Where to Sample

Contact information: May Dooley,  888-735-9649, may@createyourhealthyhome.com – Mail to: 1009 Hemlock Circle, Manheim, PA 17545

In this tab, I tell you where to sample, using my own experience at homes.  In an average house, I’ll take 20-40 tape samples, 5-15 in the average apartment. They typically tell me more about where mold is growing – and where it isn’t growing – than the air samples do. I take air samples for a back-up, but to me, the tape samples usually are more important.

On the other hand, sometimes air sampling reveals mold contamination that tape samples miss. A tape sample is at best a spot-check. The reverse can also be true, that tape samples can pick up contamination that air samples miss. If I had to choose between tape and air samples, I’d choose tape samples. Even if I only had air samples to work with, the results still wouldn’t tell me what surfaces mold is growing on.

Tip:  The gravity plates air sample Petri dishes (test kits) available in home supply stores are not known for their accuracy. There are 3 big issues with them: 1. Getting an under-count and having a false sense of security; 2. Thinking that the common black molds are “the” black mold and getting upset over nothing; 3. Thinking that 1 or 2 green colonies (Penicillium and/or Aspergillus) mean the house is contaminated – when a few colonies could grow in any house. 

If there is suspicion of mold in an area, I often sample both discolored and clean areas (two separate tapes). It can be helpful to know if invisible mold is growing on the clean-appearing surfaces or if mold seems to be confined to discolored areas. The answer to that question can have large implications for how much clean up is involved.

Disclaimer: This section is not all inclusive for where to sample for mold. There are often surprises at homes, so I will attempt to give you tools for detective work. If you find an example that might be useful in this section, please send me an email. My best classrooms have been the homes of my clients.

First and foremost as we figure out where to sample:

I include my clients on my inspection. They provide many clues as to where mold might be. They give me the “grand tour” before I begin. I ask them the history of roof and plumbing leaks. I ask if the house has drywall or plaster walls.  (Mold doesn’t like plaster but loves the paper backing of drywall.) I ask them about water intrusion in the basement or crawlspace and about where they might smell musty odors. I ask if they run a dehumidifier in the summer. I make note of below-grade finished spaces (like finished basements, the lower level of bi-level houses, and lower rooms in split-level houses).

I ask about the AC system. When was it installed? Do they use it a lot? Was it ever cleaned? When? Did they notice feeling better after it was cleaned? What kind of filter is used? (pleated filters are best)

I also ask about symptoms. Does someone in the house have symptoms (such as respiratory, headaches, etc.)? Do they feel better when away from the house or away from the area? For example, two clients had their sinus conditions greatly improve after moving from a mountain valley to the plains of Georgia.

I ask about past remediation (treatment for mold) and renovations/ additions. The homeowners are my greatest resource for getting clues on what might be significant.

Once a teacher….

I not only ask my clients for a tour of the house and a verbal history of water incidents and symptoms, but I like to include them in the inspection (when they are willing or able). They learn more, we can cover more ground in less time, and it’s a nicer day for all of us. How might that work?

Take my last inspection. “Hal,” the husband, was volunteered to do the air samples, so I got him set up to do the culture plate sampling in every room, each AC zone, the room air purifier, an outside sample. He worked hard, but it still took him close to 2 hours. Each sample took 2 minutes, so in the 2-minute wait time, he worked with a moisture meter, checking around plumbing, in sink cabinets, around toilets and showers, and under windows. He didn’t find any leaks, but if he had, I would have known to do extra sampling in that area (tape samples under base molding or perhaps a drill hole in the wall for tape and/or culture plate air samples).

Tip: I prefer culture plate air sampling to spore trap samples for diagnostic purposes. I can see the types of mold that grow and better pinpoint sources. With spore trap sampling, the spherical spores are lumped together. I don’t know whether the predominant molds are Aspergillus, Penicillium, Trichoderma, Mucor, or other molds with spherical spores. With culture plate sampling, I can also incubate the mold plates in my garage and study them in-house, so there are no lab fees involved. We can afford to do the 15-25 samples, because the homeowner provided the labor, there are no lab fees, and they only pay for an hour of my time a week later to study the samples. It’s a win-win situation. If a paper trail is required for legal purposes, or if time is of the essence in a real estate transaction, then I’ll run the spore trap samples and send them to a lab.

