All homes with crawlspaces should have a vapor barrier because the ground contains moisture and that water naturally evaporates from the soil.
A vapor barrier prevents the moisture in the ground from escaping where the vapor barrier is installed. But sometimes, a vapor barrier isn’t enough. Runoff (surface) water can penetrate foundation walls and ground water can seep up through the soil into your crawlspace. Then a French drain is needed to divert the water to a drain system which directs the water from under the crawlspace and away from the house. Sump pumps are sometimes needed when there is not enough “fall” on the outside of the house for a gravity drain to work properly.
Vapor barriers are simply sheets of polyethylene placed in the crawlspace in a way that prevents moisture from escaping into the air. A minimum of 6 mil is recommended to reduce the opportunity of ripping or punctures. In all cases, the edges of each sheet overlaps the other sheets to complete a solid barrier. In crawlspaces where moisture is not really an issue, a simple vapor barrier with overlapping edges covering all areas up to the foundation walls can be sufficient. In other cases where ground water is present or surface water is suspected of penetrating the foundation walls, a super vapor barrier may be needed. The super vapor barrier overlaps the other sheets of poly and the edges are tapped. The poly is extended up the foundation wall until it is at least 6 inches above the exterior grade. This configuration forces the moisture below the barrier and into the drainage system.
Our French drains include corrugated pipe surrounded by 57 granite stone and wrapped in filter fabric. These pipes channel the water to either a catch basin with a sump pump installed or to a discharge line dug under the footer and piped away from the house where gravity lets it drain naturally.
All water in a crawlspace is captured by French drains and diverted either outside via a gravity drain or to a catch basin. Sump pumps are used to pump the water from the catch basin to an area far enough away outside so the water can’t re-enter the crawlspace.