Have You Seen What’s Hiding Behind That…
…drywall, flooring, ceiling, baseboard, et cetera? Children often fear the unknown monsters hiding beneath their bed or in the closet, but it’s the adults who should be afraid. The monsters hiding from them are real. I’ve seen a bunch of nasty stuff hidden from view in the many houses I’ve inspected, worked on, and lived in. So in case you need a reminder, here’s a sampling of some of the uninvited stuff—living, dead, or inanimate—that may be hiding in your house.
Dead critters
I’ve found three dead rat skeletons in my basement. You can see two of them above and below and the other in this article. One was caught in a rattrap on top of the dropped ceiling; the two shown here died inside walls.
I had an interesting—read terrifying—encounter with a dead possum in a crawl space one time. I was squeezing through a tight spot to get to a duct I needed to repair when I saw grey fur. I scooted backward as quickly as I could and then noticed there was no movement. “Ah, it’s just playing dead,” I thought. No, it really was dead. But I was happier to deal with the odor when we removed it rather than having my nose bitten off by a live possum.
Live critters
From ants to raccoons, live animals love finding cozy spots to hang out in your home. Sometimes they stay till they die (see above). Sometimes they’re transient guests (see below). And then there are the ones still living with you, whether you’re aware of them or not.
The photo above shows camel crickets in a crawl space. There are seven in the photo, plus all the spots they’ve left on their wooden toilet. I’ve seen live snakes (only harmless ones so far), mice, birds, bats, feral cats, and more.
The one that scared me the most was a flying squirrel. I was pressing fiberglass batt insulation down into ceiling joist cavities when one popped up and almost hit me in the face before scurrying to to the soffit to escape.
Long-gone critters
Sometimes you see only the evidence of past visits or occupancy of animals. Below you can see the remains of a giant wasp nest inside the wall of Aubrey Gewehr’s house in Portsmouth, New Hampshire. They carved a hole in the blown fiberglass insulation to build their nest.
![An abandoned wasp or hornet nest inside an exterior wall in New Hampshire [photo by Aubrey Gewehr]](https://www.energyvanguard.com/wp-content/uploads/2025/12/wasp-hornet-nest-in-wall-aubrey-gewehr-1000.jpg)
Microbial growth
Microbes of various sorts, including many kinds of mold, love a house with damp conditions. The photo below shows the back side of some wood paneling I removed from my basement. I wonder how many different species of microbes colonized that wood.
And you may have seen that paneling before. In the spring of 2020 I began writing my book, A House Needs to Breathe…Or Does It? I used the photo below in one of my updates to those who had pre-ordered the book. At the time, I had no idea how bad the other side of that paneling looked.
Termite damage
Surprisingly, I found little termite damage when I remodeled my basement last year. I did find some, but it was just behind the bathtub on the exterior wall. The photo below shows another house where the baseboard in the basement had been eaten by termites. And they also made a little mud tunnel in the corner to go up the wall.
Holes
Oh, the many holes you see when you look beneath the surfaces! Some are there for obvious reasons, like the hole where a duct passed through a concrete block. The reasons for some will always remain a mystery.
And then there are the what-the-heck-were-they-thinking holes. You may have seen this one before, but it’s an absolute classic. The photo below shows what I believe to be a refrigerator vent. It was a huge hole in the kitchen ceiling right above the back of the fridge.
Of course, there are also the crawl space vents open to the space above dropped ceilings in conditioned basements. That one’s pretty common in the Atlanta area…and it provides a great opportunity to make a big improvement in your home’s airtightness. The photo below shows one I found in my house during the basement remodel last year. (You can read more about it here, where you also can see the “after” photo.)
Rot
Uncontrolled moisture and wood are a recipe for rot (and termites and microbial growth). I think you know what it looks like already, so one nice photo should suffice.
Toxic and hazardous materials
Asbestos is one of the most common hazardous materials found in older houses. It could be in vermiculite insulation, floor tiles, the black mastic used as adhesive for floor tiles, and drywall joint compound.
The place I’ve seen it the most, though, is in the white cloth tape on HVAC ducts. The photo below shows what it looks like. The problem here is that it has a higher asbestos content than some of the other materials, and it starts falling apart as it ages. When we had the asbestos abatement done at the beginning of our basement remodel, I asked the inspector how often that tape tests positive for asbestos. His answer: 99 percent of the time.
