Finding Mold In Your Home

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You Smell Mold Or Have Reason To Believe Your Are Exposed To Mold

So you think you smell mold and you are looking for the source. Where do you look and how will you recognize it? That is what we will consider in this article.

If a building smells moldy, you may suspect mold even if you can't see it. You may suspect mold if you know there has been a moisture problem in the building and its occupants are reporting health problems. Often what is smelled is actually being emitted from bacteria that are also growing on these materials and competing with the mold. Building materials may release smells as they are broken down also. All of this may be toxic and have health effects. Unfortunately, you can have mold and it may not be associated with any smells and makes people think there is no mold.

Visible And Invisible Mold

The physical inspection of the building and the items in the building is the most important assessment to make. You can look for visible mold, but you can also look for signs of mold. The most common sign of mold is water or moisture on building materials or on objects in the building. Look for any evidence of moisture or dampness on the inside of the building anywhere.  Even old water stains on the wall, ceiling, flooring etc. can lead you to mold. It is not just fresh mold that can cause health issues, there could have been a leak in the wall years ago and someone dried it out after it started to grow mold, but did not remediate the area. That area will often have old mold, mold spores and mycotoxins as well as other toxins left in the cavity. These toxins and toxin fragments are small and end up outside of the wall cavity in the air and dust and can cause health consequences, especially in susceptible people. Some toxins are volatile organic compounds that easily volatalize into the air over time. They can go out into the environment and adsorb into other building materials or furnishings.

The first thing to cover on your venture to find mold is how to protect yourself while looking for mold.

Avoid Mold Exposure

  • Do not touch mold or moldy items with your bare hands.
  • Do not get mold, mold spores or mycotoxins in your eyes, or on your skin.
  • Avoid breathing in mold, mold spores or mycotoxins.
  • Consider using personal protective equipment (PPE) if disturbing mold during a home inspection, assessment, or walk through. The minimum PPE is an N-95 respirator (available at most hardware stores), gloves, and goggles. The ‘N95’ designation means that when subjected to careful testing, the respirator blocks at least 95 percent of very small (0.3 micron) test particles. If properly fitted, the filtration capabilities of N-95 respirators exceed those of face masks. However, even a properly fitted N-95 respirator does not completely eliminate the risk of toxins getting through the mask. The N-95 mask is not very helpful for water-damgaged homes as many of the toxins there are smaller and get through the mask.
  • Always remember to protect your health and safety as well as other occupants.


Areas To Check For Mold

  • attic
  • roof leaks
  • poorly installed roofing
  • crawl space
  • around windows
  • around doorways
  • bathroom tile and grout
  • kitchen tile and grout
  • leaking appliances - dish washer, refrigerator, freezer, ice maker hook ups
  • basement walls
  • basement floors
  • continous concrete foundations
  • around and under sinks, showers, tubs
  • shower drains that are broken may leak around the edge of the drain
  • doorways
  • outer walls of the building
  • improperly sealed chimney or broken seals
  • improper flashing or lack of flashing on roof or around windows when necessary
  • foundation of the building
  • sloop of building leading to water accumulation under concrete slabs
  • cracked cement slabs
  • all visible plumbing
  • slow leaks in plumbing fixtures
  • humidification systems - these are just dumb in most buildings - big mold grower
  • hvac systems - especially have the evaporator coil examined
  • sprinkler systems
  • Consider any area of construciton where you believe moisture may get trapped and be hidden: examples would be concrete slabs, wall cavities and floor cavities.


Check your caulking for areas that are old and dried up that may no longer be keeping moisture at bay. Caulking is on the outside of your house around all the openings. This would include the doorways, windows, openings in the roof for skylights, fan exhausts etc. Inside you will find caulking around your kitchen sink, the bathroom sinks, tubs, showers, tile in bathroom etc. Check all caulking everywhere.  It is there for a reason and if it is no longer working, it should be replace immediately.

What Mold Grows On In Buildings

  • wood
  • wall paper
  • insulation
  • fiberboard or sheetrock
  • cloth
  • paper
  • HVAC system - especially have the evaporator coil examined
  • any organic substance in the house
  • any place there is moisture


Tools That Can Be Useful In Your Investigation

Your eyes and sense of smell are usually  your best tools. If you smell something, but can't see it, keep looking and add more tools as it is there somewhere.  Sometimes your eyes and nose are not enough to find hidden moisture. Your eyes often miss mold as it is too tiny to see until it forms large colonies, plus mold is often behind a wall or other barrier. Some people are not able to smell the volatile organic compounds and you may also have contamination without volatile organic compounds. In these situations using tools to find moisture or to look inside of a wall can be helpful.

