Flooded Crawl Space: What You Need to Know and Do

Crawl Space in Unfinished House
Photo Credit: RBerteig

If you live in a flood zone and the crawl space under your house isn’t correctly designed, there’s a good chance you’ll have to deal with a flooded crawl space at some point. Flooding in this area shouldn’t be ignored. It can lead to mold growth that rots your floors and the wood framing of your house, causing serious structural damage. Mold can also make its way into your living space, where it will worsen your indoor air quality.

By cleaning up your flood-prone crawl space and making a few design upgrades, you can protect your home and your health, and even regain your crawl space as a storage area.

Efficient Flooded Crawl Space Clean Up

The job of cleaning a flooded crawl space starts with removing the standing water. If all you have are a few puddles, use a wet-vac to suck up the water and dump it outdoors.

For widespread flooding that doesn’t reach more than an inch deep, you can try sweeping the water out with a push broom. Using a general purpose pump, however, will get the job done more efficiently and it’s the only practical option if the space is severely flooded.

To remove water from your crawl space with a pump, place the pump’s suction hose into the flood water and direct the drainage hose outdoors away from the house. The drainage hose should release the water far enough away from the house that it can’t flow back into the crawl space. Switch the pump on and let it run. You may have to re-position the suction hose periodically until all standing water is removed.

While the pump is running, remove all wet materials from the crawl space. This includes any stored items, soaked insulation, and debris the flood water carried in or knocked loose from the crawl space’s interior. Wet items hold in water and lengthen the time it takes to dry the space. Water-damaged insulation is no longer efficient, so throw it out and replace it rather than trying to dry it.

How to Dry Out a Flooded Crawl Space

When all the standing water is out, you can begin drying the space more thoroughly. This means drying the wood framing, the subflooring above the crawl space, and the crawl space floor.

Before you start, make sure all mold and moldy materials have been removed, that there are no lingering puddles, and that no water is still entering the crawl space.

Once this is done, clean the surfaces inside the crawl space to discourage the spread of mold, which can contaminate your air and your dehumidifier. Check for wiring damage or other issues that would make it unsafe to use the outlets in or near the crawl space. These should be repaired before you bring in electrical equipment to help with drying.

Next, bring in a portable dehumidifier. A large room dehumidifier is enough for a small crawl space, but for a larger one, you may need to rent a commercial grade model. Set the dehumidifier for between 30 to 45 percent and let it run for several hours, then check on the space. A wet crawl space could take a total of eight to 10 hours to dry.

Warm, moving air picks up moisture more readily. To speed up the drying process, place a source of low heat, such as a light bulb, inside the crawl space and position one or more electric fans where they’ll blow air across damp surfaces.

If you plan to use your crawl space for storage and want to ensure it stays dry permanently, you’ll most likely need to install a permanent dehumidifier along with a heat source. Before you do, consult with a professional who can help you ensure the job is done safely.

Effective Crawl Space Flooding Solutions

If your crawl space has already flooded, then you know that layer of plastic on the floor isn’t going to do much against moisture when a severe storm hits. Crawl space flooding isn’t inevitable, though, and it’s not even particularly difficult to prevent.

Before you consider upgrading your crawl space, address the drainage around your home. Ineffective exterior drainage leads rain runoff toward your home and into your crawl space, instead of draining that water away as it should. Check your gutters and down spouts, as well as the grade of the land surrounding your home.

A sump pump should be you next consideration. Not all crawl spaces need one, but in flood-prone areas, these devices provide effective backup when you’re not able to completely stop water from entering.

If you choose to install a sump pump, dig a drainage channel around the edges of the crawl space. This will lead water on the floor toward the sump pump. The floor should be flat enough to prevent puddles from forming. If the floor isn’t flat, level it out.

A sump pump alone can’t keep a crawl space completely dry. If that’s your goal, you’ll need to encapsulate (seal) the crawl space. That requires covering the floor with a vapor barrier, installing vent covers, and adding an airtight door. This approach isn’t appropriate for all climates, so before you start work, consult a professional so you don’t inadvertently worsen your home’s moisture problems.

Using Flood Vents for Crawl Spaces

Flood vents are another way to protect your crawl space and the rest of your house from water damage. A flood vent is a permanent opening in the wall between your crawl space and the outdoors. It’s designed to let water pass through the space freely so that it doesn’t become trapped and create pressure that can damage your walls and foundation.

If your home is built on a flood plain, these vents may be required or recommended by local or national building codes, government agencies or your insurance company. The Federal Emergency Management Administration (FEMA) recommends homes on flood planes have at least two flood vents, each positioned on a different wall. These vents should provide at least 1 inch of open space for every square foot of enclosed crawl space.

The positioning and size of flood vents you’ll need depends on your home’s floor plan and overall design. The standard-size crawl space flood vent is 16 1/4 inch by 8 1/4 inch, the same size as a standard cinder block. Two vents of this size are usually enough to vent a space of 250 square feet or less.

Crawl space flooding is a common problem, but it isn’t something you have to or should put up with. Standing water and lingering dampness should be removed to prevent damage to your home. Once you get your flooded crawl space dry and clean again, consider approaches for preventing future flooding or at least minimizing flood damage. That might mean installing flood vents, encapsulating the space or investing in another type of upgrade.

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