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Is venting fart fans into the attic within code?


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I found this on an inspection last week. This is a flex hose coming from the master bathroom fart fan. I have tried to find out via the IRC 2003 if this is legal. Can anyone confirm? This is venting directly into the attic over the garage portion of the home. I was taught in inspection training school that nothing should vent into the attic, but I do not know if that is code or just a recommendation.



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From the 03' IRC

303.3 Bathrooms.

Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.279 m2), one-half of which must be openable.

Exception: The glazed areas shall not be required where artificial light and a mechanical ventilation system are provided. The minimum ventilation rates shall be 50 cfm (23.6 L/s) for intermittent ventilation or 20 cfm (9.4 L/s) for continuous ventilation. Ventilation air from the space shall be exhausted directly to the outside.

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Good news bad news.

The 2000 IRC does not prohibit an exhaust fan for a bathroom from venting in the attic.

I am not disputing Chris's post however some AHJ's have said that a vented attic is outside of the living space therefore outside.

attached is the code, and lots of it. Dryer vents and range hoods are prohibited but exhaust fans fall under section 16 and are not addressed.

Check with the manufacture of the fan, if it is designed to vent outdoors they would need to correct it.

Everything below this is from the 2000 IRC, if you are looking for commentary you will not find any more in this post.

2003 IRC





M1501.1 General.

Dryer exhaust systems shall be independent of all other systems, shall convey the moisture to the outdoors and shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer's installation instructions. Screens shall not be installed at the duct termination. Exhaust ducts shall not be connected with sheet-metal screws or fastening means which extend into the duct. Exhaust ducts shall be equipped with a backdraft damper. Exhaust ducts shall be constructed of minimum 0.016-inch-thick (0.406 mm) rigid metal ducts, having smooth interior surfaces with joints running in the direction of air flow.

Flexible transition ducts used to connect the dryer to the exhaust duct system shall be limited to single lengths, not to exceed 8 feet (2438 mm) in length and shall be listed and labeled in accordance with UL 2158A. Transition ducts shall not be concealed within construction.

Exception: This section shall not apply to listed and labeled condensing (ductless) clothes dryers.

M1501.2 Exhaust duct size.

The diameter of the exhaust duct shall be as required by the clothes dryer's listing and the manufacturer's installation instructions.

M1501.3 Length limitation.

The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7620 mm) from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.


1. Where a clothes dryer booster fan is installed and listed and labeled for the application, the maximum length of the exhaust duct, including any transition duct, shall be permitted to be in accordance with the booster fan manufacturer's installation instructions. Where a clothes dryer booster fan is installed and not readily accessible from the room in which the dryer is located, a permanent identifying label shall be placed adjacent to where the exhaust duct enters the wall. The label shall bear the words "This dryer exhaust system is equipped with a remotely located booster fan."

2. Where the make and model of the clothes dryer to be installed is known and the manufacturer's installation instructions for such dryer are provided to the building official, the maximum length of the exhaust duct, including any transition duct, shall be permitted to be in accordance with the dryer manufacturer's installation instructions.



M1502.1 General.

Range hoods shall discharge to the outdoors through a single-wall duct. The duct serving the hood shall have a smooth interior surface, shall be air tight and shall be equipped with a backdraft damper. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.

Exception: Where installed in accordance with the manufacturer's installation instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.



M1505.1 Ducts.

Where exhaust duct construction is not specified in this chapter, such construction shall comply with Chapter 16.



M1506.1 General.

Where toilet rooms and bathrooms are mechanically ventilated, the ventilation equipment shall be installed in accordance with this section.

M1506.2 Recirculation of air.

Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit.



M1601.1 Duct design.

Duct systems serving heating, cooling and ventilation equipment shall be fabricated in accordance with the provisions of this section and ACCA Manual D or other approved methods.

M1601.3 Installation.

Duct installation shall comply with Sections M1601.3.1 through M1601.3.6.

M1601.3.1 Joints and seams.

Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing or other approved closure systems. Closure systems used with rigid fibrous glass ducts shall comply with UL 181A and shall be marked ia181A-Pla for pressure-sensitive tape, ia181A-Mli for mastic or ir181A-Hli for heat-sensitive tape. Closure systems used with flexible air ducts and flexible air connectors shall comply with UL 181B and shall be marked ia181B-FXlv for pressure-sensitive tape or ia181B-Mls for mastic. Duct connections to flanges of air distribution system equipment or sheet metal fittings shall be mechanically fastened. Crimp joints for round ducts shall have a contact lap of at least 1.5 inches (38 mm) and shall be mechanically fastened by means of at least three sheet metal screws or rivets equally spaced around the joint.

M1601.3.2 Support.

Metal ducts shall be supported by 0.5-inch (12.7 mm) wide 18-gage metal straps or 12-gage galvanized wire at intervals not exceeding 10 feet (3048 mm) or other approved means. Nonmetallic ducts shall be supported in accordance with the manufacturer's installation instructions.

M1601.3.3 Fireblocking.

Duct installations shall be fireblocked in accordance with Section R602.8.

M1601.3.4 Duct insulation.

Duct insulation shall be installed in accordance with the following requirements:

1. A vapor retarder having a maximum permeance of 0.05 perm [(2.87 ng/(s · m2Pa)] in accordance with ASTM E 96, or aluminum foil with a minimum thickness of 2 mils (0.051 mm), shall be installed on the exterior of insulation on cooling supply ducts that pass through nonconditioned spaces conducive to condensation.

2. Exterior duct systems shall be protected against the elements.

3. Duct coverings shall not penetrate a fireblocked wall or floor.

M1601.3.5 Factory-made air ducts.

