Backflow prevention for dishwashers

Specific Inspection Topics Plumbing Inspections
#1

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?

#2

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

#3

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

#4

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.

#5

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.

#6

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.

#7

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:

#8

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.

#9

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.

#10

: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

#11

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.