Why Is There High Humidity in the House after Rain? 4 Main Reasons

Does rain increase indoor humidity? Yes, but hold that thought a bit. We will get deeper into this topic.

In another article, we looked at the relationship between rain and humidity. We discussed several things.

If you read it, you will see that it seems to rain when the humidity is high outside. When there is low humidity, there is just a little water vapor in the air.

At 90 to 99 percent, the clouds are too saturated and can’t hold any more water. They fall as rain.

So, will you experience high humidity in the house after rain? When it stops raining, water evaporates. Evaporation is the escape of moisture into drier surroundings. The dry air in your house absorbs the moisture from the rain, thus raising the indoor humidity. If you run the AC, or humidifier, or open the windows, the humidity might go down. If it does not, check for water infiltration.

Why there’s high humidity in the house after the rain

Does rain increase indoor humidity

The recommendation for indoor RH (relative humidity) levels is 30 to 50%. However, after rain, you’ll notice an increase in the humidity level. If you measure it with a hygrometer, you can record highs of 60% or higher.

If left unchecked, the humidity level will cause condensation on the windows and other surfaces. If you see such happening, it means the humidity is already too high. It can also cause mold and damage to your paint, books, furniture, and paintings.

Back to the topic, rain increases the humidity level outdoors and indoors. However, outdoors, the humidity level drops faster after the rain stops. The water vapor evaporates into the surrounding air faster.

Indoors, the humidity level increases and lingers much longer. There are a few reasons for this:

1. Hot air holds humidity longer

If the weather is cold, you will turn on the heat. This raises the warmth level indoors. Warm air holds more moisture as compared to cooler air.

When it starts raining and there’s an increase in indoor humidity, do not worry. Rain raises humidity levels outdoors and indoors. However, when the humidity stays high long after the rain has stopped, there could be a problem.

If the air in your home is cold, it will not hold much moisture. Since the air outside will drop the humidity level faster, open the windows. This will enhance airflow inside and help lower the moisture level.

When damp air gets warm (as it will when you turn on the heater) moisture, the moisture converts to the gas state faster and increases the number of water molecules in the air.

Cold air is denser. It has less room to hold water molecules. Therefore, when vapor comes into contact with the cold, dense air, it condenses, turns into dew, and drop on the surfaces.

2. It is humid outside

If you have high humidity outside, you will also have humid air indoors. Thus, the house gets humid when it rains.

This is reasonable. In the summer, there is high humidity in most places. The air is hotter, so there is higher evaporation, and the air feels damp.

However, you can lower the humidity level indoors by turning on the AC or running a dehumidifier. If the humidity level outside is high, opening the windows and doors might not help.

It is better to switch on the humidifier to draw moisture from your indoor air.

3. You live in a place that is humid throughout the year

If you live in a place such as Florida that is humid throughout the year, rain will not make the humidity level any lower.

Since humidity is the amount of moisture in the air compared to the total amount it can hold at saturation, rain just adds more moisture. Therefore, the humidity level increases indoors and outdoors.

If you live in Austin Texas, which sometimes has an average humidity level of 90%, rain will make the air damper.

You might need to keep the whole house dehumidifier running throughout the year. In such a place, the humidity will increase indoors and stay high longer if it rains.

4. You have water infiltration in your home

Too high humidity after rain, say, long after the rain is gone, could mean that you have water infiltration at home.

When it rains and the water finds its way under your house, it will raise the humidity level. You can attribute this rise in humidity level to the rain since it caused the infiltration.

Have a professional look over your house to ensure it is completely sealed.

Does rain increase indoor humidity? FAQ

High indoor humidity after rain is quite common. However, it is good to know why this happens so that you can know how to control the humidity level in your space. Here are a few frequently asked questions to teach you more:

Does outside humidity affect indoor humidity?

There is constant airflow from and into the house through windows, doors, and ventilation. If the air from outside is more humid, it will affect the air indoors. You can close the doors and windows to control your indoor humidity.

Can it rain with low humidity?

As long as the clouds get to 100% humidity (saturation level), they will rain. If there is a lake in a desert, it can help rainfall in the desert because of evaporation.

So yes, it can rain even when the humidity level is low. Another thing is that when it rains, the clouds are at almost 100 percent humidity. The surrounding air has much lower humidity. So the rain falls into the low-humidity surroundings.

Also read: Humidifier sickness symptoms to watch out for

What is the humidity during rain?

The humidity level is usually 90 to 99 percent when it is raining. At this level, the water vapor condenses to form visible clouds after coming into contact with cold air.

The droplets become too heavy to the point where the air cannot support them anymore. They drop to the surrounding air and ground as rain.

Does 100% humidity mean it’s raining?

Not all the time, but since this is the level at which the water vapor gas has turned into water, there will be dew on the ground and other surfaces. As the air gets thinner and colder as you go up, heavy clouds (high humidity) might not rain.

Image of house gets humid when it rains

Conclusion: Humidity after rain

Does humidity rise when it rains? High humidity outside means high humidity inside. However, it should drop after the rain stops, or at least the following day, when you open the windows.

To prevent the development of mold colonies and other moisture damage in your house, run a dehumidifier. It will keep the humidity level at 30 to 50%.

When it rains, the humidity level will rise both outdoors and indoors. However, after a rainstorm, the outdoor humidity will drop faster because there is drier air, so the water evaporates faster.

Indoors, it is different because of the enclosed spaces. Once the dry air indoors absorbs the water from the rain, it takes a bit longer to lose it. Thus, it becomes more humid after it rains.

If you need a dehumidifier to lower your indoor humidity level, order the Waykar Dehumidifier rated for 2000 Sq. Ft on Amazon.com. It is perfect for basements and large rooms.