Venting a Bathroom Fan Into An Attic (My Detailed Guide)

Should a bathroom fan hose be vented into an attic? If so, how is it done?

During my home inspections, I have come across many bathroom vents incorrectly installed into attics leading to mold and moisture damage.

In this article, you will learn…

  • Why you should never terminate a bathroom vent inside an attic
  • How to properly vent a bathroom fan duct to the outside through an attic
  • The real reason you should insulate a bathroom vent pipe contained in an attic

Can I Vent a Bathroom Fan Into My Attic?

No, you should not vent a bathroom fan directly into an attic. However, you can vent a bathroom fan through an attic while it terminates on the roof or gable end.

It seems like such an easy solution, just leave a bathroom vent hose in an attic. It’s all outdoor air anyways, right?

Let me tell you: improperly ending a bathroom vent inside an attic can lead to “unintended consequences” — and builders have stopped this bad practice many years ago. Prior to the 90’s, builders commonly vented bathrooms into attics.

On my home inspections, it is still a common sight for me to see bathroom vents going directly into the attic — spewing moisture.

The problem with this approach is that all of the moisture in the air goes onto the wood sheathing, insulation, wood rafters, and wood ceiling joists — which can lead to mold growth and rot. Especially during cold weather months, the excess moisture from a bathroom vent can build up frost on the underside of the roof sheathing, and eventually this ice will melt and leak onto the insulation and drywall ceiling.

Read Also: What Are The Best Bathroom Fans With Humidity Sensors?

How Do I Properly Vent A Bathroom Fan Into An Attic?

The correct way to vent a bathroom fan through an attic is to terminate the vent either to the roof or to the gable wall.

Either way, the vent will have to go directly to the outside, and installed with a vent hood cover. The vent hood will have a little flap that opens when air is blowing through the vent, but at other times it will remain closed.

The flap will help prevent outdoor air from going into the home when the bathroom vent is not on. The flap and screen will also prevent birds from nesting in the bathroom vent which is extremely common.

A bird’s nest in a bathroom vent will greatly reduce or eliminate the effectiveness of a bathroom exhaust fan. It’s also important to note that if you install a roof vent cover for a clothes dryer, you must remove the metal screen because it will catch lint and may turn into a fire hazard.

Roof Vent Covers

It is also important to note that vent hood covers for the roof are a different and specialized type of cover. You can’t just take a normal hood cover and install it on the roof. The roof covers are made from metal, and are much more robust, and somewhat more expensive.

The Builder’s Best Roof Vent Cap is powder coated and galvanized—which is really important when it’s on the roof. It also comes with the required flapper, as well as pre-drilled holes for an easier installation.

You can view the latest price for the Builder’s Best galvanized steel roof cover here.

venting bathroom fan into attic

Read Also: How To Replace A Bathroom Fan Without Attic Access

How Much Will It Cost To Vent Through An Attic?

The cheapest part of installing a new bathroom vent will likely be the supplies. You can get a 25-foot insulated bathroom vent and the cover for around $70 total.

Most of the cost will be in the labor. Also, if you are venting up to the roof, then a roofer will be required which will cost more than if you are venting to a gable wall or soffit.

Installing a new vent through an attic is going to cost on the low end around $200 just for labor, and may be as much as $500 to $750 if it is a complicated vent that goes to the roof. 

What About Venting To The Soffit Vent In My Attic?

Even though it is not my preferred installation, it is possible to vent your bathroom fan directly to the soffit vent. In this way, you avoid messing with the roof and the associated leak risks.

The downside of soffit vent installations is that it may disrupts some of the air flow of the soffit venting. Soffit vents work because the warmer attic air (relative to outside) rises, and it creates a suction effect when working in tandem with the ridge vent.

In addition, the excess moisture may result in wood damage and mold growth.

However, if a homeowner really wants to terminate their vent at the soffit, I recommend using a specially made soffit vent cover.

These bathroom fan vent covers are designed to be installed on the soffit vent. The Dundas Jafine Soffit Vent Cover includes a spring-loaded damper (flap) with a flush mount style so it blends into your soffit vent.

