Attached garages are convenient, but mounting evidence suggests that they're responsible for negatively affecting indoor air quality. Much of what we use our garages for -- like cars, mowers, paints, and lubricants -- contains or generates substances that are considered toxic. When toxic substances become airborne, they can easily migrate indoors.
It’s a bit ironic that we keep a floor mat by the door from the garage to the house so shoes can be cleaned of largely nontoxic items like dirt, yet we often take no such preventative measures regarding the air. Car exhaust, toxic chemicals, and volatile organic compounds are present in almost all garages at least some of the time. They can find their way into the house easily through open doors, gaps around closed doors, ducts, and other wall and ceiling penetrations.
A study involving 100 houses conducted by Health Canada found that those with attached garages had measurable quantities of benzene inside, while houses without attached garages had little if any benzene. Benzene is a gasoline-related pollutant. The study found similar results with other pollutants.
According to the U.S. Occupational Safety and Health Administration, long-term exposure to benzene can affect bone marrow and blood production. Short-term exposure to high levels can cause drowsiness, dizziness, unconsciousness, and death.
A survey of Minnesota houses during the winter of 1997 found that 74% of homes with carbon monoxide detectors that went off were triggered by CO leaking in from the garage. Other studies from Iowa, Colorado, and Alaska have found substantial evidence of garage-generated CO leaking into houses.
What to Do
Nobody wants to breathe toxic pollutants, especially at home. Fortunately, you can take a few steps to keep your indoor air quality safe, not something you should worry about inhaling. Here are some tips:
- Keep the garage air clean. Avoid running your car, motorcycle, chainsaw or lawnmower any longer than absolutely necessary while in the garage. Avoid placing mechanical systems such as water heaters and furnaces in the garage.
- Seal the gaps. Make sure the door leading from the garage into the house closes tightly and proper weather-stripping is applied. Seal all penetrations like ducts and wiring that lead into the house or the ceiling above the garage. Caulk and spray foam are good products for sealing these types of gaps.
- Finish the walls and ceilings. It's not uncommon in new houses for the garage to be left with open walls or with drywall attached but the joints not finished. Both these conditions allow garage pollutants to easily find their way inside. Garage walls and ceilings that are completely covered with drywall, with joints properly sealed with tape and compound, and with the surface primed and painted are much less likely to leak. They are also much more attractive.
- Keep the door shut. You often find yourself with full arms when you're entering the house from the garage. The result can be that the door remains open until you set the groceries down, or maybe you or the kids simply forget to close the door or fail to close it all the way. This can allow nasty fumes from the garage to enter the house quickly and easily. You can avoid this problem by installing a self-closing door.
- Keep the door open. Never start your car or any other internal combustion engine when the garage door is closed. When you do start the engine after the door has been opened, move it outside as soon as possible, then shut the door to prevent exhaust fumes from floating back into the garage. Shut your car off as soon as possible when you pull it into the garage and leave the door open for a few minutes to clear the air.
- Put a lid on it. Make sure all containers of potentially toxic substances are sealed. Don’t let cans of paint thinner, solvents, and other liquids sit uncovered.
- Vent it outdoors. If you spend a lot of time in the garage working with chemicals, paints, wood finishes, combustion engines or other such items, consider installing an exhaust fan that sends the smells and fumes to the outdoors. A decent bathroom or kitchen fan will be sufficient.
Make sure your home has at least one CO detector mounted. If you're curious about the CO levels in your garage, go ahead and mount one out there, too, at least temporarily. It might be interesting to see if it goes off on a regular basis. Although it might be irritating, it could be educational to learn that the air you're breathing in that space contains a toxic substance.
Finally, if you're planning to build a new house or garage, give some thought to making the garage fully detached from the house. In addition to largely eliminating garage pollutants from migrating inside the house, detached garages offer several other benefits.