A crawl space is a convenient area for HVAC installations and other sorts of piping. In addition, it helps improve the air quality by serving as a buffer between your house’s main floor and the ground underneath.
All the same, it needs as much maintenance as the rest of your property. Part of that is keeping the humidity levels in check.
This begs the question, can crawl space humidity be too low?
High humidity can be damaging, but low moisture levels are equally problematic. Why this is so will be discussed further in the following sections, so keep reading!
A crawl space draws out moisture from the earth, so it’s easily affected by changes in relative humidity (RH). When it reaches or goes beyond 55% RH, there’s a high chance of mold growth.
If left unchecked, it hastens wood rotting and can damage the structural support of your crawl space. So, you must make sure to dry out the area if you notice musty smells and black spots on surfaces.
Nevertheless, stay keen on how low moisture levels get, as this is also potentially damaging.
Wood is hygroscopic, so its water content varies with its surroundings.
When the air around it is too dry, wood releases water, causing it to shrink. Conversely, it absorbs moisture and expands if it gets too humid.
That said, frequent and extreme humidity changes can damage your home’s foundations.
Much of the air that goes into the main house comes from the crawl space, so keeping it clean and high-quality is essential.
Air that’s too dry poses health risks from bacteria and viruses that thrive even in low moisture levels. Examples of these microbes are Bacillus subtilis and the flu virus.
Such contaminants can cause dry skin and itchy eyes, throat, nasal passages, and other infections.
A crawl space is prone to dampness due to its location and possible pipe leaks. Ideally, you should maintain relative humidity between 30–50% and make it as stable as possible.
If the space gets too damp, you need to get to the bottom of it fast. Then, you can make the necessary adjustments.
Most often, the solution is better air circulation. For that, you can install a dehumidifier system to draw out and dispel excess moisture from the air.
Dehumidifiers come in a range of capacities and purchasing the wrong unit can prove ineffective.
To help you decide what’s best for your crawl space, first, you’ll need to have a target relative humidity. Afterward, you’ll have to gather the necessary information for your calculations.
Suppose you have the following data:
- Regular relative humidity: 80%
- Target relative humidity: 30%
- Temperature: 86°F
- Area of crawl space: 300 square feet
- Height of the crawl space: 3 feet
- Vapor pressure: 760 mmHg
Now, proceed in approximating the dehumidifier’s capacity through these steps:
- Convert the relative humidities to absolute humidities using an online calculator.
80% RH = 0.001498 lbs/ft3 (0.024 kg/m3)
30% RH = 0.000562 lbs/ft3 (0.009 kg/m3)
- Get the difference between the absolute humidities above.
0.001498 – 0.000562 = 0.000936 lbs/ft3 (0.015 kg/m3)
- Calculate the volume of the crawl space:
Volume = area x height = 300 sq. ft x 3 ft = 900 cubic feet
- Multiply the values from steps 2 and 3 to get the amount of water per hour.
0.000936 x 900 = 0.843 lbs (0.382 liters)
- Compute the required capacity per day.
0.382 liters per hour x 24 hours = 9.17 liters = 19.38 pints
Based on the calculations above, you’ll need a dehumidifier that can remove around 20 pints of water per day. However, don’t cut it too close to the unit’s specification to account for efficiency losses.
You may also experience extreme fluctuations in temperature and humidity from time to time, so keep that in mind as well.
The key to an efficient dehumidifier is maximum airflow, so installing the unit in the right spot is essential.
Typically, you’d want it in the middle of your crawl space to provide optimum coverage. Yet, if you know the source of humidity, that’s also a good place to start.
Just make sure there are no blockages to the discharge airflow when you decide on a side installation.
If there are dead spots or tight spaces, you can add a fan to keep the air moving. This way, more humid air reaches the dehumidifier.
Something else to consider is accessibility. You should avoid setting up in a hard-to-reach area at all costs.
That’s because you’ll need to clean the dehumidifier once or twice every 2 weeks so it continues to work efficiently.
If your equipment isn’t maintained properly, molds and bacteria can grow on it and shorten its lifespan.
Additionally, a dehumidifier creates a lot of noise that may seep through to the main house. Hence, look for a spot that’ll make the sound tolerable.
Lastly, choose a location that allows for proper drainage. Poor drainage can lead to complex issues such as clogging, leaks, and microbial growth.
Dehumidifier systems feature one of two drainage mechanisms:
Gravity drainage through a floor drain is your first option. This allows the continuous release of water away from the crawl space through a hose.
However, that only works if you have the unit installed in a more elevated area than the floor drain.
Generally, there should be a drop of at least a quarter of an inch for every 10 feet of run. If there’s not enough drop, the water can easily come back up and flood the space.
If that happens, you may face the same moisture problem you’re trying to avoid. So, carefully study this aspect before installation.
To add, ensure that the drain channels water at least 2 feet away from your home’s foundation. Even better if it’s on a slope so it drains faster.
In the absence of a floor drain in the crawl space, the best option is to use condensate pumps.
Some high-capacity dehumidifiers have built-in pumps and drain hoses that automatically discharge condensates.
For a unit without this feature, you can purchase and attach an external pump to the setup.
The advantage of condensate pumps is that they’re able to pump the water as far as fifteen feet away. This also gives you flexibility in directing where to drain the dehumidifier.
Can a crawl space humidity be too low?
The relative humidity in this area of your home can’t be too high or too low. Ideally, you should maintain it between 30–50%.
To help you manage the crawl space, you can use a dehumidifier system. Install the unit in an unobstructed area where there is maximum airflow.
Additionally, make sure that the dehumidifier has good drainage and is easily accessible for cleaning and maintenance.
Taking these necessary steps not only prevents damage to structures but also keeps the air you breathe clean and safe.
I have a bachelor’s degree in Computer Information Systems and over 10 years of experience working in IT. As a homeowner, I love working on projects around the house, and as a father, I love investigating various ways to keep my family safe (whether or not this involves tech). I’ve also played guitar for almost 20 years and love writing music, although it’s hard to find the time these days.