Vent Stack questions

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Rbt238

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(Residence in Florida, and before I call the local Bldg Inspection office and get the usual run around, I wanted to get some practical input from Pro Plumbers)
I plan to have a Metal Roof installed sometime next year and currently have a 3" stack on one part of my roof and a 2" stack on another area.
I want to eliminate as many roof protrusions as possible since I've heard of issues with how Metal Roofs are sometimes flashed around them.
I read that at least one vent is required by the International Residential Code (IRC P3114.7): “Within each plumbing system, not less than one stack vent or vent stack shall extend outdoors to the open air.”
Questions are,
(1) Can all the stacks be connected in attic to a single stack going out the roof?

(2) And if so is there a Diameter size requirement on the one stack?

(3) Or if I have one stack through the roof, can I put an Air Admittance Valve like the Oatey Sure-Vent apparatus on a Toilet stack?
 
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Terry

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Plumbing code expects to see the same area going through the roof, as out to the street on the sewer.
A three bath home can be done with 3", a four bath home has been bumped to 4".
With venting through the roof to handle positive and negative pressures, a lot of local codes will allow some fixtures to be vented with an AAV.

dwv_b2.jpg


Venting is allowed to be tied together in the attic.
 
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