Why Mold Is More Common in Homes Today Than 100 Years Ago

Why Mold Is More Common Today Than It Was 100 Years Ago

"They don't build them like they used to."

I hear this from homeowners all the time, usually right after they find mold in a house that is only a few years old. And they have a point, a lot of homes built 50 to 100 years ago did not have the mold problems we see now. Mold, at the scale we see it in new construction, is a fairly new thing.

But the answer is not to go back to building the way we used to. We may not have had a prevalence of mold illness, but we sure had structural and thermal performance issues. It wasn’t all sunshine and rainbows building homes 50 years ago.

Older homes were not better built. They were built differently.

Let's be honest about older homes. Most of them did not have the structural integrity we expect today. They were not energy efficient. There were drafts everywhere. Air moved through the walls constantly, in the winter and in the summer.

What they did have was durable, forgiving materials. Solid wood framing. Solid wood baseboards and casing. Full plaster walls. No MDF, no particle board, no paper-faced drywall.

So an older home was strong in its materials but weak in its performance. When a wall got wet, the air moving through it helped it dry out. And the materials inside that wall could handle getting wet and drying again without turning into food for mold.

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Today, code requires a high-performing home

Building codes today require high energy efficiency and airtightness. We fill the walls with insulation. We set airtightness targets. We seal the house up so we are not paying to heat and cool the outdoors.

That is a good thing. But, once your walls are insulated and your home is airtight, you no longer have the option of a "drafty but fine" house. Your home has no choice but to be a high-performing home. The code has already decided that for you.

And a high-performing home is less forgiving. There is far less air moving through the walls to dry out moisture when it gets in. Water from a small leak, a poorly flashed window, or everyday indoor humidity has fewer ways out.

The three elements of a high-performing home

A high-performing home needs three things working together:

1. Energy efficiency - insulation and an efficient envelope.
2. Airtightness - controlling where air moves in and out of the home.
3. Durable, high-performance building materials - materials that can handle moisture without breaking down or feeding mold and are providing a robust line of defense against water intrusion.

Building code takes care of the first two. The third one is where most homes fall short.

Most builders deliver two out of three. They meet the energy code and the airtightness requirements, and then fill the walls, floors and finishes with the cheapest materials that pass inspection: paper-faced drywall, MDF trim, particle board cabinets. Materials that do not hold up when moisture shows up.

When you are missing that third element, the home has an opportunity to fail. And in a tight, insulated home, failure usually looks like mold and is happening sooner and sooner in new builds.  

So what do you do about it?

The answer is not less efficiency. If your home is going to be efficient and airtight, then the materials need to be chosen based on the build performance. A few places to start:

• Ask about the materials behind the finishes. What is the wallboard? What are the baseboards, casing and cabinet boxes made of? These choices rarely come up in a design meeting, and they matter.
• Look for moisture-tolerant options in the places that get wet. Bathrooms, laundry rooms, kitchens and exterior walls are where material choice matters most.
• Plan it early. Material strategy belongs in the design phase, not in a rushed decision on site when a crew is waiting. Thoughtful planning of water, air and thermal control layers is best to happen during the architectural stages.
• Make sure someone is checking the details. Great materials still need to be installed correctly, especially around windows, roofs and anywhere water can get in. I live by the motto “trust but verify."

Old homes had durable materials but no performance. Most new homes have performance but not durable materials. A healthy home needs all three elements: energy efficiency, airtightness, and materials that can handle what a tight home asks of them.

So the next time someone says "they don't build them like they used to," you can tell them: they don't. We build homes that are much tighter and much more efficient. We just need to finish the job with the right materials.