Last Updated: Feb 12, 2021
I am a healthy home consultant and, as such, have devoted my career to making sure people's homes are as healthy as possible. After all, we spend 90% of our time indoors. I've written articles devoted to many parts of the house, including kitchens, bathrooms, foundations, and even ductwork. Since we do not normally live in garages, this might seem like an odd topic to cover. But the fact is, over 80% of new homes have garages, and most of those are attached to our homes directly—and they do affect our health.
This home construction trend was not always the way. We used to park outside, even in cold climates, or use detached garages. In the late 1960's we used carports as open-aired, covered solutions. Now, some view garages as part of our driving culture's status symbol, with homes having attached 2 or 3 car garages being standard. But is this trend healthy?
The short answer is no. A healthy garage does not exist, unfortunately. We know this intuitively, as we put our smelly things in the garage: the car, the gas for the lawnmower, the central vacuum canister, paints, household chemicals, and more. But just because we put something in the garage does not mean it is really out of our homes.
An attached garage is unhealthy, partly because of air movement and air pressure. Hot air rises, and it also expands. Our garages are typically positively pressurized, meaning they are full of expanded air. The reason is that the driveway is warmer than the yard due to the black asphalt, concrete, or gravel surface being warmer than the grass in front of the house. This warm air is drawn into the garage, positively pressurizing the space.
Add to this the car itself. Idling for two minutes, even with the garage door open, will exceed the safe carbon monoxide levels in the space. The same research also states that it will take over eight hours to remove all of the garage's combustion and hydrocarbon products. Which is, unfortunately, about the same time you return home from work and fill the garage with more carbon monoxide. You then depressurize the garage by opening the interior door, pulling all of the chemicals quickly into the house.
The problems do not stop at the entryway door into the house from the garage. Low-level leaking of carbon monoxide and other combustion products can also flow through the leaks in the garage wall and ceiling - and migrate into the home. This risk is amplified in living spaces above the garage, like bedrooms. Low-level carbon monoxide levels could trigger your detector hours later inside the house.
The easiest fix? Do not attach the garage to the house. This step will always be the safest. The earliest version of LEED Homes, which came out in 2008, awarded one LEED point for homes with detached garages. If you must attach the garage, do not build living space over the garage. Ideally, do not put an entry door in the garage. Instead, install a vestibule with double doors, which can work great for a mudroom, or a breezeway, between the garage and the house to reduce contaminant spread properly.
Designing and building cross ventilation in the garage is a great design strategy. The airflow will then be able to go up and out the opposite wall through an open soffit or vent. This strategy also reduces the pressure drive into the home through the entry door.
For homes that already have attached garages (and there are a lot of them), the garage must be airtight. This is a code requirement in new construction, but your home may not be up to the current code. Taped wallboard on all surfaces, especially the ceiling, if living space is above, is necessary.
If you want to make the garage nice and neat and hang things on the walls:
The entry door should also be airtight, with good weatherstripping in place on all four surfaces of the door edges. To ensure the weather stripping is working:
Also, automatic door closers are code requirements now and are an excellent upgrade for the older garage. Door closers help ensure that the house's door is never propped open while working on the car.
Do you have your central vacuum canister installed in your garage? This exhausts fine particulate that the filter doesn't capture. That fine particulate bonds with the petroleum products, creating bigger, meaner toxins that can enter the home. Clearly, this is not ideal. The solution is to ensure that your central vacuum exhausts outside of the garage - an easy fix. Likewise, if you have any other vents into the garage, like dryer vents, they should also exhaust outside.
I would bet that you don't need all of those chemicals in your garage. If you are storing them there, where it's "safe," the simple truth is that if they are that toxic, you should not use them. There are healthier options for almost all household chemicals. If you need to keep some, put them in a vented locker, exhausting outside, just like you might do at the shop.
The above recommendations are low energy, passive suggestions. Doing them once and maintaining them is the first, more straightforward step. For active solutions that require power, exhaust fans are an excellent idea. Install a properly sized exhaust fan, typically a bathroom type fan, hard-wired to the garage door opener. Every time the garage door is powered up or down, the exhaust fan should run for 15 minutes. This system will dramatically reduce the combustion products and hydrocarbons in the garage and make things much healthier. You can easily add this solution when building new, as well.
Some of these details apply to those driving or thinking about purchasing an electric car, but not all. Notably, the carbon monoxide from combustion will be absent.
Other garage-related issues could affect your family's health, like:
Whether you store these items or not, your vehicle's tires may have picked them up along the way and dragged them into your garage. The bottom line is that it's essential to remember attached garages add many air quality risks to your home. Addressing the issues will help you improve your home's indoor air quality and your family's overall health.
Stephen Collette is a Building Biologist, Building Science Consultant, LEED Accredited Professional, and a Heritage Professional. Stephen is the owner of Your Healthy House and lives in Lakefield, ON with his wife and 2 daughters.