What Separates a Real Vapor Barrier From Loose Plastic in Fayetteville

Plastic on the ground is a material, not a barrier

Almost every crawl space in this market has something on the soil. Far fewer have a vapor barrier, and the difference is not the plastic. It is whether the sheet is continuous, held where it was put, and sealed where it stops.

Soil gives up water constantly. A barrier works by putting an unbroken layer between that soil and the air in the space so the water stays in the ground. Leave a foot of bare soil showing at a pier, along a wall or between two sheets that were never joined, and the space carries on humidifying itself through the gap. Moisture does not need a large opening. It needs any opening.

So the honest way to judge a ground cover is to look for the places it stops rather than the places it covers. This page is about the material, the installation and the dehumidifier that sometimes has to follow. Bringing a crawl space fully inside the building envelope is a bigger scope and a separate decision.

Sandy loam under a Fayetteville crawl space drains fast but still wicks vapor upward once summer humidity sets in, which is exactly the condition loose sheeting fails to address. The licensed pros we connect you with find the same gap in older homes out toward Wade and Godwin, where sealed seams and taped piers matter more than the plastic's thickness. Near the Cape Fear River outside Erwin, ground cover without a real perimeter seal barely slows the moisture at all.

Thickness, reinforcement, and where a cheap roll gives up

The film that came with most houses is thin builder grade polyethylene, commonly 6 mil, chosen because it costs little and satisfies an inspection on the day. It does the job that day. It also tears on a nail head, punctures under a knee and splits along a fold, and none of that gets noticed, because nobody looks under a house for years at a time.

A liner meant to last is several times thicker and carries a woven reinforcing layer between its faces, so a tear stops rather than running across the space. That matters more than any figure on a spec sheet, because the way ground cover fails under a house is not slow degradation. It is a hole somebody made and did not see.

Ask what is being installed and get it in writing, then ask what happens when it gets damaged during other work. A liner a plumber will cut through next year should at least be one that can be patched and sealed, rather than one that keeps tearing outward from the cut.

Crawl space humidity plays out differently depending on soil and grading, and that is true whether the job is in Fayetteville or out along I-95 toward Lumberton, where low ground near the Lumber River keeps liners under pressure year-round. The same goes for homes near Wade, close enough to the South River bottomland that a thin roll rarely lasts a full season. The licensed pros we connect you with size the material to the water table, not the invoice.

Seams, wall termination, piers: where quality shows

Three details separate a job that holds from a job that photographs well on the afternoon it was finished.

Sandy loam under a Fayetteville crawl space drains fast, but heavy clay pockets out toward Raeford and Rockfish hold water against the liner long after a storm passes, and that is where a termination strip pulls loose first. The pros we connect you with check pier wraps harder in those stretches, plus anywhere near Toneys Creek or Stewarts Creek where the ground stays damp into summer, since a seam that looked sealed in April can be sagging by August.

• Seams overlapped generously and taped with a tape made for the purpose, not duct tape
• The liner carried up the foundation wall, mechanically fastened, then sealed along its top edge
• Every pier wrapped individually and sealed, rather than the sheet cut around it and left open
• Cuts at plumbing, ducts and posts sealed rather than tucked under
• Material run right into the corners and behind the access opening, not stopped short
• Enough material used that nothing is stretched tight over the ground

The wall and the piers are where most of it is lost

Check the wall termination first. A liner that simply lies flat and stops a few inches shy of the foundation leaves the whole perimeter of the space uncovered, which is precisely where damp soil meets the coolest surfaces in the building.

Pier wrapping is second. A sheet cut in a rough circle around each pier and left open is a common shortcut, and across a house with a dozen piers it adds up to a considerable patch of exposed soil in the middle of a space that is supposedly sealed.

Then the traffic test, which is the real reason fastening is not a detail. A technician has to get into that space to inspect and treat, and so does a plumber, an electrician and whoever runs a duct. Every one of them crawls over the liner.

An unfastened sheet slides under a knee. Two trips across it and the material has bunched into ridges, pulled away from the wall at one end and rolled back off the soil at the other. From the hatch it still looks installed, while a third of the ground underneath is open again. A fastened, taped liner takes the same traffic and stays put, which is most of what the price buys.

That also explains a pattern worth knowing. If a space was covered a few years ago and the readings are climbing again, the first thing to check is not the product. It is whether the product is still where somebody left it.

When a dehumidifier earns its place, and how it gets sized

A dehumidifier is not the first answer and it is not a substitute for the work above it. The order is drainage outside, then a properly installed ground cover, then a reading taken after both. Plenty of spaces come back into range on those two steps and need nothing plugged in at all.

Where a unit does earn its place is a space that still runs humid after the ground is covered and the water outside is controlled. Usually that means moisture arriving through the block wall, through an unavoidably leaky floor above, or as humid outside air moving in through the vents on summer days, which is the case that surprises people most.

Sizing is not the number printed on a box at the hardware store. It comes from the cubic volume of the space, how leaky that space still is once the liner is in, and the moisture load the readings actually show. A unit specified for a dry basement somewhere else will run continuously here and still not hold the space, and a unit that runs continuously fails early.

Then the practical questions, which get skipped more often than the sizing does. Where does the condensate go, and does it get there by gravity or by a pump that will eventually stop. Can the filter be changed without crawling the whole space. Is there a humidistat, and is the target written down somewhere. And is the unit on a circuit nobody will switch off while tidying a breaker panel.

A ground cover installed properly on a typical Cumberland County crawl space runs an estimated $1,100 to $2,600 depending on square footage, pier count and how bad the access is. A dehumidifier is quoted separately and should come with the sizing shown.

Open vents, closed vents, and the tradeoff nobody states

Foundation vents were meant to dry a crawl space by exchanging its air with the outside. That works when the outside air is drier than the air under the house. Through a Sandhills summer it frequently is not, and then the vents are delivering humid air into the coolest space on the property, where it gives up its water on the ducts, the pipes and the underside of the floor.

That is the case for closing them, and it is a real one. Here is the other half, which the people selling the closure tend to leave out. A closed space has no way to dry itself. It now depends on the liner staying intact and on a machine continuing to run, and if either one fails there is no passive route back. A vented space with a wet patch dries slowly. A sealed space with a wet patch stays wet.

There is a middle option in wide use around here: temperature controlled vents that open and close on their own. They are less exact than a sealed space with a dehumidifier in it, and they need no power, no drain and no annual service, which on a rental or a house that changes hands often is a fair trade.

Whichever way you go, write the decision down with the reason attached, because the next person under that house needs to know whether a closed vent is a choice or a fault. And keep the state's figures in view while the work is being planned: beams at least 18 inches above the ground, exterior woodwork a minimum of 6 inches clear of soil, and wood at 20 percent moisture or greater reportable however the vents are set.