Ventilating your bathroom is a must, and part of the process has to include where the exhaust should be vented. To vent it discreetly, venting through either the roof or soffit can work well.
If your roof and soffit are about the same distance away from the bathroom, there are pros and cons you must consider for each process. Warm air’s natural movement, the weather, and water damage must all be considered to choose the best option.
There are advantages and disadvantages to both methods but ultimately, venting through the roof has more benefits. There are some exceptions, including houses with flat or low-pitched roofs and in situations where venting through the soffit is the shortest route.
Always Vent the Shortest Distance
The first factor that should be considered is if the roof or the soffit is closer. Venting through the one that is closer should absolutely be a priority, and there are three reasons for this.
The first reason is by far the most important. The shorter the duct, the more efficient the exhaust system. This is because the air traveling through the ducts loses momentum due to friction with the duct surface.
If the air moves through the ducts inefficiently, then the effectiveness of the system is compromised.
Slow-moving air has more time to cool, and cooler air holds less moisture. So, all of the steamy air that you are trying to get out of your house ends up condensing in the ducts and running back out of the bathroom fan.
The steamy air is also removed from the bathroom more slowly, which means you end up running the fan longer to clear the bathroom air. This results in higher energy usage and cost.
In addition, you are more likely to turn the fan off before the bathroom is completely steam-free, and you end up exposing your bathroom to the moisture and related damage that the fan was supposed to be preventing in the first place.
So, the shortest route is of vital importance. In fact, the length is so important that it is regulated by the IRC.
As a bonus, the installation of shorter ducting systems is easier and cheaper.
Venting Through the Roof
Advantages
First off, venting through the roof is more common than venting through the soffit of your home.
Because of this, contractors and other qualified professionals are more likely to agree to the job or do a better job of the installation because they’ve done it so many times before. There may even be a lower fee because of the ease of doing a well-known installation.
Even if you’re planning on installing the ducts yourself, a more common process means that more resources, like DIY guides and videos, will be available to you, making the entire process easier.
Since hot air rises naturally, it more readily follows a path leading upward and out through the roof. This can increase the efficiency of the exhaust process.
On a roof, there is little impeding the release and dissipation of the hot and moist air that could cause damage over time if trapped against the house. The air exits the vent and can immediately be swept away by the air currents blowing over the exposed roof.
Unless they have tall vent hoods, roof vents are often less visible and are, thus, more aesthetically pleasing.
Disadvantages
You can install flashing and caulk and seals, but a roof with a hole cut into it will always be more likely to develop leaks than a roof that is intact.
With rain and snow falling directly onto the roof and running down it (the heat from the exhausted air melts snow), the water can so erode away at the edges of the hole. It’s even worse with a flat or low-pitched roof because the water is more likely to accumulate.
Additionally, the running water can easily find its way into the vents themselves and leak out the bathroom fan.
The lovely angles that make it so easy for hot air to rise through also make it so easy for water to drip down, and it’s often dirty brown water that then stains your ceiling or walls.
Even if it’s not dirty, drips are slip hazards and increased moisture can lead to peeling paint, swollen wooded furniture, and rusty metal fittings.
Although venting through roofs is quite common, this does not mean that the job is easy. Roofs must be resilient against sun damage, rain, snow, and even events like hail. As such, roofing materials are harder to cut through and work with.
Roofing vents are often out of sight and mind, but this only applies when there isn’t a rooftop terrace on the building in question. When on the terrace, the rooftop vent will be in full view and they are often not very aesthetically pleasing.
Venting Through the Soffit
Advantages
The soffit is an extension of the roof, but separate at the same time. It’s the underside of the eaves, which means that you don’t have to worry about leaks in your home when you make a hole in the soffit to accommodate the bathroom fan.
In addition, the soffit is not exposed to direct or running rainwater and snow, which means that these kinds of leaks from the fan are not going to be a problem.
The wind is not likely to blow against the vents and counteract the outward flow of exhausted bathroom air, which would reduce the efficiency of the system.
You are also less likely to feel a cold draft coming in through a faulty backdraft damper if the fan vents through the soffit.
Disadvantages
Soffit bathroom fan vents can interfere with attic vents, which are often located in or near the soffits.
Firstly, bathroom fans are not allowed to terminate within 3′ of an attic vent, so you would have to move the attic vent, remove it, or install them illegally next to each other.
Moving an attic vent can be a hassle and result in less effective attic ventilation. Removing it entirely can cause insufficient attic ventilation.
When attic ventilation is ineffective or insufficient, you end up with an overly hot house, rodent and insect infestations, and even ice damming, which is when heat in your attic melts the ice on the roof and refreezes it at the edges. This can damage the whole roof system.
Venting sideways and then down through the soffit goes against the natural movement of hot air, which makes the whole system less efficient.
The backdraft damper helps to prevent air from flowing back into the duct, but it can still be problematic, particularly if the damper fails in any way.
In addition, the warm, moist air will still rise after exiting the vent and can linger under the soffit and cause moisture damage to your home.
Never Vent Into the Soffit
While you can definitely vent your bathroom exhaust fan through the soffit, you cannot vent it into the soffit.
Venting the fan into the soffit does not count as venting it outside, so this method contravenes the regulations set out in the building codes.
It means that all the moist and hot air that you are trying to get out of the bathroom simply gets deposited into a different part of your home, where it can still cause damage.
Better to Vent Through the Roof
Weighing the pros and cons of each method, the roof seems like the most ideal option.
There are, however, some exceptions to this.
Exceptions
If you have a low-pitched or flat roof, your bathroom fan leaking will be a big problem that venting through the soffit can fix.
If venting the bathroom exhaust through the soffit is a shorter route than venting through the roof, then the efficiency of the shortest ducting system can counteract any lack of efficiency of venting through the soffit.
Another possible option is to vent the fan through the side of the house.
Sources
https://longhomeproducts.com/blog/roof-ventilation-important-home/