Buildings

Keep It Tight and Vented

Q: One of the builders we talked with makes a big deal about building the house very tight, and then putting in a ventilation system. This doesn't make sense to us. Why go to all the trouble to seal up the house in the first place if you're just going to bring in extra air?

A: This is one of the most confusing aspects of home-building today. On the one hand, many builders and heating & air conditioning contractors believe that putting in the effort to build a really tight house is either not worth the effort or is actually unhealthy. On the other side, there is a growing list of medical and public health researchers, doctors, and a small, but increasing, number of builders and HVAC contractors, who are convinced that conventional ways of building houses are making people sick.

As usual, consumers are caught in the middle. We are bombarded by a seemingly endless stream of media reports about the latest discoveries of things in our surroundings that might make us sick, or even die. Instead of simply choosing the color, nap, and durability of the carpet for our homes, we're starting to wonder about dust mites, mold spores, volatile organic compounds, and other things we never heard of a few years ago.

People selling things from air filters to duct cleaning to air fresheners to vacuum cleaners are all trying to capitalize on the growing anxiety about the quality of the air in our houses. Many of us respond by choosing to ignore the whole thing. Our grandparents didn't worry about this stuff and they were okay, so this must be just another rip-off!

Unfortunately, our houses are very different from our grandparents' houses. They are much tighter and better insulated (and, for the most part, much more comfortable). We fill them with our stuff, which is made of tens of thousands of chemicals that didn't even exist in grandma's day. We use a wide variety of cleaning products and pesticides which grandpa never heard of. We add all these products to the "traditional" pollutants — moisture, carbon monoxide and other products of combustion, tobacco smoke, dust, mold and mildew.

There is no way that all of these substances, many of which "out-gas" into our homes, can be tested in all the possible combinations we create every day, to see if they are safe for us or our children or our elderly parents or grandparents. We know that a few people have their immune systems so compromised by something in their external environment that they cannot live in a conventional home at all anymore. What we don't know yet is whether these folks happen to have a rare disease condition, or whether they are simply a little more sensitive to these things than the rest of us, and perhaps — like the canaries in the coal mines — should be viewed as a warning.

Given all of this, what's a reasonable person to do when building a new home or trying to improve an existing one? The best discussion of this issue I've heard is from John Bower of the Healthy House Institute. John describes four strategies: Elimination (or Source Control); Separation; Filtration; and Ventilation.

The first thing to do is to eliminate pollutants from your home. This might include using products that don't contain formaldehyde, or eliminating combustion appliances that are not directly vented to the outside. Obviously, if something is not there to start with, you don't have to worry about it.

Some things, though, are necessary, even though they might be potentially harmful. Insulation is a good example. Most types of insulation cause respiratory problems in some people. No one advocates eliminating insulation. But by carefully sealing the sheetrock between the insulation and the house, we can essentially remove it as a problem. Another example of separation is to have a storage area for various household chemicals that is separated from the house. This can be an airtight cabinet with a tiny exhaust fan that comes on when you open the door, or it can be a totally separate shed out back. Storing these chemicals in the basement or garage where the air handler or furnace is located is not separating them from the living space.

Since most people have some form of forced air heating or cooling system, a good filtration system can be helpful. If that's your only strategy, however, it would take an enormous and very expensive filter to clean all the pollutants out of the air. Make sure any filter doesn't interfere with your existing heating and cooling system.

Finally, there are some things that only ventilation can do. One of the most important things you can do to improve your indoor air quality is to reduce the amount of moisture in the house. Local, or "spot," ventilation is very effective for removing moisture from bathrooms and kitchens. But it works only if it actually moves some air, is ducted to the outside, and is used on a regular basis.

A bathroom fan needs to be capable of removing at least 50 cubic feet of air per minute (cfm). Typical bathroom fans are so noisy and irritating that people rarely use them. They are usually rated at about 50 cfm, which means that by the time ducts and dampers are hooked up they really pull about half that amount. In the kitchen the range hood, as installed, needs to move at least 100 cfm, and it needs to be ducted to the outside. Spending some extra money to get a high quality, quiet unit for both the bathroom and the kitchen is well worth it.

In addition to removing moisture, we need ventilation to provide oxygen (fresh air) for people. While during some parts of the year we can get all the fresh air we need by opening up some windows, this is not totally reliable. If there is no wind, there won't be any air moving through the windows. And in the summer if we open windows, we let in lots of moisture. There are a number of good systems now on the market, some of which include a dehumidifier for the summer.