Wet crawl space unsafe to enter (C) Daniel FriedmanHow to Dry Out the Crawl Space in 3 Steps
Methods to rapidly & thoroughly dry out a wet crawl area after water entry or flooding

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How to fix up a wet crawl space:

Three key steps to get water and moisture out of a building crawl area following water entry, storm flooding, or a sewer backup. Here we summarize a safe and effective approach to removing water from a wet or flooded crawl space. Companion articles add details about debris removal, cleaning, and sanitizing a crawl area followed by advice on how to keep the crawl space dry.

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How to Dry Out a Crawl Space Quickly in Three Steps

Here is a Step by Step Guide to Drying out the Crawl Area and Keeping it Dry

Step 1: Remove crawl space debris and wet materials - without this step the dry-out will be more difficult, take more time, and be more dangerous. Do not try to "dry out" wet or damp or suspect fiberglass crawl space insulation. Just remove and discard it. But don't insulate the crawl space yet. There is more cleaning, drying, and sealing work needed first.

We describe first Clean Out the Crawl Space - that means get rid of insulation, junk, debris, then we describe Clean Up the Crawl Space - that means dealing with mold or other surface contaminants.

Later, when the crawl space has been dried we might also consider using a sanitizer or fungicidal sealant. But not now.

Step 2: Remove standing water in the crawl space. This process can go on more or less simultaneously with debris removal.

At How to Use Sump Pumps in Crawl Spaces we describe that procedure. But depending on the shape of the crawl space floor surface you may need to use one or more portable sump pumps of the type that pick up water from a wet "floor" surface.

If the crawl space floor were flat and drained to one single low point, just one sump pump would usually be enough. But if there are significant puddles or multiple low areas, use one or more portable sump pumps to remove that standing water. Later you'll want to level the crawl space surface so that should water enter it will drain to a single pump location.

Step 3: Remove moisture from the crawl space materials and surfaces. This means dry out wood framing, subfloor overhead, and the crawl space floor surface.

Below at How to Use Heat and/or Dehumidifiers in Crawl Spaces to Keep Moisture Levels Down we describe using a dehumidifier to remove crawl space moisture.

The rate at which a dehumidifier removes water from the air depends on the size of the unit (how many quarts of water it can remove from air per hour) which in turn depends on the cooling capacity of the dehumidifier, ambient temperatures, the moisture in ambient air, and, very important: the rate at which moist air moves from the dehumidified area (crawl space in this case) to and through the unit.

By placing multiple fans around the crawl area you can increase airflow across wet surfaces (crawl space floor, walls, ceiling).

Connect the dehumidifier output directly to a floor drain or direct the output outside of the building to a location at least 10 feet away and where water will continue to drain away from the building. Obviously in freezing weather you'll need to direct dehumidifier output to an indoor drain. Use a condensate pump and plastic tubing if your dehumidifier does not itself include a lift pump drainage system.

Watch out: if you start running air moving equipment in a contaminated crawl space (mold, asbestos etc) before those contaminants have been removed, the air in that space is likely to be unsafe.

Do we need to blow crawl space air to outdoors during the rapid dryout phase?

If the crawl space air temperatures are lower than those in the occupied space above, the thermal updraft that might move moisture (and possibly contaminants) into the occupied space may not be significant.

But if temperatures in the building above and the crawl space are within 10 degF. of one another, or if the crawl space is visibly moldy or suspected of containing other contaminants (rodent debris, asbestos), then you want the crawl space air pressure to be negative with respect to the building above - so we don't push contaminated air upstairs. That means using exhaust fans or if appropriate, professional negative air equipment.


Do we also need to add heat to help dry out the crawl area quickly?

It depends. Warm air carries more moisture than cool air and thus will deliver moisture to the dehumidifier more rapidly. The answer is ... it depends on the relative humidity in the area and ambient temperatures. If the relative humidity (RH) is high, say over 60%, and temperatures are over 60 degF. (this is speculative opinion) you probably won't gain much by adding heat to the crawl space during dryout.

We don't want the crawl area so warm that we start sending moist, possibly moldy crawlspace air riding thermal currents into the occupied space of the building. But if crawl space temperatures are low, say below 50F, you will probably speed up drying by adding some warmth, beyond that already provided by the exhaust side of your dehumidifier fan motor.

This article series describes the steps needed to get into, inspect, clean, and then dry out a building crawl space. We give a step by step crawl space entry, inspection, cleanout, dryout and keep dry guide explains how to get into or inspect a crawl space even if there is no ready access, how to assess crawl space conditions, how to stop water that is entering the crawl area, how to dry out the space, how to clean up and if necessary disinfect or sanitize the crawl space, and how to keep out crawl space water and moisture in the future.


Continue reading at CRAWL SPACE MOISTURE BARRIERS or select a topic from the More Reading links shown below.



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