I want to replace carpet with hardwood 3/4 oak. There is 5/8 underlayment now with carpet and pad. The top of the stairs already has an oak bullnose with the underlayment behind that. I assume the underlayment would have to come up. The door jambs and trim are now about an inch above the underlayment.The carpet was covering this space before. what is the easiest way to rectify this without taking out the jamb and trim and lowering it to meet the floor?
Re: Hardwood flooring
Rather than pulling out all the underlayment, why not just lay your flooring over the top of it. It'll fill the gap by the doors pretty well. If you had to, you could cut some filler wood and stick it under the jambs. It'd only be about a quarter or three eighths of an inch and it would be pretty unobtrusive. If it's painted (you don't specify stain or paint), it should disappear pretty well. Stain would be a little trickier but still do-able.
It would be easier to remove the bull noses on the stairs I'd guess, than pulling up all the underlayment. Just get taller bullnoses for the stairs or pull up the underlayment on them and possibly install thinner flooring on the stairs to match the elevation of the bullnoses.