Crawl space vapor barrier in Pasadena CA - ground covered and sealed up the walls

The two choices that move the cost most are how much of the crawl space you seal, a floor liner or full encapsulation, and how thick a liner you pick. After that it comes down to the size of the space, how tight the access is and how much has to be cleared out first. I'll give you the number for your house in a written estimate after I've been down there.

A vapor barrier covers only the crawl space floor to cut down ground moisture, while encapsulation also lines the walls, seals the vents and adds a dehumidifier, sometimes with insulation and drainage. Closing the vents isn't a small add-on, because an older federal guide warns that sealing vents alone can raise moisture and can be deadly if a furnace or water heater down there depends on that outside air. If you have gas equipment in the crawl space, I'll check it before we talk about closing anything.

One crawl space guide puts a 12-mil reinforced liner at 15 to 20 years and a 20-mil liner at 20 to 25 years or more, mil being the sheet's thickness in thousandths of an inch. Under the house the plastic is out of the sun and weather, so what usually ends it early is a tear from someone crawling over it, seam tape drying out or a pipe opening that was never sealed. A thicker sheet costs more now and pushes back the day you replace it.

Clear out anything you've stored down there and any loose debris you can reach, so the liner can cover the ground all the way to the walls. Make sure we can get to the access door easily on the day, and we'll handle the rest of the clearing.

Only on a small job, because California's exemption for minor work tops out at $1,000 and applies only to work that needs no permit, done by someone with no employees on the job. Anything bigger, or any job with a crew, calls for a licensed contractor. We're licensed and fully insured, and our own trained crew does the work.

Federal installer guidance calls for a liner at least 6 mil thick that covers the whole floor, or as close to it as you can get, and runs up the walls, columns and footings, which makes it a fair yardstick when you compare quotes. In a crawl space that's kept closed, the same guidance has the seams and pipe openings sealed with a sealant made for the liner, and any rips from other work down there sealed before the job counts as done. Water comes first, though, since research from Louisiana found a ground cover can do more harm than good if rainwater ends up on top of it.