Controlling Crawl Space Moisture in the Right Order

What Controlling Crawl Space Moisture Involves and When It Is the Right Call

Why does the framing come first? Because everything after it covers the framing up or depends on it. Joists, sill plates, band boards and girders that moisture has weakened are sistered or replaced before any drain or barrier goes in, so the work that follows protects sound wood and nobody has to cut open a new barrier to reach a rotten joist. Many of these projects include framing repair.

Why does drainage come before the barrier? A vapor barrier stops vapor. It does nothing useful against liquid water, and laid over wet ground it traps water underneath, keeps the soil saturated and pools where the poly dips. Where water enters as liquid, French drain material along the footing carries it to a sump pump first. Then the ground is dry enough that a barrier over it is stopping vapor rather than hiding a puddle. Where the inspection finds no liquid water, this step is skipped, and that is a decision made under the house rather than from the driveway.

Why does the barrier come before the dehumidifier? A dehumidifier removes moisture from air. Bare soil gives off vapor continuously, and open vents bring in humid outside air all summer. A dehumidifier over bare ground with the vents open is trying to dry the outdoors, and it runs constantly without catching up. With R 10 insulation board on the walls, 20 mil poly sealed across the ground and up the walls and piers, the vents sealed and a gasketed door in place, the remaining moisture load is small and steady, and a dehumidifier sized at 70 pints per day per 1,000 square feet can hold it.

What should you expect? A sequence rather than a single visit, and honest advice about which steps your crawl space needs. Expect us to look at gutters, downspouts and grade outside and to tell you when part of the problem is outside the house. The system needs the door kept closed and the dehumidifier and sump checked from time to time.