Fumes, odors, and gases from your attached garage can find their way into your living space and affect indoor air. Cars, mowers, paints, and lubricants contain or generate substances that can enter your home through open doors, gaps around closed doors, ducts, and other wall and ceiling penetrations. A Canadian study published in 2016 found measurable quantities of benzene (a gasoline-related pollutant) inside houses with attached garages, while finding little in those without a garage. Garage-generated carbon monoxide can even leak into your home and trigger carbon monoxide detectors. Fortunately, you can take a few steps to keep your indoor air quality free of these substances.
Keep the Garage Air Clean
Avoid running your car, motorcycle, chainsaw, lawnmower, or any other gasoline-powered item any longer than absolutely necessary while in the garage. 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 allow fresh air in.
When possible, avoid placing mechanical systems such as gas-powered water heaters and furnaces in the garage.
Seal the Gaps
Fumes often find their way into your home through gaps. This is something that is easy to take action to prevent. Assess where there may be gaps from your garage into your home and use inexpensive supplies such as weatherstripping, caulk, and spray foam to address them.
Make sure the door leading from the garage into the house closes tightly and proper weatherstripping is applied. If the weatherstripping is worn, replace it.
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. While this will be a larger project, it will pay off in not only protecting your indoor air but also making your garage more attractive and adding to the value of your home.
Keep the Door Into the House 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. Alternatively, 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.
Store Chemicals Safely
Make sure all containers of potentially dangerous substances are sealed. Don’t let cans of paint thinner, solvents, and other liquids sit uncovered. If you can smell any chemicals, it means that fumes are in the garage air. Not only are you breathing them in whenever you are in your garage, but they can also enter your home.
When storing a few items, think about getting a plastic bin with a sealable lid or a dedicated ice chest to use to store them. This will add an additional layer of protection.
If you store many potentially volatile substances in your garage, consider buying a lockable chemical storage cabinet. This will help ensure kids and pets don't access them and spill them.
Vent Your Garage 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.
Install a Carbon Monoxide Detector
Make sure your home has at least one carbon monoxide (CO) detector mounted. If you're curious about the CO levels in your garage, mount one out there, too, at least temporarily. It might be interesting to see if it goes off on a regular basis. If it goes off when you have not been running your vehicle in the garage, it could be a sign of a dangerous issue with your furnace or gas water heater. Although it might be irritating, it might even save your life.
Choose a Detached Garage
If you're planning to build a new house or garage, give some thought to making the garage fully detached from the house. You will keep odors, fumes, noise, and fire hazards separate from your main residence.
Mallach, G. et al. Exhaust ventilation in attached garages improves residential indoor air quality. International Journal of Indoor Environment and Health, 27(2), 2016 doi:10.1111/ina.12321