Attic ventilation has been a controversial topic among building contractors. And it gets even dicier when it relates to the garage. Many contractors recommend you ventilate the attic, while others deem it unnecessary. In this post, you’ll learn whether you need to vent your garage attic or not, based on your situation.
According to the International Residential Code, it is not required to vent an attic, and that includes the garage attic. However, if you plan to insulate the garage attic floor, most building codes require you to vent the attic. It’s also a good practice to vent a garage attic if it is used as a living space or workshop.
Garage roof and garage attic will be used interchangeably in this article. They are basically the same thing. We will take a look at the reason why attics are ventilated in the first place. After that, we will discuss why it may be unnecessary to vent the garage roof, and also the reasons to consider venting the garage attic.
Why are attics ventilated?
The main reason why attics are ventilated is to remove hot air trapped in the attic in hot climates. In cold temperatures, it allows hot, humid air transferred from the living area to escape. This prevents ice dams from forming.
If all of this sounds complicated, let me break it down for you. During the summer, or if you live in a hot climate zone, the sun rays hit directly on the roof. The room becomes hot in the process, and by the concept of heat transfer, the heat is transferred from the roof into the attic.
For an unvented attic, this heat continues to build up over time as the sun continues to shine throughout the summer. That’s because there is no place for the heat to move.
However, if your ceiling is not insulated, all that heat built up in the attic is transferred to your home, making your living area hot and uncomfortable to be in. To fix this problem, many homeowners will simply turn up the air conditioner. But that only temporarily fixes the problem because the heat keeps increasing, which means more work on your air conditioner.
This will result in increased electricity bills for that period. It gets worse if your HVAC system breaks down. Because your home literally becomes an oven — sweltering and unbearable to be in.
Having a well-ventilated attic will prevent all of this from happening. There will be no heat trapped in the attic. That’s because the vents will allow passive air to blow off and exchange the hot air inside the attic. This will keep your ceiling cool and room temperature comfortable.
During the winter or in a cold climate, the situation is totally different. The unvented attic becomes very cold. In this case, hot, humid air from the heater system is actually transferred from your living area into the attic, through the ceiling. This happens when the ceiling has no vapor or air barrier.
When the hot moisture air meets the attic’s cold air, it condenses the water in the air, and this is a recipe for disaster. Let me explain.
Condensed water in the attic can cause the wood used for the roofing to rot, and worst-case scenario, you will have to redo the entire roofing of your home. That can be very expensive. The condensed water will also help molds and mildew develop in the attic, causing a musty smell in your home. Another problem is that when there is snow on the roof, the hot air in the attic will cause ice dams.
However, if the attic is ventilated, all the leaked hot, humid air from your living area will escape your home through the vents. This means there will be no condensation in the attic, leaving your roofing with no issues.
I hope this gives you a foundation on why attics are ventilated. Now let’s talk specifically about garage attics and why you may not need to vent it.
Why garage roofs or attics don’t need to be vented
The garage attic is just like any other attic. Everything we have already discussed about attics applies to the garage attic as well. But here is the difference.
The garage is a utility room.
The International Residential Code (IRC) is a set of rules, regulations, and best practices for ensuring homeowners’ personal safety and security. These regulations must be followed by building contractors, plumbing, electricians, and all other disciplines to make sure residential homes are safe to live in.
Under a section in the code they call Occupied Spaces; the garage is categorized under Type U Occupancy. I explained this concept in detail in this article. I recommend you check it out if you want to learn more.
The “U” in the Type U Occupancy stands for Utility. Essentially, the garage is considered as a utility room, according to the IRC. According to the code, utility rooms do not require ventilation. This is why most garages have no ventilation. It’s because it’s a matter of choice for building contractors to ventilate a garage or not. The garage is simply a space for storing equipment and accessories.
Besides, ventilating an attic, in general, is also a matter of choice and is not required by law. This is why attic ventilation is a controversial topic, even among experts.
So, yes, your garage will be hotter in the summer and colder in the winter because of an unvented garage roof. But if you use your garage to store your vehicle, just as it was designed for, it wouldn’t matter. That’s because you wouldn’t be spending a lot of time there to feel uncomfortable anyway.
The garage is mostly not part of the HVAC system.
As I mentioned earlier, the garage does not require to be vented. For this reason, the garage is mostly not made part of the home’s HVAC system.
Why am I making this point? Let me explain
Venting your home’s attic has an impact on the temperature condition in your living space. The hotter the climate gets, the hotter your living area gets if the attic is not vented. This means it will cost you more to cool your home. The colder it gets, the more expensive it gets warming your home.
This is not the case for attics in the garage, however. Regardless of the temperature condition in your garage, it won’t affect your electricity bills. That’s because the garage is not part of the heating or cooling system of your home.
Now let’s take a look at some compelling reasons why you should ventilate your garage roof.
