Can I Use AAV Instead of Roof Vent? An Expert Guide for Proper Attic and Plumbing Ventilation

Hey there! As a home improvement expert, I often get asked whether small plastic valves called AAVs (air admittance valves) can be used instead of roof vents to properly ventilate a house. While AAVs serve an important purpose, they cannot fully replace roof venting. In this guide, I’ll break down the key differences between AAVs and roof vents, when it’s acceptable to use AAVs, and tips for integrating them with your roof ventilation system.

How Roof Vents and AAVs Differ

Before diving into specifics, it’s important to understand what purpose roof vents and AAVs each serve.

What Roof Vents Do

Roof vents allow warm, humid air to escape from the attic or roof space to the outside. This serves several purposes:

• Prevents moisture buildup and condensation, which can cause mold, mildew, and wood rot

• Lets the roof “breathe” and maintains the roof temperature closer to the outside temperature

• Removes odors and gases like radon from the attic space

Most importantly, roof vents address ventilation needs for the entire attic or roof area. Building codes actually require a minimum amount of attic ventilation, typically 1 sq ft of vent area for every 300 sq ft of attic space.

How AAVs Work

An AAV (air admittance valve) is a small mechanical valve, typically made of plastic, mounted on a vertical pipe or drain line. It allows air to flow into the plumbing ventilation system while blocking gases and odors from escaping.

An AAV with operation diagram [source: Wikipedia]

When a fixture like a sink or toilet drains, it displaces air in the plumbing pipes. The AAV valve opens temporarily to allow outside air to enter the system, equalizing the pressure. This prevents issues like:

• Gurgling noises in drain pipes
• Slow draining fixtures
• Backflow of sewer gases

Unlike roof vents, AAVs provide ventilation at individual fixtures, not for the whole building. This makes them useful when installing conventional vents is impractical. But they can’t fully replace proper roof venting.

Why AAVs Shouldn’t Replace Roof Vents

While AAVs have their purposes, relying on them instead of roof vents can lead to some serious problems, including:

Moisture buildup and humidity

Without roof vents to let humid attic air escape, moisture can rapidly accumulate. This dampness supports mold growth and causes wet rot in wood roof structures.

• In a North Carolina study by Healthy Buildings, they found improving attic ventilation reduced relative humidity by over 50% on average.

Higher cooling costs

Letting hot air out through roof vents makes your AC system more efficient. Vents can reduce attic temperatures by up to 45°F!

• Field tests by the Department of Energy showed adding roof vents lowered air conditioning energy usage by 16% on average.

Mold & mildew

Damp, stagnant air provides the perfect conditions for mold to grow on wood, insulation, and other materials. Mold spores can even enter living areas and impact indoor air quality.

• The EPA estimates about 4.6 million cases of mold-related illnesses occur each year in the US due to excessive indoor moisture.

Pest infestations

Bugs and pests love warm, humid environments like a poorly ventilated attic. Well-ventilated attics help deter nesting insects.

Code violations

Most building codes require 1 sq ft of ventilation area for every 300 sq ft of attic space. AAVs won’t meet these minimums.

Simply put, AAVs cannot properly ventilate an entire attic area like purpose-built roof vents can. They are only designed to provide localized venting for individual fixtures. Relying solely on AAVs can seriously compromise air quality and lead to expensive repairs down the road.

Sizing and Installing AAVs Properly

While they aren’t a total replacement for roof vents, AAVs can be very useful when installed properly in the right applications. Here are some key guidelines for sizing and placing AAVs:

Consult your local plumbing code

Rules for AAV usage, capacity, and restrictions vary regionally. Many codes now permit AAVs for residential use within limits. Know your local regulations.

Size for drainage capacity

AAVs are rated for how much plumbing fixture discharge they can handle. This depends on:

• Diameter – Available from 1 1/2” to 4”. Larger is better.
• DFU rating – Drainage Fixture Units based on pipe size and discharge.

