A high-quality moisture barrier should never need replacing, because good material won't delaminate or break down over time. You may need a new one if yours is flaking or doesn't cover all the ground, is soiled by animal waste, has water sitting on top of it, or is heavily dirty, ripped or torn. Light dirt alone usually isn't worth replacing it over.
At a glance
| What you see | Replace it? |
|---|---|
| Flaking, decaying, or bare dirt showing | Yes, before it degrades further |
| Animal or pest waste | Often. Seal out pests first, then decide based on how soiled it is. |
| Water pooling on top | Fix the water first. Replace if it's heavily soiled or stays wet. |
| Light dirt and debris, good coverage | Usually not. Clean it instead. |
| Heavy dirt, major rips, tears or delamination | Yes |
Delaminating or poor coverage
If your barrier is decaying or flaking, it may need to be replaced before it gets worse. And if any dirt is visible in your crawl space, an inspector would say the barrier has insufficient ground coverage, meaning some of the ground isn't fully covered by plastic.
That matters most in summer, when warmer temperatures make the water in the soil evaporate. That water vapor gets absorbed by any porous material nearby:
- Fiberglass insulation, which can then sag and fall
- The wood framing, pushing its moisture content above safe levels
- Anything you have stored under the house
It also raises crawl space humidity, which can lead to mold on the wood or on the paper backing of insulation. A barrier with full coverage that's correctly overlapped and staked down slows this down.
In summer (or year-round if you have a high water table) you can pull back the edge of the barrier and see water droplets on the underside. That's water evaporating from the soil and condensing under the plastic. If you see condensation on the foundation walls, piers, wood or other surfaces, you'll need more than a moisture barrier. See Why is my crawl space wet without plumbing leaks?
A note on French drains: If your crawl space has an interior French drain, it may be left uncovered, at least on the sides of the home where water comes in. That's okay. Water entering the crawl space has to be able to reach the drain. If the barrier covers the drain, water can run across the top of the plastic and pool somewhere else.
Animals and pests
If animals or pests can get into your crawl space, they're likely leaving urine and droppings on your barrier (and in your insulation). First, find and seal every way in:
- Openings near your HVAC unit that may need metal flashing
- Gaps around pipes and wires that pass through the foundation wall
- Crawl space doors with gaps or holes the width of your pinky or larger
Once there are no more ways in, or a crawl space contractor has done a rodent exclusion, you can decide whether to replace the barrier based on how heavily it's soiled. Bacteria and contaminants from animal waste can be carried into your living space by the home's natural airflow, the stack effect. It's the same reason mold in the crawl space is a concern for the home above.
Water intrusion
If water is getting into your crawl space, fix the source before you do anything with the barrier. If your barrier already has good coverage, the water is probably coming in over the top of it and puddling in low spots. In warm months it evaporates and gets absorbed into the wood and insulation above, causing moisture damage. For help tracking it down, see What should I do about water in my crawl space?
Once the water is handled, you may want to clean or replace the barrier if it's heavily covered in silt or debris. A barrier that stays covered in water will keep adding to the moisture problem and needs to be replaced.
Dirt and debris
If your barrier has good coverage and only a little dirt and debris, there's not much benefit to replacing it. If you have an adequate barrier but still have high humidity, high wood moisture readings or mold, something else is going on. See Why is my crawl space wet without plumbing leaks?
For a barrier with some dirt and debris but no major animal problem, you may not need to change anything:
- Have any trash or debris cleaned out.
- Blow loose dirt toward the door with an electric leaf blower, then pick up what's left with a shop vac.
- Expect some staining to remain even after cleaning.
Never use a gas-powered tool under your home without proper ventilation.
For a barrier with heavy dirt and debris, animal waste, or major rips, tears or delamination, we recommend removing the old barrier and installing a new one. New barriers should be staked down so they don't shift and the ground stays fully covered. See our vapor barrier installation service or book a free inspection.