While Hal was off doing his job taking culture plate air samples and checking with a moisture meter, Sharlet, the wife, and I measured the electromagnetics, especially at two bedrooms where folk didn’t sleep so well and had Lyme disease. We learned that AC magnetic fields were low (no power line issues), that DC (direct current) radiofrequency was low from the outside but that an innerspring mattress was serving as an antenna for those fields, that in one bedroom WIFI fields from 2 stories below were elevated (recommendation: switch to cable or turn the router off at night), and that body voltage readings were high but could be reduced (from 14,000 mV at one bed to 18 mV). Instructions for measuring and reducing voltage at beds are found in the EMF section of this website. Many people sleep better when this is done.

We also learn that some of the electrical outlets were miswired and that the master bedroom addition may have a wiring error. I referred them to a consulting electrician/electrical engineer as a back-up to their electrician.

We next went to the basement office where the router was located. The WIFI radiofrequency fields were much higher there, throughout the office. I compared those readings with the reading in my office, where I had cable instead of wireless. The Acoustimeter readings were at the lowest level in my office, and at much higher levels in their office.

Another area that typically is high is the base station of portable phones. Folk don’t realize the radio frequency radiation associated with these phones, and also with cell phones. Use a land-line for extended conversations. I wouldn’t want portable phones in my house.

After we finished with the EMFs, then Sharlot and I started with the mold part of the inspection. I showed her what mold looks like under the microscope and photos I had taken at another house. Then we commenced to take tape samples, starting with the basement room where she had the most concern. She walked around with me as I explained the rationale for what I was testing and showed her how to do tape-sampling.

I put the tape samples from that basement room under the microscope, and we got immediate answers about whether there was mold or now and how much. The room didn’t have much mold at all, to Sharlot’s relief. She understood that sometimes air sampling revealed issues that didn’t show up in the tape spot-checks and appreciated that we were doing both, surface-sampling and air sampling.

She was next concerned with her daughter’s bedroom, so we went upstairs and took about 10 samples in the bedroom – anything that we could think of that might be suspect…the base of molding on exterior walls, the lower perimeter of a closet, clothes in a closet, the underside of box springs, slats under the box springs, peeling paint on a wall, dust on the top of an overhead fan, backs and bottoms of furniture. Some of the samples were composite samples, where, for example, we sampled 6-10 spots on all the furniture in one tape. Going downstairs, we reviewed these tapes – nothing. We found no mold at all.

Then we finished the rest of the house, from attic to basement/ crawlspace. Sharlot started to work with the microscope, with me checking her work and making suggestions. She discovered the mother lode of mold in the 2F hall bathroom sink cabinet. There were high levels of Aspergillus around the plumbing. They had been planning to get rid of that cabinet, anyway, so we talked about safe ways of removing and discarding it to avoid spreading mold particulates hither and yon.

After mold, we did the shorter inquires – checking for gas leaks, checking the vacuum cleaner to see if was HEPA-quality, and checking for lead paint. There were no gas leaks, the vacuum cleaner wasn’t bad but not the best, and there was lead paint on base molding and the exterior of the house.

If I had only 8 samples to take (the $50 option), here is where I would sample:

  • Inside bathroom and kitchen sink cabinets – because that’s where the plumbing is (sample where the back wall meets the base);
  • Basement or crawlspace ceiling joists/subflooring, several spots;
  • Under lower wood steps of basement stairs;
  • If house is damp, a spot-check of undersides of furniture;
  • A spot-check of contents stored in basement;
  • Areas with suspicious discolorations or known past leaks
Now, let’s you and I get to work!

