Monday, October 26th, 2015
Why DOES a house have to breathe?
Have you heard the old saying that a house needs to breathe? I’m in the business of making houses more air-tight (among other projects), and so I hear that a lot. First let me say that I AGREE, having a house that’s tightly sealed can cause lots of problems if certain challenges aren’t met properly.
Hmm… That didn’t come out sounding as clear as I had hoped. And certainly not as catchy as “A house needs to breathe.”
Let’s start at the beginning. Anything you do you keep the warm air inside your house longer… counts as energy savings. If you want lower bills, build your house like a space-ship – air-tight and well insulated.
The problem is the people (no offense intended to readers who are members of the species, of course). Everyday life produces humidity – whenever someone takes a shower, boils a pot of water, or even just exhales, moisture is added to the air. Unless we have a means of dealing with excess humidity, we’ll soon end up with mold, mildew and bacterial growth. If you seal a group of people in a humid, moldy, germ-filled box… you’re not going to make many friends. They actually have a term for this. It’s called “Sick Building Syndrome.” And it’s not just germs and biological nasties that cause it. Did you know that your carpets and cabinets were made with formaldehyde? Most are. Sofas, paints, laminates… We need a way to deal with indoor air pollutants and humidity.
So. Houses don’t need to breathe, they need "a means to deal with humidity and pollutants." Not really catchy, I’ll admit, but more scientifically precise.
If you want something catchy, the green building community is now saying, “build tight, ventilate right.” In other words, fresh-air ventilation lets us build better homes without worrying about a house needing to “breathe.”
You see, once upon a time, we relied on poor workmanship to supply us with enough fresh air in the house. Two or three hundred years ago, there was nothing WRONG with a drafty house. Windows open up in the summertime to let the breezes blow though. In the wintertime, a Franklin stove BLASTS heat out from the center of the house. Before bedtime, the fire is stoked up so high that you can barely stand the heat in the living-room. That heat spreads through the whole house. Huddle under your blankets, and get a dog or two up on the bed for warmth. Ever heard of a “three dog night?” That’s when it’s REALLY cold. If the stove couldn’t keep up with the cold weather, then you needed a bigger stove and more firewood.
The idea of heat RETENTION didn’t really come into fashion until the fuel crisis of the 70’s. We stopped building houses “the way my Grandad did,” and we started paying attention to the science of “buildings.” The blower door was invented. We started building houses with fewer drafts and more insulation. Tighter and tighter houses. Those who followed the science started building in air-quality solutions. Others who jumped on the efficiency bandwagon either got lucky or got into trouble. By the mid ‘80s, indoor air quality was a serious concern in many new buildings. It was 1986 when the World Health Organization coined the phrase “Sick Building Syndrome.”
Today, we have many options for handling indoor air quality and the “breathability” of a house. A blower-door test can precisely measure the infiltration and exfiltration rate of your house. There are official standards to be met. On one end of the spectrum a house might be a drafty waste of energy. On the other end, a house might require intentional ventilation. In the middle is the “Goldilocks” zone – not too tight, not too drafty.
OK. I’m going to get into trouble with the Building Science community for using the words “too tight” to describe a house. There’s no such thing as a house that’s too air-tight, so long as there is a solution for the air-quality concerns. And since tighter usually means more efficient, we should strive to bury that needle all the way to the left. It’s true, and I’d LOVE to live in that house. In the meantime, I’m going to be pragmatic when it comes to fixing up existing homes.