Sophomoric humor aside, houses that “breathe” through air leaks really do suck — they suck air from all the wrong places. We call this uncontrolled or unintentional ventilation, also known as infiltration.
The Dangers of Uncontrolled Ventilation
Uncontrolled ventilation simply means that your house is “breathing” from the worst possible places, such as your attic or crawlspace. If you have kept up with this blog, you probably already know that ventilated crawlspaces are a bad thing. It is common here in Kentucky to have 25 percent of your home’s air pass through your crawlspace before it comes into your living space. That’s just plain gross!
Uncontrolled Ventilation & Your Crawlspace
Take it from me: I have spent the last 25 years in crawlspaces, and there is some really nasty stuff down there! Insects, rodents, feces, mold, mildew, and sometimes other hazards like asbestos are all present in the average crawlspace. You certainly don’t want 25 percent of your indoor air being contaminated before it even comes into your home for your family to breathe.
Crawlspace Encapsulation for Better IAQ
According to a report by the Wall Street Journal, the average home’s indoor air quality (IAQ) is three times as dirty as outdoor air. No wonder our allergies are off the chart in the US! And it doesn’t stop there.
If it were just about cleaning out the crawlspace and making it a healthier environment, we could recommend simple crawlspace encapsulation. This entails cleaning out the crawlspace, placing a heavy-gauge reinforced poly sheeting for a vapor barrier, insulating the walls, and leaving behind a cleaner, healthier home. Crawlspace encapsulation is by far the best way to address the crawlspace, thus improving a home’s air quality, making it more comfortable, and lowering utility bills; but it is only part of the answer.
Your Attic, Stack Effect & Negative Pressure
When a house is breathing, typically the attic dictates how much it’s breathing; and how much it’s breathing usually has an impact on where it’s breathing from. Houses on a basement, for example, do not breathe from a ventilated crawlspace. This causes what we in the building science community refer to as “stack effect.”
Stack effect is the same process that allows your fireplace to vent smoke. Hot air rises, leaving a vacuum-like effect behind it and pulling smoke up with it. This process creates a negative pressure behind it, because the air leaving the space gets replaced by air from somewhere. In today’s newer homes, fireplaces are required to have a fresh air vent to the outside so that we can control where that air comes from.
Attics often do not have controlled ventilation, so when the hot air vents out of the attic in the summer, stack effect creates a negative pressure in the house, typically from the crawlspace or basement. This negative pressure creates all kinds of problems because it pulls air from anywhere it can get it — gaps and cracks in the walls and foundation, leaking windows, and even the ground itself.
Two Homes & Their Risk for Radon Gas Infiltration
These next two charts compare two Lexington area homes we worked with this past summer.
Left: a tight home and minimal risk of radon gas
The house on the left was a tighter home where we spray foamed the attic and sealed all the leaks we could find in the basement foundation. It had a ventilated attic with a leaky basement. The red line at the top is gas being drawn into the home from the basement slab. You can see the home on the left only had a slight variation of about 1.5 PICO/L; this is a very good number that we are happy with.
Right: a leaky home and major risk of radon gas
The house on the right saw a variable of 18 PICO/L; this is a very bad number — almost 10 times as high as the tight home, and almost 5 times the recommended maximum exposure to radon. Just living in this home every day is the equivalent of smoking almost 2 packs of cigarettes a day in cancer causing lung damage! This home is literally sucking toxic radon gas out of the ground because the attic is creating such a negative pressure in the home.
This is another example of a contractor (in this case, the roofer) trying to add uncontrolled ventilation to a home without knowing the domino effect he was causing. Sure, he made the attic cooler, but only at a cost to the rest of the home. This house also had some mold and mildew issues that we think were also being caused by foundation air leakage bringing in too much humidity in the summer. All of this was caused by an oversized attic fan from a well-meaning roofer. Who would have thought a roofer could have that much effect on indoor air quality?
Instead of venting attics we should be encapsulating (fully sealing) attics. By closing the attic completely and insulating the roof deck(back side of shingled roof) we never allow the outside heat in and subsequently stop the greenhouse effect that increases attic temperatures to more than 140 degrees in the peak of summer. Not only does this stop the stack effect that causes the attic to suck on the basement or crawlspace it also protects any HVAC equipment that might be in the attic. A standard air-conditioner only cools the air approximately 20 degrees, how much of that is lost running 50 ft through duct work in a 140 degree attic? Encapsulating your attic and crawlspace together is the best way to control your home’s ventilation, we have a phrase “build it tight and then vent it right”.
Synergy Home’s Whole Home Approach
This is why Synergy Home takes a whole home approach. We understand the domino effect that can follow insulating and air sealing your home. Creating controlled ventilation, instead of relying on uncontrolled infiltration, can solve a multitude of issues in today’s homes. Indoor air quality, comfort, and high utility bills are all affected, and we have the knowledge and the skilled trade workers to fix these and other issues in your home. That’s why we say, “Is your home in sync?”