Where to sample, that’s the question? Where do we start? Here, we’ll start at the top of the house, in the attic and work our way down. Come along with me on an inspection.

Attic – where to sample

What I’m asking myself:

  • What is the attic ventilation like? The more modern view is to have a ridge vent and soffit vents (between the roof and the sides of the house) rather than screened vents at the ends of the roof. Either can work, but there should be something for ventilation. Roof or side exhaust fans can be good, too. Sometimes insulation is mistakenly extended over the soffit vents, closing them off. If I’m inspecting in warmer weather, a really hot attic could be a sign of poor air exchange.
  • Is ventilation poor, so that moisture from below could get trapped in the attic? Where do the vent pipes from the bathrooms terminate? Are the pipes dumping moisture into the attic? Is the moisture then trapped in the attic? I’ll look for green or white fuzz where the rafters meet the sheathing (roof decking). I’ll also check the sheathing around where the pipes dump the moisture, assuming it’s accessible. I don’t attempt to walk in attics where there’s no floor.
  • Is sheathing on the north side of the attic (being cooler) more discolored than the south side? Temperature gradients can result in condensation.
  • What is ventilation like in the attic? If I’m inspecting in the summer, is the attic really hot? That would be a sign of poor air exchange.
  • If there is an AC unit in the attic, was there leakage at the drain pan? Is there water staining or mold on the plywood around the pan?
  • Are there dark splotches on rafters? This could be a sign of Chaetomium mold that came in at the time of construction.
  • What the history of the roof? How old is it? How many layers? On an average, the economic lifespan of an asphalt shingle roof is about 20 years. Aspergillus/Penicillium growth can result from a neglected, leaking roof.

What I look for in the attic:

  • Dark sheen on the sheathing (support layer for roof) – which could be a sign of condensation, an exhaust vent that terminates in the attic, and inadequate ventilation. This mold might be Cladosporium, Ulocladium, or some other common mold. The condition might be worse on the north sheathing than the south.
  • Black splotches on rafters – usually left over from the time of construction. This mold might be Chaetomium, usually dead, with spores long gone. It usually looks worse than it is, but it also should be dealt with, because a home inspector could point it out at time of re-sale. An easy way to deal with it is to spray Concrobium’s mold stain remover on it. Always wear a respirator when working with mold. A P100 or N95 respirator can be bought at a home supply store. Get one with a nostril valve for a little easier breathing.Tip: Some folk with heart, lung, or other related conditions, should not wear respirators. Check with your physician if you have a question.
  • Green or white fuzz where rafters meet the sheathing. This mold would typically be Aspergillus or Penicillium and would result from moisture being trapped in the attic. Sometimes insulation covers the soffit vents.
  • Areas of water-staining from roof or flashing leaks. This mold could be Aspergillus or Penicillium, Cladosporium, etc. Sometimes water runs down a chimney due to a chimney flashing leak. If drywall is present, the drywall could have Stachybotrys growing on it. You can’t randomly cut into the wall below the chimney, but you can use a good flashlight to look down into the wall cavity from around the chimney.

Where I sample:

  • If I see no discolorations, I do a composite sample on a half dozen spots of wood, often from the entry area – including sheathing, rafters, support lumber, etc. Mold can be present that is not visible to the naked eye.
  • If I see discolorations that are accessible, I’ll touch the tape to the discolorations. If mold is present, there should be discoloration now on the tape. If the tape remains perfectly clean, the discoloration may be just a stain on the wood.
  • I take a dust sample from a metal or plastic surface. This gives me an idea of how many spores – and what type – are floating around in the air. If there are a lot of Aspergillus/Penicillium-like spores (spherical), I would suspect leakage and contamination.

