Mold Remediation Blog

Why Does Mold Flourish In The Dark?

And Does Light Destroy Mold?


Mold is an unwelcome visitor to all DC area homes, but it doesn’t become a real problem until it decides to stay and set up shop. Mold can affect your family’s health with a wide range of symptoms and can even harm your pets. Many homeowners think that mold only grows in the dark areas of their homes, but that just isn’t true.

How Mold Grows

While mold is most easily found in darkened areas of a home, it isn’t flourishing because of the darkness itself. It’s more about what darkness allows that light often takes away.
Mold needs the same things to survive that all life requires: food, moisture, and oxygen. Food is provided by anything organic — and mold isn’t picky. Wood and sheetrock are all it needs to get by. While mold needs oxygen to grow, it doesn’t need very much. Attempting to remove mold by limiting the amount of oxygen in a room doesn’t work. Unless you create a vacuum, there’ll be enough O2 in the air to keep mold fat and happy.
However, moisture is the one requirement it can’t skimp on. No moisture: no mold. Though, again, mold is good at doing a lot with a little.
High humidity (55%+) is enough moisture to keep mold healthy and growing. That’s why even a tiny water leak can cause massive mold growth in as little as 48 hours. You give mold a high level of resources, and it will go into exponential growth until it outgrows its water supply.

Mold In Light

While mold seems to like cold, dark spaces, it actually grows best in areas that are between 77 and 86 degrees. So, if you keep a light on in your basement, the chance of mold growth actually increases as the bulb heats the air. If the temperature dips down to below 40 degrees, mold will go into stasis, but it won’t die.
Standard light bulbs don’t create enough UV light to kill mold or its spores. And the UV light systems that ducting and HVAC companies will sell you are often ineffective because the mold isn’t exposed to the UV rays long enough to suffer any lasting harm.
Direct sunlight will, of course, kill mold, which is why you don’t see mold growing in areas that are open to the sky. But you will see mold growing in areas that enjoy even partial shade.
That’s why you can see mold growing on the shaded area of a poorly maintained roof. While sunlight is reaching the entire roof, it isn’t direct light where there is shade, and that’s all mold needs to survive.
Another factor is that diffuse light is less efficient at causing evaporation, so moisture clings to the shaded area of the roof long enough to give mold a water source. Morning dew is more than enough to keep mold going throughout the day.

So How Do You Stop Mold?

There are varying schools of thought on how you prevent mold growth. One popular opinion is that the more ventilation, the better. The idea is that, with enough air moving around, evaporation is encouraged, leaving the mold nothing to drink.

The max ventilation concept works well, right up until you realize that some areas have high humidity. That means that, instead of limiting moisture, all that hot, heavy, water-laden air moving through your crawlspace is creating a mold buffet. This is why the airy open floor plans of homes in Hawaii do nothing to help prevent the rampant mold growth Hawaiian Islanders deal with day in and day out. Even their electronic devices grow mold inside them, despite having cooling fans moving the air around constantly.

Controlling Humidity

The only sure-fire way to stop mold from growing in your home is to keep it dry with humidity levels between 30 – 50%. You can achieve this goal by using a properly fitted HVAC system in your home and dehumidifiers for your basement or crawlspace.
Air conditioning is about more than cooling your home. Using an HVAC system designed for the size of your home is key. Equally important is its ability to pull moisture out of the air, and if your system is too large, it won’t have enough time to dry your air before it reaches your preferred indoor temp and shuts off.

Basement Air

Basements, by design, aren’t good at exchanging air with the rest of your home, so don’t get the benefit of having the air dried by your HVAC system. To keep your basement dry, make sure that moisture isn’t coming in through the walls and add dehumidifiers, if needed, to keep the humidity down.

Crawl Spaces

Crawl spaces are where the ventilation argument really gets heated. If you live in a high humidity area, ventilation isn’t enough. Your best bet is to seal your crawl space completely, including the ground, and install a dehumidifier and small sump pump to get rid of any moisture that manages to sneak into the space.

A Final Word

So, does mold need darkness to grow? No. All it needs is protection from direct sunlight to thrive. The only practical way to eliminate mold growth is to keep all areas of your home below a maximum of 50% humidity. How you achieve that depends on your home and where you live.
If you think you might have a mold problem in your DC area home or want to ensure that you never will, contact us at Valor Mold for a free estimate.

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