Crawl Space Encapsulation Problems: What Goes Wrong and Why

Problem 1: The water was never solved first

This is the failure we are called to correct more than all the others combined. A crawl space that takes groundwater or surface water gets a liner installed over the soil, and the system works for one dry season. Then the water returns, arrives under the barrier, and has nowhere to go, because the barrier is doing exactly what it was designed to do. Seams lift where water pools, the underside of the liner stays permanently wet, and the odor gets worse than it was before the work.

The correct sequence is drainage first, liner second. Interior perimeter drainage bedded in washed stone, tied to a sealed sump with a check valve, installed under the barrier so water is collected and pumped out rather than sealed in. In Metro Atlanta this matters most on the Chattahoochee corridor lots through Roswell and Peachtree Corners, the Nancy Creek bottom in Brookhaven, and anywhere shallow bedrock perches water, notably Stone Mountain and Smoke Rise.

Problem 2: No dehumidifier was installed

A sealed crawl space with no dehumidifier is not a finished system. Georgia's residential code permits an unvented crawl space specifically when a Class 1 vapor retarder covers the ground and an appropriately sized dehumidifier is provided. Those two elements go together. The Department of Energy's assembly guidance for unvented, insulated crawlspaces says the same: continuous ground cover, insulated perimeter walls, and a conditioned space. Sealing the vents removes the ventilation pathway, and without mechanical dehumidification the residual moisture from the foundation walls, from air leakage and from occasional plumbing events has no way out.

This failure is common because the dehumidifier and its dedicated circuit are $2,000 to $3,600 of the quote, which is exactly the line item a homeowner comparing three bids is most tempted to remove, and exactly the line item a low bid removes for them.

Problem 3: The liner stops short of the wall

A liner that covers the floor and stops at the base of the foundation wall is a vapor barrier, not an encapsulation. The block or brick wall is itself a moisture source, wicking ground moisture up through the masonry, and in a sealed crawl space that moisture has nowhere to go but into the air. A proper encapsulation runs the liner up the wall and mechanically fastens it with a termination bar or fasteners and sealant.

The wall termination is also the most labor-intensive part of the job, which is why it disappears from underpriced installations. When you compare quotes, ask specifically whether the liner runs up the walls and how it is fastened. A dramatically low bid on a low-clearance crawl space has usually priced the floor area and planned to skip this.

Problem 4: Mold was sealed in rather than removed

Installing a liner over a crawl space with active growth on the framing does not stop the growth. It changes the humidity, which slows it, but wood at 20 percent moisture content with established colonies does not become clean because a sheet of plastic was laid on the ground beneath it. The correct order is remediate, dry the framing to a verified wood moisture content below 16 percent, then encapsulate.

Problem 5: The termite inspection band was covered

Georgia's structural pest control standards depend on an inspector being able to visually read the foundation masonry for termite tubes. A liner run all the way to the sill covers that band. Some pest control providers will treat that as a condition that limits or voids the terms of a bond, and the homeowner discovers it at the next annual inspection rather than at the time of the work.

The fix is straightforward and has to be planned rather than discovered: hold an inspection gap of several inches at the top of the wall termination. Tell your pest provider before the work is scheduled, because the specific requirement varies by company and it is a five-minute phone call.

Problem 6: Combustion appliances were not accounted for

If a gas water heater or furnace with atmospheric venting is located in the crawl space, sealing that space changes the air available for combustion and can affect draft. This is uncommon in Metro Atlanta, where most crawl space equipment is a furnace with sealed or power venting, but it does occur and it is a safety question rather than a performance one. Any contractor who encounters an atmospherically vented appliance in a crawl space and does not raise it before sealing has skipped a step that matters.

Problem 7: The system was never verified

The most quietly common problem is that nobody checked. The crew finishes, the liner looks excellent in the photographs, and no one returns to confirm that the crawl space actually holds below 60 percent relative humidity in August. A dehumidifier that is undersized for the load, or set to a target it cannot reach, will run continuously and never get there, and the homeowner finds out a year later when the smell returns.

Comparing what you are actually buying

Is encapsulation still worth it?

In Metro Atlanta's climate, yes, for most homes with a crawl space. Roughly 50 inches of annual rain and summer dew points above 65 degrees make a vented crawl space a moisture importer for four months of the year. The failures listed above are all failures of sequencing, specification or verification, and every one of them is visible in the quote before you sign it. The question worth asking is not whether to encapsulate but whether the quote in front of you describes a complete system.