Signs of Mold in the Home / Indoor Mold

Indoor mold growth, whether visible or hidden, can cause a wide variety of problems for humans. If you see or smell signs of mold in your house, its important to work quickly before it literally grows out of control.


If you are having mold related health issues, can see mold indoors, and/or smell a musty odor, it's time to investigate. Left untreated, indoor mold infestation can cause damage to your home and belongings, and mold exposure has been linked to a plethora of health issues in humans.


Here are the perfect conditions for mold growth:


1.    Moisture content greater than 20 %
2.    Relative humidity above 60%
3.    Temperature above 68 degrees F

4.  Nutrient or organic material on which to grow (wood, sheetrock, paper, ceiling tiles, etc.)


So, keeping moisture, humidity and temperature under control will play a big role in preventing indoor mold. Read on to find out how.


Follow Your Nose!

Believe it or not, the most reliable method of finding the source of mold contamination within a building is often right under your nose! When you detect that familiar musty odor / mold smell, it means that mold is actively growing and releasing MVOC’s, or Microbial Volatile Organic Compounds.  MVOCs are produced as a metabolic by-product of bacteria and fungi, and are often detectable even before any visible signs of mold growth appear.  As a result, our nose can act as an early indicator of a potential mold problem and the odors can lead you directly to the source of contamination. Moldy odors should not be ignored, because even if it is hidden, mold will continue to grow until the issue is resolved.


Visible Mold

Obviously if you have visible signs of mold in your house and mold growth that you can see, then you know where to start your investigation. Even a few specs of mold on the wall can grow into a much bigger problem if ignored. It should be noted that if you discover a major mold problem or have signs of black mold in your home or workplace, you should not disturb the mold, especially if there are individuals with associated health complaints. Carefully peeking behind wall cavities is one thing, but removing a panel with six feet of contaminated wallboard covered in Stachybotrys in a home with an individual having respiratory complications would not be a wise choice. For mold infestation, you should always call a professional and get an expert opinion, preferably someone that is board certified.


Signs of Mold in the Attic

Attics contaminated with mold can usually be blamed, in part, on the familiar adage "hot air rises." Signs of mold in the attic are quite common in houses that have neglected proper ventilation protocol. Ideally, the hot air in a building will rise straight to the attic and, when properly ventilated, out into the great outdoors and beyond. But whether by ignorance or to save some time, some builders will actually cover the attic vents with tar paper or insulation. When they do this, the air has nowhere to go! Attic vents are designed to ensure proper air flow and this ventilation is absolutely critical; when vents are blocked, covered, or eliminated, mold and moisture problems result.

A second common situation observed in attics is when the bathroom or kitchen vents are vented straight into the attic. Releasing these vents into the attic, rather than outdoors, introduces very warm and humid air into an already warm space. Heavily concentrated mold growth is often found right around these vents in attics. If you suspect your mold problem is originating in your attic, check for proper ventilation and you may have your answer.  


Signs of Mold in the Basement

Basement mold is a widespread issue. Since basements are built below ground level, and the ground is very moist, moisture in the surrounding soil can permeate through the foundation and unless you take preventative measures, you may soon see signs of mold in your basement. When conditions are ripe (remember the moisture, humidity and temperature conditions listed above?) basement mold grows easily.

There are some precautions you can take to prevent basement mold (preferably before finishing off the area for living space) :


  • Thoroughly inspect walls, floors & ceiling for obvious cracks, holes, drainage problems or signs of moisture.
  • Immediately repair any problems found
  • Apply a good quality waterproof sealant to the floors and walls.
  • Invest in a dehumidifier and/or air conditioner to maintain proper humidity levels (must be kept below 60% relative humidity)
  • Invest in a hygrometer so you can check humidity levels.
  • There are contractors that specialize in “Basement Waterproofing”; certainly a more expensive way to go but a good option if you can afford it.


If you already have mold in your basement (or other area indoors) and want to know how to get rid of it, you can follow the some of the tips listed here.


Signs of Mold in the Bathroom

Bathrooms are another common area where mold is often found. Hot showers, soaking baths, running hot water at the sink, condensation on mirrors and windows, standing water left to sit... these activities all encourage mold growth. And as mentioned earlier, if your bathroom fan is not venting outside, or if you don't use the fan at all, you are likely going to end up with signs of mold in your bathroom. Here are some tips to help prevent bathroom mold:

  • Install a fan that vents outside, and make sure to use it!
  • Crack a window
  • Wipe up all visible water & moisture with each bathroom visit.


Water Events, Standing Water, Flooding & Mold

If you have signs of mold in your main living space, and you are sure that the problem is not originating in your attic or basement, then there must be some sort of moisture issue in the main living area. This issue may be known to you (an overflowing tub for example) or unknown (a leaking pipe in the wall cavity). These moisture issues are all called "water events," and resolving them is the key to stopping a major mold problem.


The first thing to do is to check all of your appliances, plumbing and pipes, and look for all possible sources of leaks or moisture problems.  Look for water stains and visible mold growth on all walls and floors. Also think about recent episodes of water invading your living area (overflowing sinks, water heaters, flooding, etc.). Many times people don’t know they have a problem with mold until they start to smell it. Other times the problem is much more obvious, like when you notice “black stuff” growing on your wall. Either way, appropriately removing the mold along with correcting the water intrusion or water source is your key to being mold free.


What to do if you find mold in your home or business?

For major mold infestations, we recommend you call professional, trusted, board-certified Indoor Air Quality company. But if your mold problem seems minor (a small confined patch of mold with no associated odors or health issues), you can try these remedies, one at a time or in combination with each other. They may do the trick.  


  • Remove and/or resolve any obvious/ visible moisture problems within 24-48 hours (wet carpets & sheetrock, leaking pipe, etc.).
  • Thoroughly clean visible mold with a household disinfectant (not bleach).
  • Remove excessive use of "house wrap" & insulation in the problem areas of your home
  • Open windows whenever possible
  • Use ventilation fans during showers and cooking
  • Use a dehumidifier
  • Keep the relative humidity below 60%.
  • If your building materials have been wet for more than 48 hours, call a Board Certified Specialist.

Check the following website for more information on how to find a Board Certified Indoor Environmental Professional in your area:


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