Crawl space & moisture
Crawl space encapsulation
A sealed liner on floor and walls, vents closed, a dehumidifier running. Recommended only where it pays off.
Learn more →Vapor barrier installers · Seattle & Puget Sound
Cover the soil. Keep the damp down there.
Bare soil and torn plastic let ground moisture rise into your crawl space all winter. We lay a new ground cover, lapped at every seam and run to the foundation walls, so no dirt is left showing.
- 6-mil minimum, heavier reinforced options
- Seams overlapped, edges run to the walls
- Old torn plastic removed first
Installing and taping a crawl space vapor barrier · Seattle, WAThe problem
The plastic under your house does real work
Soil under a house gives off moisture all the time. In the Puget Sound, where the ground stays wet from fall through spring, that moisture is steady. A ground cover, usually called a vapor barrier, is the sheet of polyethylene laid over the dirt to keep that water vapor from rising into the crawl space and soaking into joists, subfloor and insulation. Washington code requires one in crawl spaces, and for good reason: it's the cheapest moisture control a house can have.
The trouble is that plastic doesn't stay perfect. Plumbers, cable installers and pest crews crawl across it and tear it. Rats chew through it. Thin original sheets get brittle and shift until whole patches of soil are bare. A barrier full of gaps does little. We replace it with a continuous cover: old plastic out, soil smoothed, new sheets lapped generously at every seam, run onto the foundation walls and fitted tightly around piers and pipes.
Warning signs
Signs your vapor barrier needs replacing
One look from the hatch usually tells you. Here's what we look for.
- SIGN 01
Bare soil showing
Any exposed dirt lets moisture rise freely. Patches near the hatch and along the walls are the most common gaps.
- SIGN 02
Torn, shredded or brittle plastic
Plastic that cracks when you touch it, or has tears from foot traffic, is no longer working as a barrier.
- SIGN 03
Sheets that don't overlap
Gaps between sheets, or edges that stop short of the foundation wall, leave bands of open soil.
- SIGN 04
Water pooled on top of the plastic
Standing water on a ground cover means water is getting in from outside. That needs fixing before new plastic goes down.
- SIGN 05
Damp batts or sweating pipes
Wet insulation and condensation on cold pipes point to high humidity in the crawl space, often from uncovered soil.
- SIGN 06
Clear plastic, or none at all
Older homes may have thin clear plastic or nothing. Washington code calls for black polyethylene or an approved equal.
Proof of work
See the difference
Drag the slider to compare. Illustrations of typical results on homes like yours.
BeforeAfterThe job, step by step Tacoma, WA
STEP 01
STEP 02
STEP 03
STEP 04How we do it
How we install a crawl space vapor barrier
A good barrier comes down to coverage and the details at seams, walls and piers.
- 01
Inspection and photos
We go under and photograph the ground cover from end to end, marking torn sections, bare soil, short edges and any water sitting on the plastic. Outside, we check vents, gutters and downspouts for drainage clues. If water is coming in, we tell you before we quote, because a new barrier over a wet crawl space is wasted money.
- 02
Remove old plastic and debris
Old torn plastic, construction scraps, rocks and fallen insulation are bagged and carried out through the hatch. Sharp objects that would puncture a new sheet get picked up, and high spots are knocked down so the plastic lies flat. If rodents have been active, droppings are misted and removed with the rest before anything new goes down.
- 03
Lay the new ground cover
We roll out new sheets across the full crawl space, starting from the far wall. You choose 6-mil black polyethylene, the common code minimum, or a heavier reinforced sheet that stands up better to foot traffic. Sheets overlap generously at every seam and run onto the foundation walls instead of stopping short of them.
- 04
Seal seams, piers and pipes
Seams are taped so the sheets act as one continuous cover. The plastic is cut and fitted around piers, posts and pipes, then taped so no soil shows at the base. Edges along the foundation are held in place so they don't slide back down the wall over time.
- 05
Final check and photos
We walk the crawl space one more time, looking for missed gaps, loose seams and spots where the plastic lifted. You get after photos from the same angles as the inspection photos. Leftover plastic and packaging go out with us, and we note anything that may need attention later, such as vents or downspouts.
What you get
What our vapor barrier installation includes
| Inspection | Free inspection with photos of the full ground cover and drainage clues |
|---|---|
| Old plastic | Torn, brittle or buried plastic removed and hauled away |
| Surface prep | Debris, rocks and sharp objects cleared; soil smoothed |
| Material | 6-mil black polyethylene or heavier reinforced sheeting |
| Seams | Generous overlaps at every joint, taped |
| Edges | Run onto the foundation walls, never stopped short |
| Piers and pipes | Plastic cut, fitted and taped around each penetration |
| After photos | Before-and-after photos taken from the same angles |
Diagram
- 1Vapor barrier
- 2Taped seams
- 3Pier wrap
- 4Floor insulation
- 5Foundation vent
Compare
Standard 6-mil or a reinforced sheet
Both meet the code minimum. The difference is how well they hold up to the people and pests that use your crawl space.