Trust You Nose If It Smells Musty

Some people claim that only actively growing mold produces smells. The people who say this, apparently have never had this issue and/or have poor olfaction. Many of us not only can tell if there is active  mold growing, but we can tell when there is a past mold activity that is no longer growing. The fact is that both of them make those of us who are sensitive sick. You learn to trust your sense of smell really quickly. It is important to point out that these smells are not just from the mold, but also can be from bacteria growing in competition with the  mold, as well as toxic breakdown products of the building materials as the mold and bacteria consume those substances. There is a varitable soup of smells that can exist and  many of these smells remain even when the moisture and the growth is long gone. The smell can change, but is still recognizable.

Another important point is that even at suboptimal conditions for growth, production of fungal volatile organic compounds can be significant.

Many of us find that when we go through the process of removing mycotoxins and other toxins from our body, that our sense of smell increases and becomes more refined.  In fact, often people who are most overwhelmed and sick from CIRS or mold illness are least able to smell the toxins bothering them.

Testing For Mold Spores

For this data, please read the article on "Testing A Moldy Building".

Moisture Meters

Many investigators use moisture meters to find wet areas where mold may be growing. These meters measure the moisture in many types of building materials. They also can monitor the process of drying these materials. A moisture meter typically has a thin probe that can be inserted into the material to be tested or pressed directly against its surface. Moisture meters can be used on carpet, wallboard, wood, brick, and concrete. Because mold often grows where moisture is high, a moisture meter can help an investigator locate hidden areas of mold growth. They mostly work, kind of like stud finders, mostly work. If moisture is detected a borescope can be used to look behind a wall.


Infrared Thermal Imaging

This tool can scan areas of wall surface looking for moisture that is behind it. It works by looking for cooler and warmer areas. Wetness in the wall begins evaporating as soon as it is on the wall. The evaporation cools the area and the camera sees this cooler area. Other things like cool air from a window can also create cool spots, but the person using the meter should be trained to know which cool spots are more likely due to a leak. This is a good tool to give you an idea of possible issues without opening the wall. Next you can look with a borescope or open the wall to peak.



Some investigators use borescopes to look for mold growth behind walls without significantly damaging the drywall. (A borescope is an optical probe, inserted through a small hole drilled into a wall, that lets an investigator inspect a small portion of the wall without causing extensive damage.)

Remember that you can also have mold in a wall cavity that was caused by a leak from long ago that has been fixed but the mold and mycotoxins are still there since it was not remediated properly. This could be what you smell and old pieces of mold, spores and mycotoxins can make you sick no matter how old they are. They are also tiny and can get outside of  wall cavities and cause health problems.



High humidity in a building can lead to mold growth, so humidity gauges may be useful for checking or monitoring humidity throughout the building.

A relative humidity gauge that tells you how much moisture is in your house can be found in an electronic gadget store. This is one I have used and had good luck with. (If you purchase from this affiliate link, I receive a small commission at no cost to you.)


Any part of a building that is below the ground level will be more likely to have moisture issues. Check the basement carefully for signs of moisture and mold. It is thought that heating basements to 60 degrees will keep condensation from forming and be less likely to feed a mold problem. However, my suggestion would be to stay away from below grade spaces like basements. If I did have a basement in my house and suspected there may be mold there,  I would put a dehumidifier in it to see if I had much moisture in the basement. If I did, I would next find out where the moisture was coming from keep the dehumidifier going to lower the overall humidity. Often the cause of the moisture is coming from the walls and is ultimately caused by something going on outside in the ground around the house or outside in the construction of the house. A common issue is inadequate drainage around the perimeter of the house, a gutter or downspout issue, a wall leak or other similar issue. Look at the walls, the roof, the gutters/downspouts and all around the perimeter of the house. Is the soil sloped towards the house? If so, water will be brought towards the house from the surrounding area. This needs to be changed or if you can not change it, a drainage system must be put around the house to drain the water away from the house.  If the house is at the base of a hill and the moisture coming off the hill is not being routed away from the house with a drainage system, again a drainage system must be installed. These issues can be resolved by fixing construction or adding drainage.

A well built house will have a large roof overhang which will be very useful at keeping water away from the sides and even the bottom edge of your house.

Carpet In The Basement

I would definitely not put a carpet in the basement of anything else that readily grows mold. If there is carpet in the basement, look under it for a possible source of mold.

Covered Basement Walls

Basements should not have anything against the concrete walls as this can build up moisture behind the insulation, wallboard etc and grow mold. If there is anything attached to the basement wall, look carefully at it for moisture. Generally wall coverings on basements are not too thick and if you suspect a problem, you may be able to pull a piece of wall covering off and simply look. Also consider using a moisture meter.


