I inspected a home, new construction. Ranch style with 2 bedrooms up, 2 baths up, kitchen up. 2 bedrooms down, 1 bath down and a kitchen down on the finish lower level.
In the attic I was able to see (1) vent stack (2 1/2") through the roof.
Construction is in a rural area, no codes, with septic system.
Builder completed the Plumbing!
My question is with all these fixtures, with the layout of the plumbing from one side of the home to the other, should there not be a waste stack and atleast 2 vents?
Did you see any auto-vents?
Fixtures should all back vent to the main vent line and exit the roof as a 3" vent. Would all drain to a 4" waste line. 
Robert,
First thanks for responding. No there were under sink vents visible.
Marcel,
Thank you for the reply. No 3" line out of roof.
I noticed that almost a hundred viewed my request for information, but only (2) members responded. I’m not sure if its because most were unsure and did not want to speculate or if it depended on what area of the country and did not want to speculate. For the Missouri members, most particular, those in the areas were there are no codes, it was explained to me by a master plumber that a single vent is used in alot of cases to vent the entire home. The toilets are the primary concern and the remaining fixtures are just re-vented to the single vent. It was said that this method is not the most desirable and can cause problems, but is common in rural areas.
Steve, in the absence of code you have two choices. Please the real estate salesman and look the other way since the lack of a standard is, in the minds of some, justification for creativity is the first choice. Your second choice is to explain to your client that the plumbing fails to meet the standards of what are considered to be standard building practices…and fully describe the difference between what was done and what the standard is. Do not use the word “code” and you cannot be credibly contradicted by anyone.