I make sense of the data:

  • After the tape samples are studied, I sort out the findings and try to figure out the scenario that would account for the data. My recommendations flow out of this exercise. I may recommend things like improving ventilation, uncovering soffit vents, putting in a ridge vent when re-roofing, adding an attic fan, mold remediation, replacement of insulation, and removing mold stains with the Concrobium product.
  • Since there is a big concern with climate change, I also recommend having an energy rating done. A good part of escaping heat from below escapes upwards through the attic. If your attic hatch doesn’t have adequate insulation over it, it serves as a chimney for heat just pouring upwards. Why not find out where the holes are where heat is escaping and get them sealed off? You’ll pay a one-time cost for savings ever after. You ARE going to spend the money. The question is whether you’ll invest in lower energy bills in the future or keep paying for the escaping heat year after year after year. Whose pocket will the $ go into?
Living areas – where to sample

Let’s move down to the living areas now.

What I’m asking myself:

  • Is mold present in sink cabinets and near plumbing? Is there risk that the water penetrated below the base of the cabinet? If so, the bottom may need to be removed and the cavity below cleaned out and surfaces encapsulated, or the cabinet replaced.
  • Is there an access hole to the bathtub fixtures?
  • Were there any past plumbing or roof leaks or ice dams that might have resulted in hidden mold in wall or ceiling cavities? Should a test hole be made in a wall or ceiling? (Many mold particulates could be released to room air if a hole is opened, so take precautions accordingly.) We’ll talk more about that in another tab.
  • Do I smell mold anywhere? If so, there is growth in the vicinity. This may be a sign of a damp house. Does the land slope toward the house? Are downspouts terminating right at the foundation? Are gutters kept clean? Is there a lot of vegetation around the house?


  • I seldom sample on base molding (unless there is visible water-staining), but I’ll often sample on the underside of base molding if I can access it. If there is mold in this area, it typically would be hidden in the wall cavity.
  • Sometimes with a ranch on a slab and land sloping toward a wall, there can be wicking of moisture up into the wall cavity. I’d check with a moisture meter, do a tape-test under base molding if accessible, or possibly drill a hole in the wall for air sampling or tape sampling.
  • I seldom sample on painted or finished surfaces. I go for the rough, unfinished surfaces, because it is easier for mold to get a foothold on rough surfaces. Sometimes, of course, the environment is so damp that mold is growing on finished surfaces, too. Usually that mold is visible to the naked eye.
  • I seldom sample just one surface with one piece of tape (unless I see what looks like mold and I just want to find out what kind). I’m touching my tape firmly to a half dozen similar surfaces to expand my data base.
  • I try to have in mind what I’m looking for. I don’t sample randomly. I’m trying to think like mold – where would it find food and water? Think about why mold might grow where you’re thinking about sampling. If you can’t come up with a good reason, it might not be worth testing that spot in living areas.

What I look for in living areas

  • Water-staining on walls and ceilings, in closets
  • In sink cabinets around plumbing
  • On furniture, if damp environment
  • On flooring around radiator valves