Factory-made air ducts shall not be installed in or on the ground, in tile or metal pipe, or within masonry or concrete.

M1601.3.6 Duct separation.

Ducts shall be installed with at least 4 inches (102 mm) separation from earth except where they meet the requirements of Section M1601.1.2.

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Just so we don't get into a argument about this. I write it up as being wrong also, however I had a Senior Building Official tell me I was wrong and quoted the reference that I posted. I showed him the code that Chris posted and he said the attic is considered outside.

Now I try to clarify that it may be OK according to the code officials interpretation

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Venting Bathroom exhaust fans into the attic space will cause damage to the attic structure.

It has been known to collapse ceilings and cause $$$ in damages.

If you want we can have the long conversation but venting ANYTHING into attic spaces is WRONG.

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Some of this is regional in my opinion. If you live in the steamy South and you have adequate attic ventilation (just adequate), venting bath exaust fans into the attic is harmless. I've never seen one that was actually vented to the exterior. In other parts of the country I'm sure it would be a problem. Given our daily humidity levels, the amount of moisture vented into an attic after a shower is akin to taking a whiz in a lake...no harm done.

I see it on every inspection, and I don't write it up. If I lived where Rob lives, I'd write it up every time.

Brian G.

Wild-Eyed Rougue Inspector [:-masked]

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Hi Jim:

It was either here or the ASHI site. They ran the duct to the soffit vent and the roof sheathing had quite a bit of mold on it. The discussion was centered around soffit vents being intakes and not an exhaust vent. I think we went on to discuss if it was ok to terminate the duct at a ridge vent or other high exhaust opening.

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A slight twist on this thread. Here in S. Florida if a gas water heater is installed in a confined space combustion air must be provided by way of two vents. One at the top of a door and one at the bottom. The size of the vents, according to the code, may be reduced and/or eliminated if an outside source of combustion air is provided. Most of the AHJs, here, consider the attic to be outside air and allow a 4"-6" sleeve to communicate between the attic and confined space. I don't agree but I'm not the AHJ. Actually in my own house I am, at least in my mind.


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Norms comment regarding high/low air intakes is the same as Chicago; the powers that be want to see a convective loop of intake air. I believe it is a component of the "new" NFGC 2002 edition. (National Fuel Gas Code)

Specifically, the NFGC requires that "two permanent openings shall communicate directly, or by ducts, w/ the outdoors or spaces that freely communicate w/ the outdoors."

In a lighter vein......

I am kind of a nature freak, & I communicate directly w/ the outdoors through 2 of my permanent openings; I am offering myself as combustion air vent source.

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Originally posted by Jim Morrison

Do I place my HI license in jeopardy when I fart directly into an attic during an inspection?

No, but you may not get a referral on that one.

What about when I'm at home?

A man's home is his castle, period. Let 'er rip.

Out of state?

You'll have to check with the local AHJ on that. Dan?

Or should I start another thread?

Nah, I think I've covered it.

Brian G.

Flatus Protocol Expert [:-crazy]

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hi Jimmy,

as you opperate in a State that has seen fit to regulate every other area of business, my recomendation would be to put this issue in front of the Massachusetts State Licensing Board, you can't be too carefull. [:-bonc01]

as my learned friend Brian G pointed out "every mans home is his castle" so you should be safe there (god help the rest of the family though !!) [:-sick]

However as to the out of state issue that you raised, my best recomendation is that if you suffer from terminal flatulence due to a diet soley made up of a mix of Clam Chowda, Sam Adams & Boston baked beans. I think you should concider moving your business over the boarder to New Hampshire, "The Fart Free or Die" state [:-eyebrows]

I hope you find this usefull [:-jester]



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  • 2 weeks later...

Its a regional issue. The code book says one thing the local code people say something else.

When I'm in Dallas, TX they go to the outside.

In Kansas or Missouri "NO PLACE" that I've ever inspected (Kansas City, Wichita, Columbia, Lake Ozarks, Lawrence, St. Louis, etc) has run them outside and since 1988 I've only seen 2 times where its created a problem and in both cases the attic had no ventilation at all.

Our code authorities have determined that if the attic is well ventilated then the attic is outside the living quarters and thats where they go to.

Now for your general info, I'm told that because of mold issues Johnson County, Kansas

will start requiring them to REALLY go OUTSIDE later this year.

Dan Bowers (Kansas City)

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  • 9 months later...

Seriously though, I must go with Brian G. on this one folks. "Regional" Reason??? I don't need a blanket answer for looking both ways when I cross a street. Busy street, I pay more attention. Just like we should pay attention to where we live and work as far as attic ventalation and venting into them. Causing visible suspect mold in an attic crawl space?!? Don't vent there anymore. Dry climate?!? don't worry about it. It is all realative folks. Thanks for your time.

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Around here they are usually run into the soffitts. I believe that this is due to a lack of education "we always do it that way). I insist on them being thru an exterior wall with a cap hood. It does not cost me anything and if it cost $50, who cares. There is no downside to venting them to the exterior, in my opinion this is a no brainer.


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  • 8 months later...

I need some help! I too live in Gilbert, AZ and have recently had my home inspected. I was told that my range hood vent terminated in the attic and needs to be routed to the roof. My question is this, if my home was built in 1984 does it fall under current code requirements? If so, is it the home owners assosiations responsibility to fix? Any assistance on this would be greatly appreciated.

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This is exactly why I avoid code references. I would simplify the argument by providing my pics of bathroom vents that terminate in attic spaces which just happen to be surrouned by mold. My clients don't care about code at that point and the AHJ can quote code till he's blue in the face- my butt is covered.

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