Concrete floors/slabs

The concrete that we use tends to wick moisture into it. Building biologists claim the old style concrete of magnesium oxide actually expells moisture. If you have a concrete floor or foundation slab, the theory has been that it needs to have some type of liner underneath it to keep moisture from wicking up via the ground into the concrete. However, the building biologists claim that mold grows between the moisutre barrier and the concrete as well as underneath the barrier.

Consider this if there is a concrete slab and you ruled out other areas. To find out if moisture is coming up through a concrete slab, simply leave a piece of plywood or similar object on top of it and check it out in a week to see if there is moisture on the bottom of it.

Crawl Space

This is often an area that may be the cause of bad, moldy air in your home. Look carefully in the crawl space and look underneath insulation and vapor barriers.

Most crawl spaces are vented. However, the new thought is that conditioned crawl spaces are a better way to go. I am not so sure about this. Some people have had trouble with these.

Crawl spaces should be designed and constructed to be dry. Crawl spaces should control rainwater, groundwater and provide drainage for potential plumbing leaks or flooding incidents. Some people are conditioning a crawl space by heating and cooling the crawl space as if the crawl space is included as part of the home. Air must be supplied to the crawl space from the home in order to provide this conditioning. Although some contractors suggest returning this air back to the home, I would have it exhausted to the outside unless I was assured by the encapsulation system in the crawlspace that there was no way there would be any type of mold laden air in the crawl space returning to the inside of my home. Ventilating the air to the outside could get expensive. If the air was not being returned to the house, this could be a helpful method to decrease mold in the crawl space. However, the air is usually returned to the house due to cost, which could be hazardous.

Crawl spaces must have a ground cover or vapor barriers that prevents evaporation of ground moisture into the crawl space. One of the most common is 6 mil sheet polyethylene that has taped/sealed joints and that is attached to the crawl space perimeter walls. This ground cover must be continuous through piers and supports. However often this is not the case. There are some encasements that are being used and an example is this one called CleanSpace which appears to be a solution to moist, moldy air in crawl spaces getting into the house, but some people react to the materials Clean Space and other companies use and have said it caused a new toxic smell in the house that was not there previously.  Many types of vapor barriers are going to smell when they are first laid down.  (There are poor choices for building supplies, although this is starting to change.) There are various types of spray on materials being used now from wtaewr proof polymers to mixtures of magnesium oxide and clay that are sprayed on the building materials in the crawl space along with laying down a vapor barrier over soil.

Crawl space perimeter walls, steps, rim joist areas and any other concrete or exposed masonry has been insulated in the past to prevent moisture in the air from accessing these surfaces and creating condensation. However, sometimes the insulation material itself has traped moisture underneath or behind it. I think the idea of spraying magnesium oxide/clay sounds like it might be more beneficial. I am not a building biologist though and I suggest you consult one.

For more details on conditioned crawl spaces check out this link. Also see the vapor barrier section below.


Drywall, or sheetrock, or gypsum are a mold inclined material waiting for moisture. Drywall will swell when it is wet and become discolored, this makes it easier to look for damage. Leaks behind walls must get bad enough to keep the wall wet before you will notice an issue in drywall. A small leak behind drywall can go on for some time before it is noticed. I have seen massive amounts of mold on the back of drywall that was slightly moist for a long period of time and there was nothing on the other side of the wall to hint at the issue.

Things to consider in their place would be solid wood, magnesium oxide, and perhaps stone or tile.


Carpets love to grow mold on the backing. You also get mold in the carpet pile. You can't get it all out and when you clean it, you get it wet and may actually add to the mold issue if you don't get it completely dry within 24-48 hours. If you have someone come into your house or business to clean carpets, and they bring their own equipment to your residence/business, they can also bring mold or bacteria from other cleaning jobs to inoculate your space. Carpets are a great place to grow and harbor mold. I suggest ripping out all wall to wall carpeting.

Wood floors are my choice in the house I live in. The only issue with them is if you get wood that is contaminated when it goes in or if you use a high VOC coating to finish it. There are low VOC products on the market today. I really like wood floors. To me they are the best of the choices out there. Just remember all wood needs to be finished or any moisture that gets on it will easily grow mold. All natural surfaces such as wood grow mold easily if moisture gets on the area for more than 48 hours. I mop wood floors very infrequently and usually do spot mopping in between. This keeps moisture away from the wood. Technically, the finish will protect it, but I am simply super careful since I am a mold susceptible person.

Radiant Heating in Flooring

If you have radiant heat in your flooring and you think there is a leak in your house, this is a a place to look and it is a hard one to find and deal with. Radiant Heating in Flooring feels great, but what will you do if you have a break in the radiant heating system. Are they built in such a manner that your house will be protected from the liquid and will you have easy access to the pipes to fix them?


