Backflow prevention for dishwashers

I imagine, optimally, an air-admittance valve would be in order.
But what about dishwashers w/o AAV’s?

Is an upward slope from the dishwasher and then a slope downward
toward the garbage disposal (or waste drain) acceptable?

I have seen some that have virtually completely level d/w drain slope,
and previous owners have complained about dirty water being left in the bottom of the dishwasher after a cycle.
I certainly write those up.

But back to ?: Is upward slope from d/w and then downward slope toward waste drain good enough for anti-backflow?

Typically, yes. It’s called a high loop.

That’s what I figured.
Now I know what it’s called !
Thanks again,

I assume you’re actually referring to an air-gap rather than an AAV.

AAV’s are a vent system which has nothing to do with back-flow prevention. An air-gap device is used in dishwasher drain lines to prevent back-flow.

High-loops are allowed by many model codes, but not here in CA.

As with everything, though, final say-so is up to the local AHJ. I have a gazillion bazillion brand new multi-million dollar homes in brand new subdivisions with dishwashers on kitchen islands where the local AHJ here allows high loops.

I see these often too. But the code is very clear about this, and it should be mentioned in your report.

Here’s how I state it. . .

The dishwasher is functional but discharges without an air-gap fitting, which is mandated by California Building Standards. The absence of the air-gap fitting may also create a drainage problem and a health hazard.

and here’s the code. . .

CPC 807.4 No domestic dishwashing machine shall be directly connected to a drainage system or food waste disposer without the use of an approved dishwasher airgap fitting on the discharge side of the dishwashing machine.

I mention it, but I don’t use code references or “mandates” like you do.

And it’s still up to the local AHJ to interpret:

Not much left to the imagination here, it’s pretty cut and dry.

Now, obviously, a variance can be obtained to circumvent almost any code requirement, but I am certainly not going to just “assume” this has been done. The homeowner can do the work to verify this.

Sometimes the AHJ does probably use his imagination for purposes of interpretation. :slight_smile:

Or they can hire me as a consultant to verify it at $100 per hour, which several have done. Now that I know what subdivisions are involved, I can simply put the information in my report, and if they still want me to verify current interpretations, I do that.

:wink: If it does not have an AAV , The discharge hose must be atleast 32 inches long and extend above the level of the dishwasher per the IRC

An AAV is a vent system. An AAV is not the same as an air-gap or high-loop, and it performs a completely different function.