Provide a moisture barrier over any dirt floors and extending up foundation walls but not up to nor in contact with wood framing or sills.

Moisture barriers may be 6-mil poly or other special basement sealer products such as special moisture-sealing concrete coatings.

The crawl space moisture barrier system shown here uses mechanical fasteners and adhesive to secure the plastic barrier to the foundation walls near the tops (but short of wood framing to reduce insect attack risk).

We install moisture barriers to stop the "pumping action" that draws moisture into a building through the foundation walls or through the crawl space dirt or concrete floor. Moisture pumping occurs as moisture evaporates off of the indoor surface into building air. This process invites movement of additional water molecules through the outside surfaces and into the building.

Choose your crawl space plastic vapor barrier material carefully. Some plastics can give off an obnoxious odor themselves - an effect which may become suddenly noticeable and more significant than you anticipated once you've spread a smelly plastic out over a large crawl space area below a building.

It may take some time for such odors to dissipate. (We don't have data on possible health effects of the volatiles and gases comprising the odor from smelly plastic vapor barriers. Contact us if you do.) The white reinforced plastic material shown in the photos here was not producing any noticeable smells at the time of our inspection.

Our photo shows a successful cleanup of a very moldy crawl area that had a gravel and dirt floor. The framing was cleaned, dried, then sealed with a Fosters™ clear fungicidal encapsulant, and a heavy poly vapor barrier was placed on the crawl area floor and sealed neatly throughout. Even high quality workmanship such as this job may not last however, if the building owners do not take the outside steps to keep water out of the crawl area. .

Moisture warning when installing concrete in a crawl space: Poured concrete or similar dense coating on crawl space floors and lower walls is a crawl space sealing and cleaning process offered by some mold and flood damage remediators as an alternative to the plastic vapor barrier.

Before pouring concrete or similar coatings into a confined space under a building you should determine if the surge of moisture that will be generated under the building is going to be a problem for other building areas.

If so, you'll need to take steps to direct that moisture outside rather than up through the building.

. In hot humid climates, venting a crawl space is actually asking for trouble: moisture-laden warm air entering a crawl space leads to accumulated condensation and water and to a building moisture and often building mold problem.

Be sure that the dirt floor moisture barrier slopes to a drain.

A great many installations we see, even in company product literature, show multiple low spots in a crawl space, each of which is subject to ponding and water retention from leaks or other unanticipated water entry into a crawl space or basement.

How to install a continuous dehumidification system in a crawl space: (with a permanent drain hookup so the system can run unattended. Use an A/C condensate pump to a building drain if a gravity drain connection is not feasible.

First remove the mold, remove any moldy insulation, then correct the water entry problems, then clean the surfaces, then you can put your dehumidifier to work to keep the space dry.

This installation could have done a better job on the plastic but the dehumidifier is well placed near the center of the crawl space.

If your crawl area is large, add one or more small fans blowing towards the dehumidifier from remote areas of the crawl space. You'll find this makes an enormous improvement in the rate of dehumidification.

Don't even bother to try to dehumidify the crawl space if the area is taking on standing water or puddles. First you'll have to solve the water entry problem. Cleaning up puddles or active foundation leaks with a dehumidifier won't work any more than you can suck the dust off a the living room carpet by standing across the house in the kitchen and waving your vacuum cleaner wand in the air. (This is also why an indoor "air cleaner" cannot remove a problem mold or allergen source in a building.)

Don't put a new dehumidifier into a moldy crawl space if you're going to clean up the mold. Doing so will increase the airborne mold level in some cases - yes as things dry out the mold will begin to release more spores than ever. Also you'll contaminate your dehumidifier with mold spores.

We like to set our crawl space dehumidifiers to 45% RH or lower. We've made lots of humidity measurements. When the humidity right close to the dehumidifier is 45%, you'll find that more distant crawl spaces will have a higher humidity level, especially close to the foundation walls. So if you're trying to dry out the whole area, don't set your dehumidifier above 45% RH.