Drying the Crawl Space That Breeds Flies

What Crawl Space Moisture Correction for Flies Involves and When It Is the Right Call

Fly larvae need wet decaying material. In southern Virginia and northern North Carolina the red clay soil holds water against foundations, summers are humid and many houses sit over crawl spaces rather than basements. That combination keeps crawl space soil damp for months at a time. Add washed in leaf litter, a dripping drain line or a dead rodent, and the space under the house becomes a steady producer of flies.

The inspection is free and it comes first. We look for standing water, wet soil, condensation on ducts and pipes, plumbing leaks and any carcass or debris that is breeding flies. Where a leak or carcass is the whole story, fixing the leak and removing the material may be all the crawl space needs. Where the soil itself is wet and the air is heavy, drying the space is the answer.

Correction follows the wet crawl space sequence. Moisture damaged framing is repaired first. If water collects on the ground, French drain material is laid to a sump pump before anything else goes down. Then a 20 mil poly vapor barrier is laid across the ground and run up the foundation walls and piers, foundation vents are sealed, and a new insulated access door with a gasket replaces the old one. A dehumidifier sized at 70 pints per day per 1,000 square feet holds the air dry after the ground is covered. We obtain building permits and inspections for every encapsulation job.

Expect the flies to fall off as the soil dries and the material they were breeding in is removed, over a week or two rather than overnight. The larger change is that the crawl space stops producing them, and the nuisance pests that lived on the same damp ground drop off with them.

This is the right call when the inspection shows the crawl space is the source. It is not the right call for a drain fly problem at a bathroom sink or a fruit fly problem in the kitchen. We tell you which one you have before any work is quoted.