At What Humidity Does Mold Grow? Be Empowered!

You have bought a new humidifier, but you are hesitant to start using it because you are afraid raising the humidity will make mold grow in your house. But wait first… At what humidity does mold grow?

High humidity alone does not cause mold, as long as you don’t raise it excessively. Keeping the right humidity level prevents mold growth in your home.

This requires you to know the best humidity level for your bedroom, living room, and, indeed, any other room in the house.

In older articles, we saw just how nasty mold can be for your family’s health. We looked at the symptoms of mold exposure in children. It can leave you in dire straits!

We also looked at the warning signs of mold toxicity. Once again, nothing to smile about! Long-term exposure to indoor allergens like mold can lead to nasty health issues.

So, what humidity allows mold to grow? Humidity is not the only determinant of mold growth. There is a temperature and dew point. If the relative humidity is 95%, the dew point is 80, and the temperature is 85 degrees Fahrenheit, mold can grow in 2 days.

At what temperature and humidity does mold grow?

Mold will grow when the indoor temperature is between 77 and 86°F. When you are discussing the growth of mold in the house, you have to remember that temperature and humidity are the main growth factors for mold.

In high humidity and high temperatures, mold can grow really fast. Please look at the table below to see just what we mean.

Relative Humidity

Dew Point


Mold growth days

























As you can see from the table above, mold will grow faster when the relative humidity (RH) is high at 95%, the temperature is also considerably high at 80°F, and the dew point temperature is also considerably high at 78°F. In this set of conditions, mold grows in 2 days!

When the relative humidity is considerably low, at 82%, the temperature is at 75°F, and the dew point temperature is at 69°F, mold will take a longer time to grow, up to 9 days.

From this table, you can see that there is a clear relationship between fast mold growth, high temperatures, and high humidity.

You can get more information about how temperature, dewpoint, and relative humidity combine to create the perfect environment for mold from this web page.

In the same way that temperature contributes to the growth of mold, it can also help kill it. For instance, if the temperatures fall below freezing point, you will be rid of mold spores.

If the temperatures rise above 140°F, they will also kill mold spores. However, the question on your mind is: when the temperatures are that high or that low, where will you be staying?

At what humidity does mold grow in crawl spaces?

At what humidity does mold grow in crawl space

If the humidity level in your basement or attic is 60%, mold will start to grow.

Crawl space means the spaces that are under either the roof or the floor. In most homes, crawl spaces can be the most neglected spaces.

If you do not maintain the humidity at the right level in the crawl spaces, the high humidity will spread to the rest of the house.

The basement is one of the most notorious spaces for spreading humidity. However, to counter that, we brought you an article on the best dehumidifier for mould that you can use in the basement.

We also brought you an article on the best dehumidifier with a drain hose for the basement. These appliances can help you arrest runaway humidity in these spaces.

Always keep the humidity in the crawl spaces at 30 to 50%, or at the level that you are maintaining for the rest of the house.

Humidity escapes from concentrated places into dry air. Therefore, if the humidity level in your basement is higher than in the rest of the house, the dampness will find its way into your house.

If you have very high humidity in the basement, you can get a dehumidifier with a pump so that it can dispose of the water vertically.

Also, remember to seal your house properly because outdoor humidity will affect indoor humidity level.

What should the humidity level be under my house?

What should the humidity level be under my house

The best humidity level for any space that’s in your house is between 30 and 50% in summer. The air is warmer during this time, and warmer air holds more moisture.

In the winter, the best humidity level to maintain for all spaces is between 40 and 60%. Cold air is drier than warm air.

To prevent static electricity, dry and cracked lips, and other indications of dry air in the house, set the humidity level on your humidifier between 30 and 60%.

If you can feel comfortable in less, say 55%, it is even better. Remember, since you will be running the furnace to keep the house warm, mold might start growing if the humidity level is at 60%.

The best humidity level to prevent mold

Best humidity level to prevent mold

Now that you have an idea of the factors that cause mold growth, you might want to know the best humidity level to prevent the development of this indoor allergen.

Remember, high humidity makes dust mites thrive. It will also make mold grow fast in the dark spaces in your house.

When mold matures, it spreads spores. These spores float in the air to settle in other places in your house. If they find the right conditions for growth, bang! A new mold colony forms.

If you keep the air too dry, you will not have mold at home. However, you will experience the nasty symptoms of sleeping in a dry room.

Likewise, if the humidity is too high, you will experience the health effects of high humidity on the body.

Thus, you need to find a balance and maintain the humidity at just the right level. Always keep the indoor humidity level between 30 and 50%. During winter, you can raise the humidity some more, to about 40% at the minimum.

Keeping the indoor humidity level at 55% is considered okay; you know, you can live with that if the temperature is right.

However, anything above 60%, mold will start growing. Also, at 60%, you will feel very uncomfortable because of the dampness on your skin.

At what humidity level does mold stop growing?

At what humidity level does mold stop growing

Knowing at what humidity level mold starts developing is good, but so is knowing at what level it stops growing.

If you have mold growing in the house, it is important to lower the humidity level. Secondly, it is best to remove the mold already growing in your spaces.

If you lower the humidity level and neglect to remove the mold, there is a chance it can spread to other parts of the mold. As long as there are mold spores in the air, they can start new mold colonies.

Even with no moisture in the air, mold spores do not die immediately. They will just stay inactive for a long time. As soon as the humidity level rises, the spores will come alive again.

At a relative humidity level of 55% or lower, mold spores will stop making new mold colonies. However, they won’t die. It’s best to remove the spores from the air.

Final Thoughts

Humidity levels that exceed 55% encourage rampant mold growth in your home. To prevent this, keep your eye on the hygrometer or humidistat for relative humidity and dew point readings.

You can use a dehumidifier to lower the humidity in your house. Even better, you can install a whole house dehumidifier for yourself. It will lower the humidity level in the entire indoor space.

Remember to check your closets, crawl spaces, garages, and other spaces that we neglect so easily. Mold likes to grow in hidden spaces as long as there is warmth, moisture, and nutrients.

Please also read my past posts on:

Air purifier or dehumidifier for musty smell

Can mold cause sinus infection

Is Air Purifier Good For Mold?

Can Mold Grow At 60 Percent Humidity?

Can A Humidifier Cause Mold In Room?

Toxic Black Mold Vs Black Mold