How to Dry Out a Crawl Space and Keep it Dry, avoiding crawl space mold, insect damage, rot, & allergens
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Stop water from entering the crawl space from outside: this means attend to roof gutters and downspouts - the most common cause of crawl space water entry or high moisture in most areas.

Our photo shows frozen water in a wet and cold crawl space below a condominium in Poughkeepsie, New York. The very wet masonry blocks along the rear wall of the crawl area and water stains higher on these walls tell us where the water is coming from.

If a building site is unusually wet or springs are adjacent to the building foundation, additional steps such as the installation of a drainage system and sump pump inside or exterior foundation drainage and waterproofing could be necessary.

But before pursuing those costly measures, be absolutely certain that roof runoff and surface runoff have been directed well away from the building.

Inspect the building exterior, from roof to ground, for sources of water that need to be directed away from the structure.

Stop water from entering the crawl space from inside: this means:

• Inspect the building interior, attic to basement and crawl spaces, also looking for sources of leaks, moisture, improper venting, that could affect the structure. In the basement and crawl spaces, look for visual evidence of the pattern of water entry - where has water been entering the building? Trace that water to its source and cause.
• Repair any leaks in building drains over or in the crawl space. Check below bathrooms, kitchens, and also check hot water heating lines or steam condensate return lines in the crawl space.
• Repair any leaks in supply piping in the crawl space.
• Insulate cold water pipes in the crawl space to stop dripping of condensation that forms on the cold water lines in humid weather. It's a good idea to do this in the basement too.

Also see FREEZE-PROOF A BUILDING.

Crawl space venting – this is a debated topic as in humid weather venting outside air into a cool crawl space might increase crawl space moisture.

We no longer recommend simple passive venting nor humidistat-controlled venting except in special circumstances.

When our onsite inspection indicates a long-standing moisture problem in such an area the best current advice is to stop venting the crawl space and to convert it to a dry, conditioned space.

Remove crawl space debris from the area.

Not only are nails, splinters, and possibly rodents that may be in the debris a hazard to workers entering the area, these materials also invite termites, carpenter ants, or rodents which in turn damage the building.

Old cardboard boxes and stored junk invite mold growth and rodents.

Do not bring mold-suspect boxes of stored items out of the crawl space (or basement) back into the living area of the building. Take them outside for inspection and if appropriate, cleaning and salvage.

Is there wet or falling or rodent-infested fiberglass insulation in the crawl area? If so there is a high risk of mold or rodent contaminants that could present a fungal, bacterial, or viral airborne hazard. We recommend completely removing all fiberglass insulation from crawl spaces.

Do not enter such an area without protective gear.

See Mold in Fiberglass Insulation.

Fiberglass is an effective and cost-effective building insulation product that performs very well in many applications. And from the factory you can expect fiberglass building insulation products to be nice and clean. But we do not recommend this material for use in crawl spaces or other tight, limited-access under-building areas nor for use against foundation walls.

If the floors above a crawl area or the rim joist or perimeter of the building need to be insulated we prefer to use spray foam or solid foam insulation in such areas because they resist moisture uptake. Here is a photo of a crawl space that was insulated with spray foam insulation.

But don't insulate the crawl space yet. There is more cleaning, drying, and sealing work needed first.

Remove other Hazardous Materials Such as Asbestos in Poor Condition, or Mold Contaminants from the Crawl Space

Is there asbestos insulation in the crawl space? Often we find a crawl area in which the asbestos pipe insulation is not just hanging (photo at left) but has fallen onto the crawl space floor.

Asbestos pipe or HVAC duct insulation that has been disturbed,damaged, or deteriorated, including asbestos that has fallen to the floor should be removed and cleaned up by a professional.

Do not enter such an area without protective equipment; take care that you do not track hazardous materials out of the crawlspace and into other building areas.

Do not track asbestos debris back into other building areas.

Is there evidence of mold contamination such as areas of wood, paper, or other material covered with mold or mold-suspect material.

If the crawl area has more than 30 sq.ft. of contiguous toxic or allergenic mold it should be cleaned by a professional mold remediation company.

