Buildings

Air-Tight and Leak-Free

Q: I'm worried that my new house might be too tight. Doesn't a house have to breathe or it will rot? Is there any way to tell whether a house is too tight?

A: This is one of the most confusing and least understood aspects of home-building today. It is also one of the most important. One problem is that several issues have gotten mixed up in people's minds.

To begin with, houses don't breathe. People breathe. Dogs and cats breathe. Parakeets breathe. Houses don't breathe. So people, dogs, cats, and parakeets need a steady supply of oxygen in order to be healthy.

When people talk about houses needing to "breathe," what they are usually talking about is the need to get rid of moisture from the house. If moisture gets into the different parts of the building and can't get out , various problems can occur, including the house "rotting."

According to this logic, if we build leaky houses, we'll get plenty of oxygen for the people and pets, and all the air flowing through the house will carry excess moisture away. As a bonus, all that air flowing through the house will also get rid of odors, cigarette smoke, chemicals out-gassing from the cleaning products and furniture, and various other pollutants we bring into our homes. Sounds pretty good, right?

Unfortunately, the "build it leaky" approach has a couple of serious drawbacks. Most of us aren't too comfortable in August with outside air at 90 o F and 90% relative humidity flowing through the house. Nor are we comfortable with outside air at 20 o F flowing around us in January. And most of us have lots of things we'd rather do with our money than use it to try to heat and cool the yard.

So, is there a way to prevent moisture problems, be comfortable, keep some money in your pocket, get rid of toxic pollutants, and have plenty of oxygen for your kids and their hamsters? And is there a way to know if we've done it? The answer to both questions is yes!

After studying these questions for years, Advanced Energy specialists, along with many building scientists from all over the country, concluded that the most sensible approach is to build the house as air-tight as possible and install mechanical ventilation to bring in a controlled amount of fresh air and to remove moisture and other pollutants.

While it may sound crazy at first (why go to all the expense and trouble to build a tight house if you then have to ventilate it?), this approach puts you in control of your house instead of depending on random holes in the building. How much ventilation you need is constantly changing. If it's your poker night, the kids are having a slumber party, or your husband has four friends over watching the international championship competition of former athletes who bash beer cans on their heads while skydiving on motorcycles, then obviously, the need for oxygen in the house will be a lot higher than normal.

Similarly, if you've been canning tomatoes all day, doing laundry, and all six teenagers at the slumber party are taking 45-minute showers, the need to get moisture out of the house is quite high. Controlling the ventilation of your house enables you to respond to whatever's happening. Depending on random infiltration of fresh air to take care of things is often not enough, even during "normal" conditions.

Testing is the only way to know how tight your house is. The most common testing method is with a "blower door," a large calibrated fan that can be used to measure the tightness of a home. AEC has trained over 200 heating and air conditioning technicians from all over North Carolina how to use this equipment. Many utilities have blower doors, as do weatherization crews. In most communities in our state, there is now someone nearby with this equipment and the ability to use it to measure the leakiness of your house.

A ventilation system doesn't have to be complicated or expensive. At a minimum, use high quality exhaust fans in the bathrooms and kitchen, and make sure they are vented clear to the outside (not into the attic). In smaller houses, good, quiet, variable speed exhaust fans may be all the ventilation system you need. Other systems are ducted into various rooms from one central fan, or are hooked directly into the heating/cooling ductwork.