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From The Field · A True Story

Black Mold, a Leaking Window, and a Boy in the Hospital

Early in my career, I sold home improvement in the Washington DC and Northern Virginia area. Across the river from Southeast DC there's a neighborhood called Anacostia. It's a lower-income community, and property values there are low, but here's what a lot of people don't know: many of those folks own their homes outright. The reason is that the home has been passed down, sometimes seven or eight generations. That house is often the only asset a family has ever had, and every time it changes hands the message goes with it: protect this home, it's all we have. People in that position will do whatever they can to hold onto it.

I went to see a homeowner there one day to look at her windows. I want to tell you how that visit went, because it changed how I think about this work, and it's the reason I take deferred maintenance as seriously as I do.

Listen first, then look

When I sit down with a homeowner, most of my time is spent asking questions and listening. That's the best way to find out what problems they believe their home has. In this case, the windows had already been replaced once, roughly ten years earlier. Her father did it before he passed away, and he meant well, but the work wasn't done well. The windows were drafty, they didn't operate right, and a few of them looked to her like they'd been letting water in. That was her worry.

Once I understand what a homeowner wants to fix, I do a full inspection to see whether what I find lines up with what they're feeling. I always start outside, taking photos and video as I go, and then come back in. Starting outside is how you find root causes, because the outside is almost always where the interior problem begins.

What the outside told me

This home was brick and block construction, like a lot of the older homes down there, and with age the masonry often needs help. Outside, I found several windows that had been put in with a pocket installation, meaning the old frames were never removed. The frames around those windows and the masonry openings had both deteriorated, and the caulking from the previous company was either gone or coming apart. That's where my gut told me her water was coming in, four windows in particular.

If you want the plain mechanics of why that kind of install fails, I wrote about it in insert versus full-frame window replacement. The short version: a pocket install is only as good as the frame it nests into, and hers were shot.

Three rooms

I went back inside and asked her to walk me to those rooms while I explained what I'd found and what it could be causing. She looked relieved, because I was confirming what she already suspected. First the master bedroom, where there was some water damage on the plaster, nothing that couldn't be repaired. Then the guest bathroom, where the shower tile was cracked and the window clearly wasn't sealing, though I couldn't see much behind the tile.

Then we went into her grandson's room.

There were two double-hung windows side by side, and his bed was pushed right up against them. I knelt on the bed, pulled back the curtain to get at the windows, and I saw it immediately: black mold on the interior sill, inches from where his pillow sat. She was standing in the doorway. I turned around and told her, this is a serious problem. Water has gotten into the wall, and it's grown black mold right here on this sill.

She looked confused. She said, I thought that was just dirty. What is black mold?

The next ten seconds

I told her the truth, which is that mold like this is nothing to wipe away and forget. Exposure to damp, moldy conditions indoors is linked by the CDC to coughing, wheezing, and respiratory symptoms, and people with asthma can have severe reactions to it. I told her it can be especially hard on someone with asthma, and that's when her world came apart.

She broke down sobbing. I didn't understand at first. When she caught her breath, she explained: her grandson wasn't home because he'd been in the hospital for three days with respiratory problems. He has asthma, and no one had been able to figure out what was setting off his coughing and wheezing. It was the black mold, growing on a windowsill inches from where he laid his head every single night.

What we did

We went to work. We pulled out the old, damaged window frames, sealed up the masonry underneath, and replaced the interior sills. HEPA cleanup was included, and we used lead-safe installation practices throughout, which matters in a home that old. Then we installed new windows that actually sealed. We found a payment plan that fit her monthly budget, and for a few hundred dollars a month, we protected her home and her family.

I got a Christmas card from that woman every year I was still in DC.

Why I'm telling you this

Deferred maintenance on a home isn't only about the structure. A drafty window feels like a small thing you can put off. But water that gets past a failed window doesn't stay a small thing. It gets into the wall, and sometimes it becomes something that affects your life and the lives of the people you love.

It's no different here in Wisconsin. Our freeze-thaw winters drive water into every gap a failed seal or a bad install leaves open, and it works the same way behind the wall. If you've got a window with staining below it, a draft you can feel, or what looks like dirt on the sill that won't quite wipe clean, please don't wait on it. Those are the signs worth acting on.

When we come out, we start outside, we find the root cause, and we tell you straight what your home needs. That's the whole job. You can see our window options or book a free in-home visit whenever you're ready.

TJ Moon, 22 years in residential exteriors

TJ has spent more than two decades walking homes and sitting at kitchen tables across the country, from century-old brick homes in DC to the metro here in Wisconsin. He's seen firsthand what deferred maintenance really costs, and it's the reason he starts every inspection looking for the root cause, not the easy sale.

Common Questions

Window leaks, water, and mold.

Can a leaking window cause black mold?

Yes. When a window leaks, water gets into the wall cavity and the framing around the opening. That trapped moisture is exactly what mold needs to grow, and it often shows up first on the interior sill or the wall just below the window. A stain you think is dirt can be the early sign of a much bigger moisture problem behind the wall.

Is black mold from a window leak dangerous?

It should be taken seriously. The CDC reports that exposure to damp and moldy indoor environments is linked to coughing, wheezing, and respiratory symptoms, and that people with asthma can have severe reactions. It's not something to wipe away and ignore, especially in a bedroom or anywhere someone sleeps.

What is a pocket window installation and why can it fail?

A pocket or insert installation sets a new window inside the existing frame without removing it. It's faster and cheaper, and it works fine when the existing frame and the wall opening are sound. It fails when the old frame or the masonry opening is already deteriorating, because the new window gets set over a bad foundation and water keeps finding its way in behind it. More on that in insert versus full-frame replacement.

How do you fix a window leak that has caused mold?

You have to deal with the water first, not just the window. That means removing the failed window and frame, repairing and sealing the opening underneath, safely cleaning up the affected materials, and replacing the damaged sill or trim, then installing a new window correctly so water can't get back in. Covering it up without fixing the source only hides the problem until it comes back.

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