Why you should consider venting the garage attic
As we have already discussed, if you are going to use the garage as your vehicle storage room, there is no need to vent the garage attic. But there are still good enough reasons to vent the garage attic. Let’s discuss it.
1. Attic Vents are required for insulated attic floors
Please pay attention to the next sentence. According to Section R806.1 of the 2015 International Residential Code, it is required to vent an attic when you insulate the attic floor or ceiling. And this is for a good reason.
Warm, humid air built up in the attic will have no place to escape through when the attic floor is insulated. And this can damage your garage roof over time. It can lead to rotten wood in the attic, or increase mold growth. Obviously, you don’t want that to happen, because it can lead to expensive home repairs.
As required by code, for every 300 square feet of the attic floor, there has to be a 1 square foot of roof ventilation
2. Ventilate the garage roof or attic if you are repurposing your garage
The garage is not what we originally thought it was. Not a lot of homeowners use it as a parking space only. Many homeowners use the garage for a variety of things. Some people have turned theirs into a laundry, others have converted it into their offices, some people use it as a playroom, a gym, or as a storage space for rarely used items and appliances.
If you have repurposed your garage or you are planning to, there is a high probability that you will be spending a lot of time in the garage just as you would in your living area. This means you have to treat it as a regular room in your house, and not as a utility room. You want to be as comfortable as possible in the garage if you will spend a lot of time there.
This means you have to consider venting the garage attic, to make the room temperature nominal in all seasons and climates. The garage, without any form of ventilation, is very uncomfortable to be in, generally.
The garage temperature and traces of exhaust fumes in the air don’t make it a habitable place to be in for a long time. Not unless you ventilate it well enough. You should also consider insulating the garage ceiling. More on that later
3. Venting the garage attic will reduce garage heating and cooling cost.
Although, not a lot of homes have their garage included in the HVAC system. But there are a few that do. Some homeowners also felt the need to buy garage air conditioners and heaters along the line to keep garage temperature better.
If your garage’s attic is not ventilated, you will probably spend too much on electricity heating and cooling your garage. As we have already discussed, hot air in the garage attic during the summer will seep into your garage, meaning you have to crank up the garage’s AC to keep the place cool.
With the attic well ventilated, you reduce the heat seeping into your garage, putting less stress on your cooling system.
If you want to improve your garage roof and prevent any future damages, here are the two things I recommend you do.
Seal all air leaks on ceiling and roof
Moisture can diffuse through your garage ceiling into the attic and cause mold growth in the attic. That is true. However, one thing that gets a lot of moisture in the attic is air leaks. I explained this concept in detail on my post about vapor barriers in the garage. I highly recommend you check it out.
Essentially, if you have an airtight garage ceiling and a roof with no leaks, there will be less to no moisture in the attic to cause any problem. When done right, there will be no reason to vent the attic. So, carefully inspect and seal any hole in the ceiling and roof leaking air into the attic.
Alternatively, you can install an air barrier in the garage ceiling. Just as the name depicts, an air barrier is a material that prevents air from passing through it. Installing this on your ceiling will ensure no air, whether warm or cold, enter the attic. There will be no need to vent the attic when you get this right.
CertainTeed’s Membrain “Smart” Vapor Retarder (on Amazon) is an excellent air barrier you can install on your garage ceiling or attic floor. This will block all air leakages in your ceiling and prevent air diffusion into the attic. As you can already tell from the name, it doubles as a vapor retarder as well. So it blocks moisture in your garage from diffusing through the garage ceiling.
Insulate the garage ceiling
If your goal is to keep your garage in an excellent overall temperature, I highly recommend insulating the garage ceiling. This is essential if you are converting your garage into a living space.
Insulating your garage ceiling is an excellent way to keep the heat trapped in the attic from transferring into the garage. In the winter, it will also prevent any heat transfer from the garage to the attic.
In essence, insulation seals the garage from the roof thermally. This is incredibly helpful if you have garage heating or cooling systems. That’s because there will be minimal transfer between the attic and the garage, meaning you don’t have to crank up your HVAC system to compensate for the lost heat or air.
I recommend ceiling insulation for not only the garage but the entire house if there is an attic. That’s because it will save you a lot of bucks on electricity.
Just as the name depicts, garage ceiling insulation means adding insulation material to your garage’s ceiling. This can be done by adding it inside the attic itself, which is on the attic floor, which I recommend, or by adding the insulation material under the attic, that is, on the garage ceiling.
As I mentioned earlier, if you are insulating the garage ceiling, then it is required by code to vent the roof. Doing so will prevent damages caused by the heat trapped in the attic.
Although venting the garage roof is not needed if you only park your vehicle in the garage, it is required by code to vent the attic if you insulate the attic floor. It is highly recommended you vent the garage roof if you use it as a living space and want to keed the roofing in good condition.