Where I sample in living areas

  • Discolored areas on bathroom ceilings
  • Inside bathroom and kitchen sink cabinets, especially at back crack where the back wall meets the base – and at plumbing access holes if I can get a finger with tape around it in thereTip: Laminated sink cabinets (and cabinets that have waterproof shelf liners) usually aren’t an issue, though water could penetrate below into the cavity below the base. Still check at the crack where the base meets the back wall.
  • If grout has not been maintained at a bathtub, there is risk for water penetrating into the wall cavity, promoting mold growth, including Stachybotrys. Some removal of building materials may be needed to find this mold.
  • In a damp house, on the underside of kitchen cabinets and under base molding in a closet or two.
  • In a damp house, on furniture (unfinished bottoms and backs, on upholstery, on the underside of box springs)
  • Antiques or items bought in a garage sale
  • Plant tables and floor area, if plants have been over-watered
  • Under bottom of base molding – Without making a hole in the wall, sometimes you can get a clue whether mold might be present behind the wall by testing at the base of the wall, under base molding. Put tape over the end of a blunt kitchen knife, and slide the knife into the crack between the bottom of the molding and the floor. Touch a few spots at the bottom of the molding.
  • Under bottom of base molding at common wall with shower fixtures (ex., if the shower fixture wall backs the bedroom closet, I would test from inside the closet, under base molding). If the shower fixture is on an exterior wall, there’s nothing you can do, except check with a moisture meter if you have one.
  • Take off a vent cover and sample inside the vent. Try not to get too much debris on the tape. You might sample on the sides of the duct instead of the bottom, if there’s a lot of debris on the bottom. Occasionally I find the tape is solid with black Cladosporium inside the duct, but not often. There could also be elevated levels of Aspergillus/Penicillium-like spores.
  • If there is a Select Comfort mattress bought before 1994, I would test next to the membrane for discoloration, which may be Cladosporium. The company reportedly resolved this mold issue in 1994.
  • If someone is ill, I would pay extra attention to their bedroom. I might do a composite sample, i.e., touch one tape to many surfaces to rule out mold. If mold shows up on the tape, then I have to go back and do tape samples for each item in the composite sample, until I find out where the mold growth is.
  • I don’t usually test painted surfaces, because paint contains mildewcides, which typically protect it from mold growth. If the wall got wet and remained wet, all bets are off, and mold could grow, but you’d probably see that mold. (Mildew, by the way, is mold. Fungus is mold. Same thing.)
  • AC diffusers (vent covers) – If black mold is present here, it typically is Cladosporium, which likes areas of condensation. Just wipe off the Cladosporium. This doesn’t automatically mean that the system is contaminated.
  • If a house has newer stucco, there may be risk for hidden mold if the stucco was not properly installed. There are inspectors who are certified to inspect the newer stucco. 

I make sense of the data

  • What mold remediation scenarios are present here? Is remediation needed in a sink cabinet because of a plumbing leak?
  • Is remediation needed at a ceiling or wall drywall cavity because of a plumbing or roof/flashing leak or because of other water intrusion from the outside?
  • Is remediation needed throughout the house because of a dampness condition? Is furniture, etc., salvageable?
  • Is there an issue with the HVAC (heating, ventilation, and air conditioning) system? Is cleaning needed? See the remediation tab for more information.Now let’s continue downstairs to the basement.
Basement/Crawlspace – where to sample

What I’m asking myself

  • Is mold growing on structural items (ceiling joists and subflooring)?
  • Is mold growing on contents (stored items and furnishings)?
  • Is mold growing behind finished walls?
  • Is mold growing on the underside of steps, especially lower steps where it is damper?
  • Is mold growing on other unfinished wood surfaces, such as work benches and the wood backing of the electric box?


  • Mold grows on softer organic surfaces faster than on shiny or finished surfaces. For example, mold would grow on dull wicker faster than shiny wicker and on upholstery and unfinished wood faster than on finished furniture surfaces.
  • Mold doesn’t usually grow on concrete, but if there are efflorescence (mineral deposits) and organic matter on the foundation walls, it could grow on the organic matter. Mold here is a maintenance issue. Vacuum and wipe off with vinegar or Borax solution. See what you can do outside to reduce water intrusion at these areas. Using a dehumidifier may increase the rate of moisture coming through the foundation wall – but you may have no choice if you have a finished basement, unless you live in the desert.Tip: If your basement or crawlspace is made of cinder blocks, use of a dehumidifier can cause deterioration, from the outside in. Water is pulled through the cinder blocks. Lime, the glue that hold the concrete together, is water-soluble. As lime is removed, the concrete degrades. There may be alternatives to using a dehumidifier, such as:
    • Encapsulate vulnerable materials and don’t serve lunch to mold. Then set up a fan catty-corner to ricochet air around the basement/crawlspace.
    • Use a dehumidifier just during very humid weather.
    • Look into www.theWave.com. I don’t have experience with this unit, but several clients have told me it’s worked better than a dehumidifier for them, for almost no increase in the electric bill. That’s a strong contrast to the amount of energy used by a dehumidifier.Tip: If you do purchase a dehumidifier, get an EnergyStar one and one that you can take apart and clean. They tend to get moldy.
  • New wood is more vulnerable to mold than old wood. There may be much less mold in the basement of a 90-year-old house than in a 2-year-old house. That’s a surprise to many people.
  • If your house is old and you see whitish paint on ceiling joists and subflooring, that’s probably old whitewash. Whitewash is still being used around the world against mold and insects. You can make your own whitewash – go on-line for a recipe.
  • If contractors would encapsulate all wood in the basement at the time of construction, they’d eliminate the need for many future mold remediation projects.
  • Finishing a basement can be like serving lunch to mold. It may not be the original structure that’s the issue, but what we bring into the basement that results in mold growth.
  • Basement foundations aren’t waterproof typically. Thus, if drywall is put up near a foundation wall, moisture migrates through the wall and can cause mold growth on the paper backing of the drywall.