The asbestos in drywall joint compound, floor tiles, and black mastic is generally safer—but NOT safe—because of the lower concentration and because it’s less friable than the the asbestos duct tape above. Still, it’s best to encapsulate it with something like PerfectPaint or PerfectPrimer.
Structural problems
Then there’s a whole other kind of scary. I found what you see below in my basement. That’s a steel I-beam being supported by a steel pole. Unfortunately, the beam is resting on only about a half-inch of the pole. Yikes! If this house were in California, it may not have lasted this long because the only other support for that beam is about 18 feet away at the other end of the beam. Double yikes!
The stuff left behind
And then there’s the stuff that workers leave behind. Sometimes it’s accidental. I’ve picked up a few perfectly good tools from contractors who forgot them.
Sometimes it’s intentional. I’ve found all kinds of trash but also some more interesting stuff. That empty whiskey bottle was inside one of my foundation walls. I’ve found beer cans in attics, too. The worst one I’ve heard about was an open cup of urine inside a garage wall. The owners of the house had to tear open the wall to find out what was making that awful smell.
Well, there you have a little glimpse behind the curtains…or drywall, wood paneling, insulation, or whatever is covering those secrets that may be hiding in your home. Now, what are you going to do about it?
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
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A dead squirrel, leathered, in the return duct!
Live snake on the sill plate. (granted, is was a very tiny garter, not like the giant skin you found!)
And,
The ever-anticipated empty beer can! While not hazardous, it explains a LOT about failed or poor construction. Ever wonder why walls aren’t quite so plumb? lol.
scott: You just reminded me about the section I meant to include about stuff left behind. It’s now there at the bottom of the article, with a photo of a whiskey bottle I found in a CMU wall in my house.
A mouse, still damp and slightly liquified, in a wall cavity that emanated the odor of chocolate into the room for over 3 weeks before we figured out the location of the odor! Yep. Both the owner and I agreed – chocolate. Still don’t know what chemical it was giving off. But was more like Hershey’s than Nestle’s! lol.
Eww! Could be butyric (butanoic) acid from the mouse’s body fats going rancid?
Adam Ragusea did an interesting video on why Hershey’s tastes like vomit; see also:
https://www.whitakerschocolates.com/blogs/blog/why-does-american-chocolate-taste-bad
Chris I LOVE this… rancid body fats makes sense.
I relate to strange odors – vomit has that odd “acidic” nature, I often smell “skunk” from the unlikeliest sources – many herbs and flowers have similar base odors, basil, lavender, oregano, have skunk undertones…. some stronger than others. These ALL smell like weed – both raw and smoked! lol…. and I am nauseated by all of them…
Chocolate on the other hand, well that odor of the still-wet dead mouse was actually “good”… I wanted to go get candy when I left!
Great post Allison – these are just some of the troubles you see in vapor open wall cavities and vented crawl spaces. Most builders will never change, so I think it’s up to a new generation of builders to build in better ways. We have hope for a better tomorrow.
Thanks, Charles. We have a lot of work to do, but like you, I’m hopeful.
“Now, what are you going to do about it?”
100% new construction. The days of gut remodeling existing houses are behind me forever. Sweat equity is greatly overrated.
John: Yeah, there’s a reason that remodelers always include language about additional charges for unknowns in their contracts. New construction is usually easier…unless you find out there’s a giant boulder just beneath the site or something like that.
I have renovated two old houses over the years. The current one is an 1890 prairie victorian farm house.I came across many skeletons of various animals (mice, rats, bats),along with their very large nests as well as a few collectables of very old photo’s, playing cards and even a Dakota County School (Minnesota)report card from 1880. Your article was so much fun to read, as anyone that delves into the unique and challenging world of renovation (especially old homes and buildings) should know that it can be as much a treasure hunt as it is dirty work. Thanks for the article and Happy Holidays everyone.
Jeff: I’ve also found an old baseball card for a 1960s Houston Astros player. I didn’t recognize the name, and it wasn’t worth anything when I looked it up. That 1880 report card sounds interesting.
Great article Allison! We actually had a client ask us to insulate an attic in a rental house. When we did the visit to the property for the estimate we noticed several dead flying squirrels. We recommend to the client that we remove the insulation and disinfect, but the client did not want to do a removal… only blow over the existing nasty stuff in attic. We decided that the reputation of our company was more important and we walked away from the work. Oh btw, the tenant was complaining about a strange smell and being sick.
