Crawlspace Basics – Help to Dry A Crawlspace

Nothing like the smell of a wet crawlspace.  Which part do you like best?  The possible mold? The dead animals?  Better yet, excrement from those animals?  A little bit of sewage?  You get to get in there and dry it.  But hey, at least you are going to get to lay down on the job right?  Oh, we forgot to mention the snakes, and the spiders, and any animals that are still calling it home.

It is probably not your favorite part of the job.  Most likely it is too short to get equipment under there.  There is probably no power in there to run drying equipment.  In most cases there are no lights.  Insurance companies don’t like to pay to dry dirt.  Oh, and we have to keep all that good stuff that you are blowing around away from the main part of the house so we have to keep that under negative pressure.

Crawlspaces present unique challenges, in both logistics and drying.  For these reasons many technicians avoid crawlspaces or dread dealing with them.  And we haven’t even talked about how to dry them yet.  Before we decide how to dry them we need to understand the basics well.  If you do this then you will be able to dry the crawlspace like an expert.

Crawlspace Exterior Components


Should they be open or closed?  It depends on the drying strategy.  The vents do allow you the ability to draw air into the crawl in a balanced fashion.  If this is part of the drying strategy, which we will discuss later, open them.  If not, like when you are using dehumidification to remove moisture, close them.


The type of entrance available is highly variable depending on what region of the country you live in.  If there is a door to the outside in addition to it being how you get in and out of the crawlspace, it will likely be used as an exit point for air.  Often you will be ventilating out of the crawlspace through this opening.

In the case that there is no access or extremely limited access to the crawlspace from the outside, you will have to open an entry point on the inside of the building.  This will likely mean cutting an opening through the floor in a closet or another room.  This opening should be protected against fall hazard and you also want to make sure that air is not being drawn up through this new opening into the building.  Stack effect, or the natural rise of air through a building, will cause air to move up from the crawlspace into the building unless you use negative pressure in the crawl to pull it back down.

Crawlspace Interior Components


Soil is highly porous.  It will accept and release water very quickly.  The concern here is that too much Evaporation Potential and air flow will create a rate of evaporation that is greater than your ability to remove humidity from the crawl.  That forces moisture into the structural materials or at best brings drying to a halt.

Moisture Barrier

A poly sheeting, depending on region, is often installed over soil.  This is done to trap moisture in the soil and keep it out of the house.  Usually these are improperly installed or in disrepair and therefore release a lot of moisture from the soil.  If this is the case it may need to be repaired or replaced to facilitate drying.

Structural Materials and Concrete 

These materials have bound water or water that is more difficult to remove.  They require higher Evaporation Potential and air flow to remove moisture.  This can be a challenge to create especially when you can’t even get yourself or equipment into the crawlspace.


Usually there is no power source in the crawl or if there is power it is not sufficient.  We need to bring power to this area safely and quickly.  A power distribution box may be used for larger losses.  Properly sized extension cords can be used to provide power for smaller losses.

This information was taken from Episode 3.2.1 of the Reets.TV Water Restoration Pro Package.   For more information drying crawlspaces or full access to this Online Training please visit www.reets.tv


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