Basic ground cover compared with sealed encapsulation
Both aim to stop soil moisture. They differ in how far they go.
Ground cover (vapor retarder on the soil)
- Polyethylene sheeting laid over the dirt with seams overlapped.
- Often run a short way up the foundation walls.
- Crawl space usually stays vented to the outdoors.
- Less involved, and often enough for a dry, well-drained lot.
Encapsulation (sealed crawl space)
- Heavier liner sealed at seams, piers and walls.
- Vents closed, with the space dehumidified or conditioned.
- Walls may be insulated instead of the floor above.
- More involved; involves design choices about air and combustion appliances.
Why a dry climate does not mean a dry crawl space
People new to Colorado are sometimes surprised that a crawl space here can smell damp at all. The air is dry most of the year, but the soil a few feet down holds moisture, and irrigation, lawn watering and spring snowmelt keep the top layers wetter than you would think. Exposed dirt under a house gives that moisture an easy way into the cool, still air under the floor.
Many 1950s and 1960s crawl spaces in the west metro were built with no cover at all or with thin plastic that has since torn, been pushed aside by plumbers, or been buried under debris. Each tear lets soil vapor through. A complete, overlapping cover is often the single change that does the most for an earthy crawl space odor.
Ground covers do not fix liquid water. If water runs into the crawl space during storms or pools at a low spot, that drainage problem has to be addressed first, or the cover will simply hold the water on top of it.
Details that separate a good installation from a poor one
| Detail | Done well | Done poorly |
|---|---|---|
| Coverage | Every square foot of soil covered, including around piers | Gaps at corners, piers and the hatch |
| Seams | Overlapped generously and taped or sealed | Edges barely touching or curling up |
| Walls | Run up the foundation and fastened or sealed | Stops at the base of the wall |
| Material | Thickness suited to foot traffic for future service | Thin sheeting that tears on the first visit |
| Prep | Debris, old wet insulation and sharp objects removed first | Plastic laid over trash and puddles |
Before choosing an approach
- Find out whether water ever enters the crawl space as liquid, not just vapor.
- Note where the furnace and water heater are; sealing a crawl space that houses combustion appliances needs careful design.
- Check whether a radon mitigation system or sump is present; the cover must work with it.
- Look at the condition of floor insulation and ductwork that will be affected.
- Ask whether the work needs a permit from your city or Jefferson County.
General information for Lakewood, not a quote or professional advice. In an emergency, call 911.