| Factor | 6-mil polyethylene | Heavier reinforced sheet |
|---|---|---|
| Code | Meets the common code minimum | Goes beyond it |
| Durability | Fine for crawl spaces rarely entered | Holds up to foot traffic and repair crews |
| Puncture resistance | Can tear on rocks and debris | Reinforcement resists tears |
| Typical use | Standard vented crawl spaces | Frequent access, storage or encapsulation |
| Cost | Lower | Higher |
Puget Sound homes
Ground cover for a wet-winter climate
Around Puget Sound, the soil under a house rarely dries out between October and May. In a vented crawl space, the ground cover is what stands between months of wet soil and your floor framing. That's why we pay so much attention to it. On the Eastside, many homes built from the 1970s through the 1990s still have their original plastic, now torn and shifted. In older Seattle houses, we often find no ground cover at all, or a few sheets of clear plastic from a past repair with bare soil around them.
A good ground cover also works with the rest of the house. Gutters choked with moss and downspouts that dump next to the foundation can push water under the plastic, where it pools on top. We look for that during the inspection. For most Seattle-area homes, a quality vapor barrier with open, screened vents is enough. Where the crawl space stays damp even with good plastic down, we'll talk through whether encapsulation makes sense and show you the moisture readings behind the advice.
Pricing
What shapes the price
Vapor barrier jobs are priced by the space and what's in it. These are the main factors.
- FACTOR 01
Crawl space size
Square footage sets how much sheeting goes down and how long the crew spends under the house.
- FACTOR 02
Old plastic and debris
Removing torn plastic, debris and droppings first adds time, depending on how much is there.
- FACTOR 03
Sheet weight
Standard polyethylene costs less than heavier reinforced sheeting. We'll show you both.
- FACTOR 04
Piers and penetrations
Every pier, post and pipe means cutting, fitting and taping. Crowded crawl spaces take longer.
- FACTOR 05
Access and clearance
Low clearance and tight hatches slow the work, especially when moving heavier sheeting into place.
The company was quick to respond and send out Ron. Ron was great in communicating the issues we were having in our crawlspace. Had showed us the pictures of the crawl space and was able to get us booked the very next day. The crew was fantastic and worked throughout the day. The bonus was they were also able to take a handful of containers to the dump to assist saving us a dump run.
FAQ
Crawl space vapor barrier installation: questions we hear
Still unsure? Call (800) 674-4933 and talk it through with us.
What thickness vapor barrier does a crawl space need?
Washington code calls for a ground cover of at least 6-mil black polyethylene or an approved equal, laid over all exposed soil. That works well in a crawl space nobody enters often. If plumbers, pest crews or you go under the house regularly, or you want to store things there, a heavier reinforced sheet holds up much better to knees and tools.
Should a crawl space vapor barrier go up the walls?
It should run onto the foundation walls rather than stopping short, so the soil at the edges stays covered. In a vented crawl space, the cover doesn't need to go all the way up and be sealed at the top of the wall. That full wall treatment, with sealed vents and a dehumidifier, is encapsulation, which is a different job.
How much should vapor barrier sheets overlap?
Enough that soil never shows at a seam, even after people crawl across it. Code sets a minimum lap at the joints. We lap generously and tape the seams so the sheets can't pull apart. Short laps are the most common reason a ground cover starts showing bare dirt within a few years of going in.
Can a vapor barrier go over wet soil or standing water?
Over damp soil, yes, since that's what it's for. Over standing water, no. If water collects in the crawl space, it's coming from somewhere: usually roof water from gutters and downspouts, soil that slopes toward the house, or a plumbing leak. We find the likely source during the inspection, and the water needs to be handled before a new barrier goes down.
Do I need to replace my vapor barrier if it has a few tears?
Not always. A few small tears in otherwise sound plastic can be patched and taped. If the sheets are brittle, shifted, short of the walls or torn in many places, replacing the whole cover is usually a better use of money than chasing patches. We photograph the full crawl space and show you which situation you're in.
How long does a crawl space vapor barrier last?
It depends more on traffic, pests and the sheet itself than on age alone. Plastic that nobody walks on and rodents can't reach lasts a long time. Covers in crawl spaces with frequent repair visits or rat activity wear out much faster. Sealing rodent entry points and choosing heavier sheeting where people crawl are the two best ways to make a new barrier last.
Related services
Often done together
Crawl space & moisture
Moisture barrier installation
A full moisture plan for your crawl space: barriers, vents, gutters, downspouts and drainage clues.
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Crawl space & moisture
Crawl space cleaning
Droppings, fallen insulation, torn plastic and debris bagged and hauled out from under your house.
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Crawl space & moisture
Crawl space insulation installation
New underfloor batts, fitted tight to the subfloor and supported so they stay up.
Learn more →Let's see what's going on up there.
Book a free inspection. We'll photograph your attic and crawl space and walk you through what we find, before you decide anything.