Vapor Barrier Installation in Scotts Valley, CA

Local Context

A Scotts Valley Crawl Space Is Downhill From Everything Above It

Bare soil in a crawl space is a moisture pump. Ground water evaporates upward continuously, and in Scotts Valley the ground under the house has a lot to give: rain concentrated between November and March, hillside lots that collect runoff from uphill neighbors, and canopy shade that keeps the whole sub-area from drying out the way an open valley lot would. Sub-area vents move air, but they cannot dry a space when the outside air is already saturated through the entire wet season.

The damage follows a fixed sequence. Wood moisture content climbs, fungal decay establishes in sill plates, joist ends, and deck ledgers, and softened wood then draws in the organisms that need it — carpenter ants (Camponotus modoc), Pacific dampwood termites (Zootermopsis angusticollis), and the subterranean termites already foraging in the wet soil below. Meanwhile air from that crawl space moves upward into the house, which is where the musty smell in a Scotts Valley living room in February comes from.

A barrier is not a drainage fix, and pretending otherwise wastes your money. If a crawl space off Granite Creek or on the Glenwood side takes standing water in January, the sequence is grading, gutters, and downspout extensions first — and gutters here fill with redwood needles faster than almost anywhere in the county. Once water is being carried away from the foundation, the polyethylene does its actual job, which is stopping vapor from the soil that remains.