The International Residential Code (IRC) does not prohibit termination of a dryer exhaust duct through a soffit, but the code restrictions and installation problems make it more difficult than other termination locations. Here’s a list of the issues to contend with:

•• The termination must be at least 3-feet away from any openings into the building, which includes openable windows and doors (IRC M1502.3). The code formerly included “passive soffit vents” as building openings that also had to be at least 3-feet away from the duct termination, but that has since been removed. The termination must have a backdraft damper and no screen. Go to What are the code requirements for an outdoor dryer vent cover? to learn more.

•• Because the code always defers to manufacturer’s installation instructions, you need to verify that the dryer manufacturer does not prohibit soffit vent terminations (IRC M1502.3)

•• The flexible transition duct connected to the dryer is not allowed to penetrate a wall, floor, or ceiling (IRC M1502.4.3). The entire length of it must be exposed to view. So the section that runs through the wall and attic to the soffit must be smooth metal.

•• If the dryer is located in the middle of the house, the maximum length of a straight run of dryer duct is 35 feet, with a 5 foot deduction in length for each 90º bend and half that for 45º bends, based on using a 4-inch smooth metal vent, with no screws protruding into the air flow (IRC M1502.4.5.1). The deductions for bends could limit the run to 20 feet or less. See our article What is the maximum length for a clothes dryer vent? for more details. 

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Here’s links with answers to some of the questions we get asked most often about dryer venting:  

• Why does venting a clothes dryer into a garage, attic, or crawl space cause problems?

• Why is it bad to have a clothes dryer vent near an air conditioning condenser (outdoor unit)? 

• What are the code requirements for an outdoor dryer vent cover? 

• How do you inspect a dryer vent? 

• What is code for dryer vents? 

• Do home inspectors check the clothes dryer exhaust vent system?

• Can you vent a clothes dryer into the attic?

• What is code for dryer vent termination clearance? 

• Can a clothes dryer vent in a mobile/manufactured home terminate in the crawl space?

• How do I do a safety inspection of a dryer vent? 

• Does a home inspector check the clothes dryer?

• What is the average life expectancy of a clothes dryer?