I am going to be installing 3/4" pre-stained hardwood in my house. I have a questions about the 3/4" gap you leave against the wall. Do you leave 3/4 from the drywall or do you undercut the drywall so it goes under it? I have 1/2" drywall.

I just couldn't help but notice that's a pretty big gap. The trim in the house is pretty thin i don't think adding quarter round would cover it.

We've discussed this ad nauseum. The 3/4" "rule of thumb" is a pretty ridiculous recommendation for most home installations. 1/2" is typically more than enough, even for floaters. However, if you're using thin base, then yeah, undercut the sheet rock about 1" up from subfloor and use just a 1/4" space. You can do a search of this subject on this forum to understand the reasoning if you want.

Thanks

Also, keep in mind that the expansion tolerance is mostly needed on the parallel walls. Wood does not expand to any great degree in its length, only across the face. When cutting the bottom of the drywall, you will probably intersect the nails or screws attaching it to the wall plate so you will need to refasten it in all likelihood.