What is The Ideal Crawl Space Humidity Level – and How Do I Maintain It?

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Do you have a home with a crawl space? 

This article introduces several basic things you need to know about maintaining a proper humidity level underneath your home.

Maintaining an appropriate crawl space humidity level is essential for discouraging mold growth and other unhealthy conditions.

Common Crawl Space Moisture Issues

what should the humidity in my crawl space be

Abnormally high moisture in a crawl space contributes or causea the five most frequent problems found in a house with a crawlspace:

  • pests
  • mold
  • buckling floors
  • cold floors, and
  • wood rot

It used to be assumed that installing crawl space vents would fix moisture issues by letting the humidity escape.

In fact, adding vents can make your crawl space moisture problems even worse.

According to an Advanced Energy study, implementing extra ventilation to boost crawl space airflow actually causes higher relative humidity levels and increases energy loss.

Additionally, it exposes your house to pests and invites them in – door wide open.

The Advanced Energy field research shows that insulated crawl spaces exceed ventilated spaces in terms of resisting pests and rodents.

Here are the most significant findings in this study regarding ventilation’s impact on crawl space moisture:

  1. In sealed crawl spaces, wood moisture threshold remained below 12%, reducing the possibility of termite infestation and mold growth affecting wood framing.
  2. Insulated crawl spaces were drier than conventional wall-vented crawl spaces: the average relative humidity level remained below 70%.
  3. In drier climates, sealed crawl spaces managed standard moisture levels of about 50%, but ventilated crawl spaces maintained 70% relative humidity for several days at a time.
  4. Houses with insulated flooring and sealed crawl spaces saved about 20 percent in natural gas during the winter and an additional 15% annual energy savings compared with a control group.

What Is A Proper Crawl Space Humidity Level?

Keeping your crawl space at a constant 55% humidity level keeps the air healthy and the crawl space free from infestation. 

Check the humidity levels in your crawl space with an electronic thermo-hygrometer.  You can find a good one on Amazon.com for as little as $15. 

If your humidity is consistently above 65 percent, then it is time to do something about it.

Why is There Water in My Crawl Space?

what should the humidity be in my crawl space

There are several reasons water can get into your crawl space. 

You will need to find and correct these problems before trying to dehumidify or seal your crawl space.

Bulk Water Problems

Can you see a few inches or more of standing water under your home?

If so, check for plumbing leaks and drainage problems. 

A common reason of bulk water in the crawl space is incorrect sloping of the ground surrounding the house, causing water to drain under your home.

If the ground slopes toward your house; there is a problem. The ground should decline from the home at a 5% grade or more. The floor sloping down toward the base causes water to seepage into the crawl space.

Ground Moisture Evaporation

If the ground itself is filled with water, and it can evaporate into the crawl space air. 

Sometimes the soil appears dry but that’s because it is evaporating into your crawl space.

After using a thermo-hygrometer to measure the relative humidity under your home, you will know whether you’ve got a floor moisture evaporation issue.

Crawl Space Vents

Crawl space vents are an obsolete fix for humidity in a crawl space. 

When it is damp outside, vents only guarantee the crawl space air will be filled with moist air! This will not help with a moisture issue.

On a humid and hot summer day, air venting into the crawl space can be as much as 75% relative humidity and 85 degrees. 

If this hot wet air hits the cooler air of the crawl space, it will quickly raise the relative humidity – by about 2% per degree F.

This means that when the air outside is 10 degrees F warmer than your crawl space, the humidity under your home can go up by 20%. This causes condensation across the surfaces within the crawl space. 

During the winter, your crawl space dries out – but the vents waste a whole lot of heat, costing you money for nothing. 

What Solutions are Best for Reducing Crawl Space Humidity?

what should the relative humidity be in my crawl space

Fix Water Problems First

If there is bulk water in the crawl space, fix this issue first. 

When the outside ground slopes toward the base, re-grade the soil to ensure that the dirt slopes away from the foundation.

Do you suspect a plumbing leak? 

Get a skilled plumber to check the pipes under your home. Occasionally, old copper pipes have leaks as small as a pinhole. Over time, very small leaks add up to large water problems.

Install a Sump Pump

ISometimes, an outdoor and unfixable problem such as shedding water from the neighbor’s house is the issue. If that’s true, a sump pump is a great fix.

A sump pump uses a bucket dug into the ground in the crawl space to collect water from under your home and pump it back up into the yard. 

Any water that gets into your crawlspace drains down the graded floor and into the sump pump’s holding bucket. 

The sump pump then pushes the water up and into a safely-graded part of your yard where it will flow into the street or into another lot.

If you use a sump pump, check it two or three times annually to be sure it’s functioning.

Install a Vapor Barrier

A vapor barrier is a thick sheet of plastic that covers the floor of your crawl space. 

For those who have a dirt floor in the crawl space, a vapor barrier is a must.

A vapor barrier keeps moisture under the vinyl and away from the timber joists of your floor. Additionally, it keeps your insulation dry.

Use a professional to install a vapor barrier correctly, because a vapor barrier also protects the air you breathe in your dwelling.

Crawl Space Dehumidifiers

There’s one last step that is sometimes necessary for maintaining proper humidity levels in the crawl space. 

That is the installation of a crawl space dehumidifier.

A crawlspace dehumidifier is set up in the crawl space, positioned for optimum airflow. Its fan circulates clean air throughout the area. This keeps crawl space humidity levels down.

Benefits of Utilizing a Dehumidifier In Your Crawlspace

There are several advantages of using a dehumidifier in your crawl space:

Health protection. 

When you improve your home’s air quality by using a dehumidifier in your basement, you are helping to protect your health. 

If your house experiences relatively higher humidity, it can turn into a petri dish for mold and pests. 

With a dehumidifier in your crawl space, you can better control the moisture in your home..

Improving indoor air quality through moisture management can reduce and perhaps even prevent some symptoms of allergies. These allergies can be eye irritation, headaches, and respiratory troubles.

Pest protection.

If you’re able to control the moisture on your crawl space with a dehumidifier, then you also protect your home against insects. 

Controlling the moisture from the air reduces the chance of termites and other pest infestations. 

Termites are thought to cause more harm to homes than fires and storms combined…

what should the humidity level be in my crawl space

Maintain structural integrity. 

If relative humidity in your crawl space exceeds 70%, it most likely will create condensation. 

This dramatically increases the chance of wood rot in structural / support beams. 

Wood rot can be expected whenever moisture in the atmosphere is at least 28%, and it occurs rapidly when liquid water reaches wood.

If the wood in your crawl space gets damaged, there is a risk that the wood will no longer properly maintain the weight of your house. 

A dehumidifier in your crawl space will help protect your house from moisture-induced wood rot and structural failures than can occur from it.

More comfortable living. 

High humidity can impact your comfort by making you and your family feel hot and sticky. 

If you must use your AC to remove the humidity, then you end up spending more money and risk becoming too cold.

If you set up a dehumidifier in your crawl space, you can more easily manage the humidity levels in your home without relying on your air conditioner to make certain that you and your loved ones are always comfy. 

Energy efficiency. 

If you must use your air conditioner to eliminate excess humidity, you’ll end up causing your energy bill to go up – because air conditioners use a lot of energy. Using a dehumidifier in your crawl space rather than turning up your air conditioner will save money, net.

By following these suggestions, you can maintain the relative humidity level of your crawlspace at or below the recommended 60% in all seasons.

Keep your home healthy and give it a longer life of trouble-free care – by keeping your crawl space dry.

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