Most insulation currently in houses holds onto moisture and supports mold growth. Luckily this has been recognized as an issue but not enough is being done about it. Rockwool or aircrete-type-insulation might be your best choice. I have seen houses where the insulation was put on backwards and which creates an even bigger mold issue.

Damp spray insulation may be a problem. If you use it, make sure you leave your walls open (no drywall) until the cellulose has properly dried. Finally, you can only damp spray cellulose into open wall cavities where the studs are exposed. Never pump cellulose into closed wall cavities. If you do, you almost certainly will have a moisture problem. (For that application, you would use dense pack (dry cellulose).


Wall paper

Oh my, are we trying to feed the mold. The mold loves to grow on that nice glue and the paper. You can create a really great mold environment by wall-papering your house. Some of the wall papers have surfaces that are impermeable. They are even more likely to collect moisture behind them that can't get out.

Heat Sources

Ductless HVAC

The nice thing about these units is that you do not have the duct work. They do however grow mold at times and need to be watched carefully.



It is easy to get mold growing in an HVAC system. The main area to have inspected more often than others is the evaporator coil.

An HVAC system found to be contaminated with mold should be turned off and not used until the system has been remediated. Using a mold-contaminated HVAC system may spread mold throughout the building. If the HVAC duct work is metal, it may be remediated in a manner that will work for the person living in the home. However, if it is a porous material, I suggest you throw the duct work out and put a cleanable, metal duct work in its place.

Mold growing near the intake to an HVAC system indicates potential ventilation humidity problems. An HVAC system that is part of an identified moisture problem may also be a site of mold growth. Experience and professional judgment should be used when working with the HVAC system; consult a professional if needed.

The HVAC system has the potential to spread mold throughout a building. Known or suspected mold growth in HVAC ducts or other system components should be investigated and resolved promptly. If mold can be seen growing on the inside of hard surface ducts (e.g., ducts made of sheet metal), consider cleaning the ducts. There is an EPA guide Should You Have the Air Ducts in Your Home Cleaned?

If the HVAC system has insulation on the inside of the air ducts , and the insulation gets wet or moldy, it should be removed and replaced because the material cannot be cleaned effectively. (Personally, insulation inside an air duct that can get moist just seems silly. I would not buy such ductwork.) Please note that there are no antimicrobial products or biocides approved by EPA for use on lined ductwork.

Mold should be removed physically from the HVAC system but some people find using ozone or other products pushed through the HVAC system can be helpful for lingering smells. Be aware that some products can damage the system and many of them may not be  compatible with the warranty of the HVAC system. Ozone can also cause damage to your lungs.

Wood Stove

I am giving a plug to wood stoves here as they decrease moisture in the house. They have their own issues, but if you are well acquainted with the proper use of a wood stove this is a great method of heating. If you are one of those people who tend to want to tamp down your wood stove so you keep it going all night,  or all day while you are at work, please realize you are poisoning all your neighbors with the crap coming out of the  chimney. (It's okay, I realize you did not know.)

Keeping the moisutre down with a wood stove does not keep all mold from growing. Although moisture is the number one issue to keep in mind for growing mold, there are some molds such as Wallemia that can grow in low moisture environments. So, keep the moisture under control, but realize you can still get a mold issues in lower moisture environments, it is just not as likely.

Mold is Visible

Oh my, this is really bad. Remediate immediately. Remove the materials with mold on them unless it is non-porous or superficial and the mold can completely be cleaned up as well as the smell. Be aware that dead mold can still cause allergic reactions and other health effects in some individuals, so it is not enough to simply kill the mold. It must also be removed. Clean anything in the moldy area with either hydrogen peroxide or quaternary ammonium compounds in case there are bits of mold or spores or mycotoxins you can not see. All surfaces need to be cleaned. In some cases hydrogen peroxide will damage the building materials and the quaternary ammonium compounds are best to use. This needs to be done in a methodical manner so as not to move the spores around the room. Unless is is just a little tiny amount of mold, the area needs to be contained and unless you know how to contain the area and clean it appropriately, it is best to hire a professional. See the data on cleaning  tips for a moldy home.


Additional Information That Is Useful

If you feel you are living or working or being educated in a moldy building, you can get information on testing here.

You can get information on cleaning up a moldy building here.

I suggest you read the World Health Organizations Indoor Air Quality Report of 2009. You can download it here.

I would also suggest you read the "Indoor Environmental Professionals Panel of Surviving Mold Consensus Statement" on "Medically sound investigation and remediation of water-damaged Buildings in cases of CIRS-WDB."

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