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  • Joshua Leviton

5 things to know about the mold around your windows or on your general items.

A large portion of my clients call because they see “black mold” around their indoor windows. Though this is mold there are a few things to know about it that might save you some money and peace of mind.


1. The toxic mold type commonly known as “black mold” is actually called Stachybotrys. The most important thing to know is that Stachybotrys is not the only black mold. The mold type most commonly mistaken for being Stachybotrys in my experience is called Cladosporium. Cladosporium is a plant pathogen that is generally harmless unless a person is specifically sensitive or if there are extremely elevated levels in a home. This is often the type of mold you will also find growing in your shower/bathtub grout. So if you see black mold growing you don’t need to panic, look up general pictures of Stachybotrys and of Cladosporium and see if the mold you are seeing look like one or the other.

2. Stachybotrys is a slower growing mold type that needs a significant amount of moisture. The vast majority of the time I only see Stachybotrys growing when there is a leak and drywall or wood has been saturated with water for at least 72 hours, usually longer. However, that being said, I can’t claim this is 100% true, this is just in my experience. Many other mold types such as Cladosporium can simply grow when relative humidity levels get to high, usually above 70%.

3. If you see condensation on your windows that is the most obvious indicator that relative humidity levels are too high. This means that air molecule are holding a lot of water and when the cold air from inside and the hot air from outside, or visa versa, meat at the window, it condenses and you get water on your window. This is the most common scenario I see and when I walk into an inspection and see mold growing around windows and on people furniture or clothing I know it is an elevated relative humidity issue. However, this does not mean there is no leak, it could be that there is a leak in the crawl space or in the wall that is evaporating and raising the relative humidity indoors. So just because we can likely attribute the visible mold you are seeing on the widows and/or clothing to humidity, it does not mean there isn’t also possibly a leak somewhere.

4. The mold around your windows and possibly on your walls is usually surface mold and can be cleaned off with household cleaners or bleach. However, it is possible that it has grown into the pores of the material and needs to be cut out to completely get rid of it. Sometimes this is necessary and sometimes cleaning it off is good enough. If you cleaned it off and kept the relative humidity levels low enough and it doesn’t grow back, problem solved. Though if you clean it off and it grows back, cut it out and replace the materials. When mold is growing on your items you will likely see several kinds of mold. On furniture I usually see one of two or both allergen mold types called Penicillium or Aspergillus. These types can cause respiratory issues and when you have mold growing on your furniture or clothing in my opinion you should just dispose of it. See my article about cleaning mold call cleaning mold 101 for further advice about what to do.

5. Keep relative humidity levels low and periodically check for any leaks and you may be able to prevent a mold problem before it starts. Sometimes a residence is just built in a way where there is no airflow or ventilation and you are going to experience some mold growth. But many times you can prevent it by taking a few precautionary measures. The most common cause for elevated humidity levels is showering. You are directly putting moisture into the air in the form of steam when you are showering so of course the best thing you can do is open windows and run the ceiling fan in your bathroom while you shower to vent the steam. If that isn’t doing enough you can run a dehumidifier and that should remove large amounts of water from the air for you. Depending on where you live you will be emptying buckets of water daily sometimes and will be surprised at how much moisture is in the air. I also suggest purchasing a relative humidity meter and a moisture meter. These tools will assist you in keeping relative humidity levels in an acceptable range as well as give you a way to check if there is moisture in walls.


Preventative measures are the only way to lower your chance of needing to deal with mold problems. In the end though, not all mold is horrible, we are breathing it in at all times because if you didn’t already know, the outdoor air is full of mold spores at all times. I always recommend running a HEPA air filter in your home because it will improve the air quality in general and just in case you have some undesirable mold growing it will catch those mold spores as well.

So if you see mold, don’t panic, either call a mold inspector to get it checked out and tested or do some research of your own so you have more information before deciding what to do. I always recommend calling a mold inspector or specialist because though testing can be expensive sometimes its necessary and your inspector should know when to test and when not to. Many times a mold inspector won’t be able to tell exactly what mold type it is from visually looking at it so testing is sometimes necessary. That being said, the main job of an inspector is to check if mold exists even when it is not visible and this will remain our primary role. But in the end, advice is always free, at least from me it is so give me a call.


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