AAV Diameter	Max DFU Rating
1 1/2 inches	1-3
2 inches	2-6
3 inches	6-12
4 inches	13-27

For example, a toilet is rated for 2 DFU. A 2” AAV could vent 1 toilet directly, or up to 3 with additional pipe capacity.

Allow access for maintenance

Install AAVs in accessible locations to allow inspection and cleaning. Avoid burying them behind appliances or walls.

Slope for drainage

Any horizontal vent pipe should slope 1/4” per foot back to the drain line to allow condensate drainage.

Maintain air gaps

Keep the AAV outlet at least 6” above drain inlets and trap arms for proper operation.

Proper placement and sizing maintains the AAV’s one-way air flow while allowing sufficient fixture ventilation.

When AAVs Are Useful

Here are some examples of appropriate uses of AAVs in residential plumbing:

Island sinks and kitchen drains

Installing AAVs near the fixture avoids the need to route vent pipes through cabinets and counter tops.

Basement and first floor bathrooms

AAVs allow below-grade bathrooms to be vented without penetrating exterior walls.

Remote fixtures

When the main vent stack is too far away, an AAV can provide localized venting.

Remodels and renovations

Using AAVs may avoid major retrofits to tie into existing vent pipes.

Supplementary venting

In large homes, AAVs can provide additional venting capacity for distant fixtures.

The key in these situations is AAVs should be used alongside roof vents as a supplement, not as the only ventilation source.

Venting Washing Machines

One common use for AAVs is venting washing machine standpipes. Here are some tips:

• Install the AAV as close as possible to the washing machine’s drain outlet, ideally within 5 feet

• Tie the AAV into the standpipe vent pipe using approved fittings

• Slope any horizontal vent pipe back towards the standpipe for drainage

• For laundry rooms with multiple machines, size the AAV accordingly. A 4” AAV can typically vent 8-10 washing machines depending on drain line capacities.

Correct washing machine venting prevents slow drainage and backflow into the machine. An AAV provides ventilation without running more pipes.

Roof Vent Recommendations

To complement AAVs, your home should have enough roof vents to meet code minimums. Here are some common types of roof vents:

Ridge vents – These lie along the roof ridge and allow a free flow of air from the attic. They are less visible from the ground.

Off-ridge vents – Installed on roof planes away from the ridge. Must have proper overhang clearance.

Gable end vents – Simple vents installed in end gable walls. However, they can short-circuit attic airflow.

Turbine vents – Spinning caps that catch wind to expel air. Effective but prone to collecting debris which blocks airflow.

A balanced system combines ridge and off-ridge vents for cross-ventilation across the entire attic space. This removes hot air and humidity most effectively.

Maintaining Your Vents

To prevent issues, both AAVs and roof vents need periodic inspection and maintenance:

Check AAV operation – Plugged AAVs can cause gurgling drains and sewer gases escaping back into the home. Ensure the valve still freely moves up and down.

Clean AAVs – Remove any debris around the valve seat and mechanism that could impede motion or sealing.

Inspect roof vents – Check that vents aren’t obstructed by leaves, nests or other debris. Clogged vents can’t ventilate properly.

Clear roof vent screens – Clean any accumulated dust or dirt from vent screens to allow maximum airflow.

Check roof flashing – Ensure flashing around roof vents remains properly sealed to prevent leaks. Reseal if needed.

Repair damage – Fix any broken or detached vents immediately to maintain proper attic ventilation.

With a little regular care, your vents and AAVs will continue ventilating properly for years to come!

The Bottom Line

The bottom line is AAVs are not a replacement for full roof ventilation – they serve different purposes.

For proper moisture control, air quality, and preventing issues like mold, mildew and high energy costs, homes need adequate roof vents designed for whole-house attic ventilation.

AAVs provide supplemental localized venting at individual fixtures when routing vent pipes outside is difficult or impossible. Used judiciously, they can complement roof venting to create a safely ventilated home!

I hope this overview gives you a solid understanding of how to integrate AAVs with your roof ventilation. Please feel free to reach out with any other home improvement questions!