down
Ground cover or full encapsulation?
A ground cover handles moisture rising from the soil, but the vents stay open to sticky summer air. If ducts still sweat or the musty smell sticks around after new plastic is down, sealing the crawl space may be the next step. Read about encapsulation.
Signs your vapor barrier is done
- Bare clay showing through rips or gaps
- Water sitting on top of the plastic
- Sheeting that was never attached to the walls or has pulled loose
- A damp smell even though "there's plastic down there"
Every price comes from the crawl space company, after someone has actually been under your house. We don't quote prices, and any number you hear over the phone before an inspection is a rough guess at best.
Where we connect you with help
Common questions
What thickness should a crawl space vapor barrier be?
The IRC asks for a Class I vapor retarder, and 6-mil polyethylene is a common minimum. Many companies install thicker, reinforced liners that stand up better to foot traffic.
Will new plastic get rid of a musty smell?
It often helps when most of the moisture comes from the ground. If humid air through the vents is the main source, sealing the crawl space may also be needed.
Related services
More background: Tupelo crawl space guide.
Musty air, a bouncy floor or water under the house?
Call and we'll connect you with a crawl space company that works in Lee County.