What Is mold and where did it come from?

What is it?

Visible mold growth might seem like an obvious sign of mold. However, many people don't notice small amounts of mold growth or they think it's just soot or dirt.

If you can see mold growth, even if it's only small, you should take action immediately. Even small mold patches can spread really fast and the fact that there is any mold serves to show that the conditions in your home are right for mold to grow. Mold needs these conditions before it can begin to grow:

  • Mold spores
  • A food source (eg wood, drywall, cotton)
  • Darkness (mold can't grow under ultraviolet light)
  • Warmth (mold can't grow in freezing temperatures)
  • Oxygen
  • Moisture (eg water leaks, humidity)
  • Enough time (most molds can begin to grow in 24-48 hours if the conditions are right)

Moisture is really the key cause of mold growth since the other conditions on the list are always going to be present in homes.

So, essentially, the difference between whether mold grows in your home or not comes down to whether you have a moisture problem

Where did this come from?

  1. Humidity
    • If the weather's been very humid for a few days in a row you might notice mold starting to grow in your home. When it rains for several days it's especially common to see mold start to grow on walls, benches and other surfaces because of the wet air.

      If you live where humidity in the air is naturally high, like by the coast or another large body of water, then mold growth in your home can also be a recurring problem.

      Also when moisture inside your house evaporates into the air it increases the humidity indoors. If your home isn't well ventilated then the humidity will stay high for a long time.

      Drying clothes indoors on clothes lines or stands is a common culprit when it comes to causes of indoor humidity problems. The household HVAC system can also create humidity troubles while it artificially heats or cools the air.

      Sometimes people use humidifiers in their homes. But there are molds that only need the humidity level to be higher than 55% to start growing. So if you need to use a humidifier in your home make sure to keep the humidity below 55%.

      Not only does high humidity feed mold, but it means that puddles of water and damp materials in the home take longer to dry out. These wet surfaces can in turn create mold growth of their own.
  2. Leaking Pipes
    • Water leaks from pipes are a common cause of mold growth. The worst leaks are the ones that go undetected because they are hidden out of view, like inside a wall. By the time you discover these leaks mold has usually started to grow already.
  3. Leaks in Roofs
    • Like some leaking pipes, a roof that leaks into the attic might not be discovered until it's already lead to mold growth.

      The best thing to do is to check the attic regularly for leaks and keep an eye on the ceiling below the attic. If you notice any signs of water damage on the ceiling or any mold that has grown through then you probably have a leaking roof.
  4. Condensation
    • Cold surfaces can create condensation in your home. Condensation collects on cold metal pipes as well as on cold concrete floors, even if there is carpet over the top, and on walls. Places like these where condensation occurs are prime spots for mold growth.
  5. Poor Ventilation
    • If your home is poorly ventilated it can create pockets of stagnant moist air which mold thrives in. Steam and water evaporating into the air creates humidity inside which then needs to be circulated outdoors through windows to keep the moisture level balanced.

      Poor ventilation also means wet surfaces dry out more slowly. Ventilation is especially important in rooms such as the bathroom and the kitchen where there is a lot of steam
  6. Flooding
    • It is almost inevitable that some mold problems will develop after your home has been affected by flooding. Obviously your house will be very wet for a long time during a flood, taking days or even weeks to dry out. Since mold only needs a suitable surface to be wet for 24 hours before it can grow this means there is a huge risk of mold growth.

      Some dangerous toxic molds require more extreme conditions than common molds do, such as the toxic mold Stachybotrys chartarum which requires material to be very wet for several days to grow. A flood can create these conditions putting your home more at risk of being infested with dangerous toxic molds.
  7. Dam Basement
    • Basements often contain higher amounts of moisture or humidity than other rooms because they are usually not well ventilated. Basements are also often colder meaning more condensation occurs which leads to dampness and humidity.

      Also any water from leaks in your home will often end up running down to the basement since it is lower than all the other rooms. Not only is mold more likely to grow in basements but because they are usually neglected mold growth may not be discovered until it is well set in.
  8. Water at the houses’ foundation
    • Water building up in the yard and ground around the base of your house can cause frequent water problems for the foundation of your home.

      If the ground around your home slopes towards the house rainwater will end up building up at the foundation. If this causes constant problems you might even need to do some landscaping to modify the slope of the ground so water drains away from the house. Alternatively ditches and drains can be dug to channel water away from the home.


      If you don't take care of mold it will soon become a bigger problem. Visible mold growth could also be a sign that there is a much larger mold colony growing hidden away from view.

      Sometimes you might not realize there is mold in your house, especially if it is unusual looking mold. Some mold growth looks white and thread-like. Other mold appears as clusters of small black spots. Mold can be black, gray-brown, gray-green or white in color.

      Decisions about appropriate remediation strategies are not always reliably made based on visual inspection alone. “Hidden mold” is mold growing in places not readily visible such as on the reverse side of wallboard panels and in HVAC systems.