New here & planning my first flooring project.
I'm planning to install prefinished solid 3/4" x 3 1/4" oak on the second level of my house. (Not over a crawl space) I would appreciate some opinions on just how important it is to use a tarpaper vapor barrier here? In my thinking, I don't need it, but don't want to omit a fairly simple step if it has any value at all. Also, I would like to use some glue in the closets & only nail where I can get the nailer to fit. All comments are greatly appreciated.

First, dont confuse vapour barrier with vapour retarder, which is what tar paper is. Secondly you should'nt need it with a finished ceiling below. Up here we traditionally used a wax coated paper which is essentially useless a vapour barrier or retarder, but at the beginning of this year, I decided to swim upstream from the norm and apply on all main floor subfloors, a product called V-LOK from Armstrong which has significantly reduced our calls regarding "cupping"

If you are going to glue some boards in place, use a urethane based adhesive that will retain some flexibility if the floor needs to move at all due to humidity fluctuations.

IMHO, just do yourself a favor and use the tar paper. The debate has been had time and time again on this board and hundreds of others, so let's avoid the discussion on whether it has any effect or not. The bottom line is NWFA guidelines require it, every manufacturer requires it, you're not saving hundreds of dollars by not using it, so eliminate any excuse for someone to try and void your warranty and follow the directions as they are written.

Totally agree with BW.

Dennis, why skip from the most basic of material to the top shelf stuff without using 15 lb? Paper too heavy for the guys?

Well, actually I dont think I suggested skipping it, just said that it A: wasnt a moisture barrier, as the poster thought, and B: that it wasnt necessary to the install. If I ever caught one of my guys not using an underlay, he would be very quickly standing in the soup line, lol.
Unfortunately, here in Ontario, all that is required is a wax paper, which does very little as a vapour retarder, but it does help the installer pull up the boards, since it is slippery. In an effort to do our installs in a close to correct manner, we use V-LOK on all main floors, and continue with the stupid wax underlay in the second floors.
Note that the V-LOK costs 10 cents a foot, and the wax underlay about 1 1/2 cents a foot. Not a big deal? We install on average, about 10000 feet per day so it does mount up. We add this cost on private jobs, but the builders we work for are a bunch of cheap you know whats and will pull a contract away from us if they find someone 5 cents cheaper than us.

On the upper floors, anything for a slip sheet. It doesn't have to be asphalt impregnated roofing felt. This is perfect for rosin paper, newspaper or anything so there is not wood to wood contact between the subfloor and flooring.