Your inspector is correct, the loop vent is properly called an "Island Loop Vent" and is intended only to be used on island applications were a vertical vent cannot be acheived. In some instances a local inspector will permit a variance allowing a loop vent for other applications.

If you cannot achieve a vertical vent one of the options would be to install an AAV(air admittance valve).

Everytime I "Had" to install an Island Vent someplace than an island or peninsula sink I ran it by the inspector(or Equivalent). They like that kind of stuff, but if he already flagged you for it; most likely he/she is going to want you to install the correct venting solution.

In hind sight you should of asked them what your options were, especially if installing correct venting is too difficult. I wouldn't install an AAV now, that might really piss them off. (Unless of course this is your only option)

In Chicago [Supposedly]we can't use AAV anywhere. We call them Cheater Vents...hee hee hee...

In hindsight, I should have ran this by the inspector earlier. Having seen other advice about using loop vents to solve a few tricky situations made me think it would be ok to use here. Lesson learned, and now I guess I'll do it like I should have to begin with. I'm only out a few bucks for some fittings and a couple hours of my time. No biggee. Thanks for the comments.

Before making any changes you should consider the options and discuss it with the inspector. You may find that he or she may have a specific solution they are looking for, or they may see that you are willing to work with them on this and grant a variance.

I called the inspector at home many times and sought his advice( I know him through work) so I knew my stuff would be OK. I could tell this made him feel important and he was very easy to work with. With plumbing, I came here for knowledge then went to him to approve it before I did it. This made me sound a little educated about it, and made him feel in charge without actually having to take charge I guess. Thats the best advice given for you so far...talk to the inspector some more. Even if you know how to do stuff, and it sounds like you do, he still gets to make the call you know?

Yeah, I made some assumptions here, and I was clearly in the wrong. I went ahead and reworked the sink with a standard through-the-roof vent, it just took a few new tools and a lot of time to drill a 2" hole through a stack of 5 2x4's (one vertical and offset) and the roof. This is precisely why I didn't do it to begin with. I only had one spot about 4 inches wide that I could run the vent, and as I suspected, this stack of 85 year old lumber was riddled with nails. Not only did I chew up the new forstner bit I bought but each time I hit a nail I had to spend a good deal of time and effort to chisel, pull, pull, drive... you get the idea. This took me about 3 times as long as it did to install the loop vent which is why I did it in the first place. Obviously I should have checked with the building department first. I will do so next time.

Again, thanks for the advice.

You didn't say where you live so I give you a little heads up and you can decide if it applies to you.

In regions that are subject to frost we are required to increase the size of a vent to 3" at least 1 foot inside the structure before going through the roof.

Sounds like you used the wrong kind of drill bit.
There are plenty of bits made (even in pipe OD diameters) that are designed to go through wood with nails.
They can be a realchore to use with a hole hawg drill, but can get the job done.

Drilling through wood, pulling on nails, getting drills, & drill bits stuck in strange positions, welcome to the glamorous life of plumbing. It's not all threading & sweating pipe.

I remember drilling through a tough spot, and my bit was at the end of it's life, and this was going to be the last hole for the day; I had my partner hit the head of my Milwaukee Right Angle Drill with a hammer to drive the bit through the wood. Sometimes you have to Improvise with what you got, and Brute Force is sometimes the only solution. Didn't hurt the drill one bit, still got it.

Boy, I thought I knew how to cut metal and wood but, you learn something new every day. I never would have thought of using a Forstner bit to bore thru tubafors. I always think of them being perfect for installing Euro hinges on cabinet doors.

And I could have saved some money if I knew that a hammer-drill meant you drive the motor with a sledge hammer. Geez, I went and bought one that sorta works on electricity; but it makes a terrible knocking sound.

Pinoke

A forstner bit is indeed a poor choice for this task. I scoured Home Depot for something more appropriate but nothing fit the bill. An actual plumbing supply store may have yielded the right tool although my toy drill probably wouldn't have powered it. Improvisation is a DIY-er's best friend!

lazypup, I'm in Portland, OR. I suspect that the vent size increase does not apply here since we rarely get a freeze, and I also see a good number of 1.5 inch vent pipes protruding from neighboring roofs. I guess I'll find out today when the inspector drops back by.

Good news, I passed my inspection. I got a different inspector today, and she didn't even bother to go outside and look at the roof vent or venture into the basement to see what I have left after ripping out the loop vent. All she did was tap on the vent pipe and ask, "Is this under test." Yep. "OK, it's approved." I could have run the drain pipe into a trash barrel!

A bit OT, but she also did the electrical inspection which consisted of a less-than-thorough check to see if I had the proper staple spacing and had plastic grommets on metal boxes. Approved! I guess she was too busy to actually check the circuits, breakers, loads, etc.

Is this how inspections typically work? Do they assume that because I'm going through the trouble of getting a permit that I will follow code? I expected a more diligent inspection of my work, especially considering this is a complete DIY project which is noted on my permit.