NC plumbing code for washer machine venting

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NC remodels

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North Carolina
Hello, New to the forum! I renovating my 100 year home and have a new laundry and bathroom that I had plumbed by a company. Below is the diagram. I'm hearing from lots of folks that the washer machine (WM) should not be vented this way. They are basically using a 160 DFU AAV to vent the washer, laundry sink, tub and I think the toilet. The washer ties into the 3" horizontal by a 3" Y connection about 6" downstream from 2" Y that connects the sink and tub/shower. The toilet is about 10 developed feet from the existing 3" stack that has a 3" thru the roof vent. There is also about 2.5" of fall in the 3" horizontal from the washer Y to the toilet connection T. The other 3" horizontal after the toilet has about 3"/foot fall before it goes vertical and ties into the existing 3" sewer. Below are my question..

-Will the WM venting give me problems? The inspector says its ok, the AAV manufacturer says its ok and there are more than enough DFU's on the AAV. Both 2" horizontals coming from the tub and laundry sink are about 2' in length. Will I have problems with siphonage and gurgling of the traps up stream? I could easily take the laundry off the AAV and run a dedicated vertical stack and tie into the existing. The company says this it not necessary and wants to charge $400 extra. Is this advisable even though the WM drain will still tie into the 3" at the same location below?
-Is the toilet venting by way of the existing stack 10' away or is it also using the AAV on the laundry sink which is about 8' away. If it is venting by the AAV will this wet venting situation be problematic because the washer is draining on that same line? If I do add the dedicated vertical stack for the Washer will the toilet then be wet venting through the washer machine drain and if so is that OK?
-Is the fall in the 3" horizontals too much? I know there is a minimum of 1/4" but the plumber says there is no maximum. I believe there actually is a max if this is a combo waste/vent situation though...


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