We're going to move our washer/dryer to the garage (the front loader needs to sit on concrete to keep it from shaking our house to the ground).

I'll need to add a washer drain to the garage for the washer. Because this will need a p-trap, my understanding is that it also needs to be vented.

I could go straight up into the attic then through the roof, but my question is: do I need to actually go through the roof? Could I instead have it go into the attic then 90 degree it out to the back, second floor wall? I can't find any particular code rules on if it has to penetrate the roof or not. This is a septic system, if that matters.

The reason for trying to avoid the roof is that I'd prefer to not climb up onto the roof...it's about 45 degrees and in the PNW so perpetually wet and mossy.


2 Answers 2


No problem, as long as the vent meets the criteria listed below.

  • Not directly below a door, openable window, or other air intake opening (of this or any other building).
  • Not within 10 feet horizontally of the above mentioned openings, unless it's 3 feet above them.
  • Not less than 10 feet from the property line.
  • Not less than 10 feet above the ground.
  • Not under the soffit, if soffit vents are used (Covered by point 1 in my opinion).
  • Must be protected from birds and/or rodents blocking it.

International Plumbing Code 2012

Chapter 9 Vents

Section 903 Vent Terminals

903.5 Location of vent terminal.
An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet (3048 mm) horizontally of such an opening unless it is 3 feet (914 mm) or more above the top of such opening.

903.6 Extension through the wall.
Vent terminals extending through the wall shall terminate at a point not less than 10 feet (3048 mm) from a lot line and not less than 10 feet (3048 mm) above average ground level. Vent terminals shall not terminate under the overhang of a structure with soffit vents. Side wall vent terminals shall be protected to prevent birds or rodents from entering or blocking the vent opening.

And don't forget, if required you have to protect any extensions from freezing.

903.7 Extension outside a structure.
In climates where the 97.5-percent value for outside design temperature is less than 0°F (-18°C), vent pipes installed on the exterior of the structure shall be protected against freezing by insulation, heat or both.

  • 2
    I'm only speculating, but I would say because the vent is full of moist air. So you don't want the moisture condensing and freezing on the pipe wall, as this could lead to a blockage.
    – Tester101
    Commented Jan 29, 2015 at 17:56
  • 1
    This document lists the winter design temperature for some areas.
    – Tester101
    Commented Jan 29, 2015 at 18:00
  • 2
    Make sure when venting out you always have some sort of up pitch to the line.
    – DMoore
    Commented Jan 29, 2015 at 19:38
  • 2
    @DA01 Frost blockage from moist air is the concern. Good practice in cold climates is to increase the size of the vent when it hits the cold, as well as insulating it - that means a lot more frost has to form before it can block up.
    – Ecnerwal
    Commented Jan 30, 2015 at 14:58
  • 1
    The reason for the increase of size going through the roof is for frost collecting on the inside of the pipe thus reducing the opening.
    – Gary
    Commented Apr 23, 2017 at 15:04

Or, don't vent externally at all. In many jurisdictions you have the option of an AAV - Air Admittance Valve, readily installed in a wall box behind the washer. An AAV involves a gravity seal that opens just when needed to let fresh air into the plumbing pipe.

IPS Model 20381

Just makes sure what you get is a real AAV, not just a cheap $3 check valve. They're different. And keep in mind you may need to replace this unit in 20-30 years.

Look for units certified to NSF/ANSI Standard 14 and ASSE Standards 1051 and 1050. AAVs are not accepted everywhere, but they are approved for use under the International Plumbing Code (IPC), Section 917 and IRC, Section P3114.

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