Ryan: You did the right thing. Sometimes it’s best to just walk away.
Speaking of treasure hunt… In one house, two glass (formerly mayonnaise) jars both filled with quarters were found buried under the insulation the attic… $1,500 if I recall. In another house, one from what used to be a pair of diamond earrings was found in a floor supply branch duct. And of course… the countless collections of loose change in the ducts. It’s not all bad news! Wishing you a happy find at your house through the holidays.
Rick: Wow! I’ve never found money…well, maybe a few small coins worth only their face value. I guess tools have been my most valuable finds.
I had a friend who found an empty 5-gallon joint compound bucket in the basement that someone took a dump in.
Roy: Oof! At least they didn’t leave it behind the drywall.
I just added another section that I’d meant to include from the beginning. It’s the second-to-last one and is titled “Structural problems.”
My favorite find was a Confederate paper money note in a home I once owned in Charleston SC–older than the house. Allison–you know my solution eliminates the critter problems: solid walls of autoclaved aerated concrete, wrapped in mineral wool board insulation, directly applied hydrophobic, permeable, insulating stucco, and passive house doors and windows. No air leaks, no bugs. The easiest passive house imaginable–AAC is airtight. The norm in much of the world since it was developed in Sweden in 1923. China is now the world leader in production in part because of AAC’s environmental attributes (add that to electric vehicles, batteries, and photovoltaic panels).
Daniel, I am familiar with aerated concrete, but you add the term autoclaved (what I think of as heating for sterilization)… This I’ve never heard. Can you give me the short version explanation of what that does for the material? thanks!
Scott, The inventor tired of waiting for masonry samples to dry, so he put them in a laboratory autoclave–that is what you are thinking of. A trace of aluminum reacts with the alkaline ingredients in a mortar mix to give off hydrogen, which acts as an expansion agent. The heat and pressure changed the crystalline structure, strengthening it. The autoclaves grew to handle multiple AAC ‘cakes’ 2′ x4′ x 20′. A general search for “autoclaved aerated concrete” will bring extensive information, or “AAC Passive House” will lead to what a colleague and I have been doing; we met after discovering we were both using a product not well known in the US yet ideal for passive buildings. There are now thousands of manufacturing sites worldwide, but only 2 in the US. “Bellwether on Main” in Hillsdale is now on AirBnB and Vrbo as a teaching tool to improve US housing stock.
Daniel – excellent explanation – ez to follow and understand – “makes sense”. Chemistry at its finest!
So using AAC means paying for long distance shipping in nearly all places.
thanks… if you have any favorite sites, links, etc please share – you can send them off group to he**********@*ol.com….
Scott, Not to overtake Alison’s blog, yet I’m curious if anyone will agree with me about the added cost of shipping AAC. It cost perhaps $10,000 to ship the AAC from FL to upstate NY for my duplex; higher now. That is the added cost for a building envelope that is airtight, can’t burn, can get wet and dry out, isn’t food for any pests, is lightweight yet provides thermal mass and some thermal resistance, has a small global impact, and doesn’t support mold. Compared to stick building, what is the health and construction cost of mold remediation? Of a fire, including water damage even if extinguished quickly? A termite infestation? Of oversized mechanical equipment to compensate for a leaky envelope? I’m not a sane builder–I’ve built or renovated (never again) every house I’ve owned as if I’ll be there forever…and inevitably move on to another opportunity. I don’t recommend it as a way to earn a living. For another opinion, here is Alex Wilson’s take on AAC from his visit to my previous “Woodstock Passive House,” published in Germany–where this is routine: https://www.aac-worldwide.com/category/news/benefits-of-autoclaved-aerated-concrete-a-personal-experience-1823
Not gross but odd and interesting: In a vented crawlspace I spotted something small and regular in the soil (yeah, no vapor barrier). Curious, I pulled it up and it was a ceramic figure of Joseph from a nativity scene. Thinking it might have been lost by the homeowners, I showed it to them. They looked at each other and one asked me, was it head down in the ground? Why, yes, yes it was. They laughed. It wasn’t theirs, but they were familiar with a superstition that if you want success at selling land, you bury a figure of St. Joseph head down on the property you want to sell. Who knew?
Happy Holidays, all!