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  • Writer's pictureSquare One Inspections

Attic Mold Is Manageable. That’s right. I said it.

Buyers are easily intimidated by mold stains in the attic. Mold should be taken seriously, but its typically very manageable. Don't rush to make a decision. Process all information and then decide.

Yesterday, I inspected two homes that had or will have mold. A 1998 house followed the proper bathroom venting code of the time and now has attic mold. A 2023 build did not follow current bathroom venting code and WILL have mold. This is just one more reason to have home inspections on new houses.

Below shows the attic sheeting for the same house. The left is the far end, away from bathroom vents and attic hatches. The right has mold found directly over the bathroom fan.

Why Would Contractors Do This?

In most cases, It’s not their fault. They were likely following the building code. The 2003 building code was the first to require bathroom venting to the outside. Before that, venting in the attic was not only acceptable, it was encouraged. This is why we see so many homes built between 1970 and 2010 that have attic mold (including my own). To make matters worse, most municipalities have a delay between when the code is written and when it’s adopted. In 2023, Maine only requires the 2015 code to be followed, at a minimum. The 2018 and 2021 codes are available, but not yet adopted statewide. It’s entirely possible that your home built as late as 2010 did not require this venting change. It all depends on where you live and when your town adopted each code revision.

In the 1970s and 1980s, homes started to become energy efficient. They were built tighter with improved insulation. This brought unintended consequences of trapping heat and moisture that would otherwise escape, hence the code revisions. Also, I rarely see a 1960s or earlier build that had a bath fan installed at construction. So, we installed fans to send heat and moisture into attics that are now built to leak less air…whoops. Bath venting supplies two main ingredients for mold to grow: moisture and heat.

Details, Details, Details….

Its not a simple as having your bath vent not terminate in the attic, it’s how it vents to the outside. I said “TO” the outside, not “TOWARDS.” Big difference. TO the outside means the air vents to daylight and has little obstruction from a vent cap. Vent caps keep birds and snow from entering an opening on the outside of the home. TOWARDS is nearly as bad as venting directly into the attic. It points the air in the right direction, but doesn’t quite finish the race. Blow through a straw and 100% reaches the other end. From an inch away, blow at a straw. Not much gets to the end, does it? TOWARDS doesn’t work. A contractor may disagree because that is what they have always done. Well, they leave the site after construction. I see the home 5, 10, even 40 years later after the damage is done.

Below is a new home without a visible vent cap. Being curious, I used my thermal imaging camera to find a heat bloom (yellow) at the soffit vent above the bathroom window (center of the photo) after running the fan for 10 minutes. I was able to confirm the vent terminates INSIDE the soffit and never makes it outside. If the heat is trapped inside, so is the moisture.

A soffit vent is a long strip that you can see in many homes (not all) under the eaves. It’s a 4” wide strip that runs the length of the house on both sides. The intent is for this to be a source of fresh air while the ridge vent at the top of the home vents the accumulated hot air (warm air rises). This attempts to keep the attic the same temperature as the outside, minimizing condensation from hot and cold meeting on the roof of your attic. Many bathroom vents point at this vented strip from the attic side, expecting bathroom air to reach the outside. The vent is a bottleneck and only allows about 15-20% to escape. The rest reflects towards the attic for Mold Thanksgiving.

My Home Inspector Found Mold in My Attic. What Do I Do?

1. Make sure your real estate agent also knows about the mold

2. Have a mold remediation company create an estimate for removal and cleaning

3. Have a contractor modify bathroom vents to exhaust TO the outside, with a vent cap

4. Confirm resolution: Turn on the fan and the louvers on the vent cap should open.

5. When all the work is done, insulate and seal (caulking strip) the attic hatch.

What You Need to Take Away:

  • Always have a home inspection, even new homes.

  • Don’t run from mold in the attic. Attack the problem and then decide.

Thanks for reading,

Matt and Matt

Square One Home Inspections, LLC


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