What I look for

  • If I could take only 4 tape samples in a basement, here is where I’d sample:
    • one tape of dust on a metal or plastic surface
    • one tape for a composite sample of subflooring and ceiling joists
    • one tape for the underside of wood at lower steps
    • one tape for vulnerable contents (bottoms/backs of furniture, upholstered surfaces)
    • one tape of dust on a metal or plastic surfaceThe first sample would help me gauge the number of spores floating in the air. From this, I could make a recommendation about whether a respirator should be used when in the basement. This gives me a jump on the air samples, which will take 5-6 days to develop.The next 3 samples would help me gauge the amount of mold growth on structural elements (subflooring and ceiling joists) and on contents. The underside of lower steps is a marker area for Aspergillus. If levels are high there, I know the basement is at elevated risk for mold and that I can expect mold growth on stored items.Additional testing is just filling in the blanks, determining the salvagability of contents, figuring out an approach to remediation and cleaning, determining if the homeowners should wear respirators in the basement, seal off the basement temporarily, etc. I would also try to get a sense of whether a remediation job calls for a professional team or could be done by handy homeowners or their contractors.

Where I sample

  • Furniture, especially unfinished wood surfaces and upholstered surfaces
  • Ceiling joists and subflooring (supports the 1st floor) – I’ll test in about 3 sections of the basement. Sometimes I check the ceiling joists and subflooring in separate composite samples, sometimes together. It doesn’t matter that much, since if mold is on one, the whole ceiling will be addressed.
  • Underside of steps, near floor
  • Behind a finished wall near floor – try to access from an unfinished room, such as a utility room. Sample the back of drywall, the sill plate, lower part of studs, insulation.
  • Behind a finished wall near floor – Try to access below base molding by placing sticky tape over a blunt knife and then sliding it underneath the base molding.
  • Insulation in ceiling – surface of fiberglass covering & fiberglassTip: In my experience, insulation between ceiling joists typically protects the surface area it covers from significant mold growth, leaving just the exposed edges of the ceiling joists vulnerable to mold. Insulation must be installed at the time of construction, before mold gets a foothold.
  • On surface of paneling, especially in cracks
  • Sill plates (horizontal lumber on floor, base of studs)
  • Carpet (Tapes are not the best way to sample carpet; lab testing of vacuumed dust is better.)
  • Surface of air filter
  • Inside ductwork, if accessible. AC coils, if accessible. This may be a job for your AC contractor, unless you are handy and know what you are doing in getting to the coils.
  • Dust from plastic or metal surface – to gauge how many mold spores may be in air
  • Foundation wall, discolored areas by floor

I make sense of the data

  • Is mold an issue at structural elements (ceiling joists and subflooring)? Recommendations? See another tab on Remediation.
  • Is mold an issue with contents? Recommendations?
  • Do steps need to be taken to reduce water intrusion from the outside?

Well, now you may know more than a lot of mold inspectors. It’s time to put your knowledge to the test and take some tape samples. After you get your mold questions answered, it will be time to learn about remediation options.

When you are ready, meet me at the How to Remediate tab where we’ll discuss what to do, once you know you have mold and where it is.





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