I invite you to see the current price for the Dundas Jafine Soffit Cover right here.

venting a bathroom fan into attic (pic) (1)

Can I Vent My Bathroom Duct To The Ridge Vent?

Another very common thing I see during home inspections is that the bathroom vent is vented just below the ridge vent. This is probably a better thing than venting it to the soffit vent, but it can still cause problems.

venting bathroom fan into attic

When the air in the attic is warmer relative to the exterior, this rising attic air powers the natural soffit-ridge vent system. It creates suction effect and pulls in the cooler exterior air from the soffits as it rises through the ridge vent.

Also, the vent is always terminating a few inches BELOW the ridge vent, so when it is venting, all of the air is not going directly the outside. Much of the air is bouncing around the edge of the ridge vent, and the wood sheathing. So venting it to the ridge vent can still lead to mold growth and wood damage.

Read Also: What Are The Best Rated Ultra Quiet Bathroom Exhaust Fans?

How Do I Prevent Moisture When Venting a Bathroom Into An Attic?

When a bathroom vent is making a long horizontal run in an attic, there is always a risk of condensation or water droplets. I always recommend installing an insulated bathroom vent, which is a just a normal vent surrounded by fiberglass insulation.

This will greatly help reduce the potential of condensation forming which may lead to drywall damage or mold problems.

Condensation forms when two different temperatures meet — such as a cold drink on a very hot day — water droplets forms on the outside of the glass.

If you are sending warm interior air through the bathroom vent while attic is very cold, then water may form. In addition to insulating your bathroom vent, you want to avoid U-shaped bends in the vent, because this will allow condensation on the inside of the vent to drip towards the low point of the vent hose.

The Dundas Jafine Insulated Flex Duct is pre-wrapped in fiberglass insulation and includes an outer vapor barrier which helps prevent condensation problems. The Dundas Jafine is a 4-inch duct and 24-feet in length. View the latest price for the Dundas Jafine duct right here.

venting a bathroom fan into attic

Read Also: What Are The Best Bathroom Exhaust Fans With LED Lights?

The Truth About Attic Bathroom Venting

Venting a bath fan through an attic can be done, but it should terminate on the outside.

I would by lying if I told you that it will cause problems, it may be totally fine. In fact, I have seen numerous houses that haven’t yet had signs of mold with the bath fan venting incorrectly.

A Few Possible Issues

However, there are a few real potential downsides when a bathroom vent is improperly terminated inside an attic:

  • mold growth
  • wood rot and structural deterioration
  • moist bathroom air is sucked back into the home interior
  • excess moisture attracting rodents and pests 
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2 thoughts on “Venting a Bathroom Fan Into An Attic (My Detailed Guide)”

  1. My bathroom fan leaks on to the floor when ouside temperature is below freezing. Does not happen when very cold. This has been an issue since installed. I know it is condensation inside tube. Tube is insulated and about 12′ long goes vertical up at about 20 degrees through the attic and out the roof. What is my problem? Should tube have S, or P, or horizontal turns as it travel in attic

    • Ideally it shouldn’t have any bends, but definitely not an S type turn. Horizontal runs are okay but the turns should be as gentle as possible. It may be difficult to diagnose where the issue is. I would probably just replace the entire duct in the attic. There are pre-insulated ducts that you can buy, but most of them are flexible ducts with ridges which aren’t as good as rigid metal. You may also have poor insulation/ventilation in attic which can be related.

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Arie Van Tuijl

Arie Van Tuijl

I am a licensed home inspector in two U.S. states and the founder of Home Inspector Secrets. After performing hundreds of inspections, and seeing thousands of house defects, I realized people would love to have an online resource dedicated to home maintenance. I write detailed home guides and product reviews sprinkled with inspection tips. You can read my bio here.

About Home Inspector Secrets

Home Inspector Secrets is an online resource for owners, buyers, and sellers to understand all aspects of home maintenance. We have detailed home guides, product reviews, inspection advice, and much more.

Other Home Guides

Looking to learn more about home maintenance? Check out our other informative home product reviews and guides!