Venting Bathroom Fan into Attic: Problems and Alternatives

Bathroom ventilation fans are the best way to remove moisture from bathrooms, but that humid air needs somewhere to go. Venting bathroom fans into an attic is one of the first options homeowners turn to, as it may seem like the simplest approach.

That couldn’t be further from the truth, however, which is why you should never vent a bathroom fan into an attic space.  

Many solutions are more suitable for these installations, whether the bathroom is on the first floor of a two-story home or a rarely used upstairs bathroom.

Can I Vent a Bathroom Fan Into an Attic?

The simple answer to whether you can vent a bathroom fan into an attic is yes, but you’ll risk damage to your home if you do so.

Do not vent anything with moisture into an attic. It’s a code violation and can cause significant damage to your home.

This will cause mold, mildew, and potentially rot depending on the conditions present in the attic and the exhaust going into it. Attics are not “temperature-controlled,” so the conditions in these areas fluctuate throughout the year.

When warm or humid air mixes with cold air in a closed environment, it will create condensation. Condensation can lead to ceiling damage when water drips from the rafters in a worst-case scenario or an expensive case of mold removal.

Bathroom exhaust fan venting into an attic is also considered a code violation if the home is in the United States. Bathrooms aren’t required to have an exhaust fan, but they must be ventilated outside when they do.

Where Can a Bathroom Exhaust Fan Be Vented?

If you are considering installing a bathroom exhaust fan and aren’t sure where to vent it, you’ll be thrilled to know several alternatives are available.

These methods are all approved for building codes in the United States, although it’s still a good idea to check on the building code for your country or region beforehand.

1. Through-Wall Ventilation

This is the most popular method used in bathroom fan ventilation as it gives professionals more options to route ductwork from the bathroom.

The “through-wall” method for exhaust fan ventilation refers to any exhaust vent that’s run from the bathroom fan through the wall of your home.

That could be up and over the ceiling to a vent directly outside the bathroom, which is the shortest approach.

If the bathroom has several rooms between it in an exterior wall, the ducting can take a variety of paths as well. These vents terminate outdoors on the side of a home and must be covered by a vent with flappers or a hood.

These features prevent animals from getting inside the ductwork while offering protection from the weather. These vents have the potential to leak when not sealed properly, but this is the method found in most residential homes regardless of age.

2. Roof Venting

The other option for venting a bathroom fan is to go through the roof – not the wall. It’s the only way to go through an attic area safely, although ductwork will still need to be insulated to prevent condensation in most cases.

Roof venting terminates on the roof of a home where it’s covered by a hood. Roof vents are bigger with a larger vent hood and more weatherproof than through-wall vents, given their exposure to the elements. 

Pets and bird nests can be an issue, so you’ll want to pay attention to the size of the grates on any type of roof vent. 

The design of roof vents allows them to expel more warm air and provides plenty of options from an installation standpoint. They are not without fault, however.

Unless you’ve handled roofing and are comfortable with heights, you’ll want a professional to install any bathroom fan vent covers on a roof. They can ensure any ducts that run through an attic are safe and keep the vent on top of your home from leaking.

3. Low-Profile Wall Fans

This option is the best choice for homeowners that want a bathroom fan but don’t already have one installed in the ceiling. It’s still suitable for existing overhead fans, although that system will need to be removed and the ceiling patched.

Bathroom wall fans are thinner than a ceiling-mounted fan, and they have a more streamlined design. This allows them to slide seamlessly between studs in a bathroom wall and provides another advantage.

You can take this type of bathroom vent directly through the wall outdoors, so it’s technically a through-wall installation. It decreases the amount of bathroom vent required but may need an electrician to wire the new fan into your home’s electrical system.

As with roof and ceiling-through-wall installations, the exhaust vent will need protection from insects, animals, and the elements.

4. Soffit Vent

Venting bathroom exhaust fans into soffit vents is another method that can violate building codes in your region. It’s something that’s done, although it can be far more trouble than it’s worth when you consider the potential drawbacks.

Soffit vents are the smallest type of bathroom vent and discreet compared to roof or wall vents. Most people don’t even notice a soffit vent for a mechanical exhaust system unless they look at the underside of a roof’s overhang. 

While you’ll still need ductwork and a soffit vent, it may be the cheapest type of installation, depending on the layout of your home.

Unfortunately, it’s not a good idea. The soffit itself provides airflow and keeps animals out of the roof area of a home. Disrupting the pattern of airflow in these spaces can have adverse effects, and the rafters could become damaged if moisture seeps in.

If you are considering venting a bathroom exhaust fan through the soffit vent, check on building codes in your area and consider a professional for the job.

How Much Does It Cost To Install an Exhaust Vent?

Once you understand the options available and why you should never vent bathroom exhaust into an attic, it’s time to consider the installation process itself.

The parts required to take exhaust from a fan to the outdoors is minimal compared to the price of the fan with most installations.

Exhaust fans can run anywhere from $30 to around $60 if you want one without a light like this well-built and relatively quiet system Tech Drive.

While not very stylish compared to the colorful ChromaComfort from Broan NuTone, fans in the budget to mid-range class get the job done.

A bathroom vent is cheaper than bathroom exhaust fans, whether installed on a roof or through the side of a bathroom wall. Roof vent kits caps or hoods range from $25 to $60 with a built-in damper and pest guard. 

You may also need shingles for a roof, along with sealant and flashing to keep things watertight for this type of bathroom vent.

Through-wall bathroom vents come in more styles, including round stainless steel vents. Parts are difficult to price as every installation will be slightly different, but there are a number of wall ducting kits that have almost everything you’ll need.

On average, you can expect to spend between $100 to $300 to vent a bathroom fan through a wall or roof if you plan to do it yourself.

The cost can rise significantly for professional installations once they venture out of the bathroom and onto the roof. 

It’s not uncommon for a handyman to charge $100 to run a vent through a wall, but installing bathroom vents on a roof, flashing it in, and ensuring it’s sealed properly could be up to $500 or more.

Location plays a large part in pricing, along with access to the bathroom fan and where it needs venting.

The advantage of going to a reputable professional is that you’ll get a guarantee on the work, and they can supply all the parts required for the job.

The Bottom Line

Venting bathroom fans into attics is a bad idea, and now you understand why it’s never something a contractor would approve of, and it’s not a method that’s up to code.

It will cause issues with the structure of your home and is a waste of time and money when there are more suitable alternatives available.