mike_aa said:
If you are using a double plate on the bottom, would it make sense to offset the bottom one out from the wall by .5 inch so you can set your drywall on that to achieve the 1.5 inch spacing?
That would be a real pain to frame for not much gain. Your floor is un-likely to be perfectly flat, so having that gap under the drywall gives it a margin of error to hang, it might hand over that lower 2x4 or even leave the upper one a bit exposed. That gap also gives a spot for the flooring, if you have a floating floor, it's a space for the gap and makes your trim board less critical to cover the gap. If you are putting down tile or similar if gives you working room at the edge. I get what your thinking, it would just be more work. You also don't want to find after you put the drywall up, that your lower 2x4 sticks a bit further out than the face of the drywall, now you will have to deal with that when putting on trim. The last part is by bringing the wood out you increase the chance of a water transfer from the floor as water will get in the wood, putting the wood under the drywall gives it one more path for moisture transfer.