Beware: often the most serious mold we find in crawl spaces is not the mold you see on wood framing but rather the mold you don't see in fiberglass insulation in a damp or wet area. See Mold in Fiberglass Insulation for details.

Beware also of rodent-infested crawl areas; there may be bacterial or viral hazards from these animals, or from their urine and feces, and in some areas there may be a Hantavirus hazard.

Hantavirus pulmonary syndrome (HPS) is a deadly disease from rodents. Humans can contract the disease when they come into contact with infected rodents or their urine and droppings. HPS was first recognized in 1993 and has since been identified throughout the United States. Although rare, HPS is potentially deadly. Rodent control in and around the home remains the primary strategy for preventing hantavirus infection. - US CDC

See Crawl Space Safety Advice and Crawlspace Mold Advice for details. Do not enter such an area without protective gear.

Negative air machines and dust barriers are procedures used by professional mold remediation companies, asbestos removal experts, and building flood damage restoration companies. These measures reduce the risk of blowing contaminated dust and debris into other building areas - an event which could be a health risk, especially to occupants who are in fragile health. Photo courtesy of Anabec, Inc.

Even an amateur, do-it-yourself cleanup project would benefit from these methods.

But you should recognize when your cleanup project needs the help of a professional. Here are some examples of conditions that mean you should hire a professional to clean up a crawl area:

There is asbestos material that needs to be removed

• The area contains a large reservoir of harmful mold, more than 30 square feet of contiguous moldy material
• The area has been contaminated with sewage and sewer backups
• The people who plan to do the cleanup are not fit, healthy, and properly dressed and equipped
• Other building occupants are at particular risk of health effects from stirred-up building dust that may contain mold, fiberglass insulation fragments, bacterial, viral, or other hazards. Examples are the elderly, infants, asthmatics, people suffering from COPD, or people suffering from MCS.

See MOLD EXPERT, WHEN TO HIRE and DO IT YOURSELF MOLD CLEANUP.

If there is room to work, a power washer is a very effective way to clean surfaces, but the increase in water and moisture in the crawl space can make mold or other building-related moisture conditions worse.

In some circumstances such as a crawl area or basement that can be well ventilated, in dry weather, that is well drained, and where other measures are taken to avoid sending a surge of moisture upstairs, power washing might be possible.

Alternative dry-spray surface cleaning methods called media blasting include use of dry-ice spray and baking soda or other abrasive particles, even sand or walnut shell fragments. See Media Blasting for Mold Removal. Our photo shows the ceiling over a basement after cleaning by media blasting.

1. First it is important to physically remove contaminated or moldy materials and debris or materials and debris that have been contaminated with sewage or flood water sludge and mud.
2. Second it is important to physically clean the contaminated surfaces in a crawl space such as moldy joists or subflooring.
3. Third, use of a biocide, disinfectant, or surface encapsulating spray as a final step makes people feel more confident about the mold or sewage cleanup, but although this is a widespread practice, the use of biocides is questioned by experts. One could certainly question the usefulness, effectiveness, and wisdom of spraying carpeting such as shown in our photo. If the carpeting is so infected as to "need" spraying with a disinfectant, it should be removed and the surfaces cleaned instead.
   
   Microban Nuocide™ is an example of a broad spectrum biocidal spray that is in wide popular use by mold and flood damage remediation contractors.
   
   Anabec NG2000™ and Bioshield BST Protectant RTU75™ are also products used in mold remediation projects.
   
   CalBrite™ (Caltex International) is a deck cleaner that was sold to one of our clients as a biocidal spray - it is not.
   

Surface encapsulant sprays are used by mold and flood damage remediators to knock down remaining airborne particles in the work area and to immobilize (the hopefully very few) particles that remain on surfaces and in crevices of a building area after professional cleaning.

We sometimes see encapsulant sprays applied right on top of thick heavy debris or on building insulation. This is an ineffective shortcut that should be avoided. (Photo at above left).

Our laboratory photo shows how a clear encapsulant spray (Fosters 4051™) produced individual "overspray" dried droplets which captured both small particles and some large fiberglass insulation fragments that were airborne at the time the encapsulant was being sprayed in the remediation area.

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.

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.