I hope someone is kind enough to help me with three newbie questions:

1. If a fireplace hearth is framed around with a mitered frame is it not at risk of cracking from pressure from expanding floor (e.g. a marble hearth)? Is it necessary to leave a gap and cover w/ t-moulding or is framing directly against the hearth with solid flooring acceptable?

2. I have an existing floor I am butting up against. There is a horizontal strip layed where the existing wood met carpet being replaced with a new floor. Can I just run the new floor into the perpendicular strip already in place that also runs perpendicular to the existing wood floor? Or again, is a t-moulding necessary to hide gapping? (The existing wood floor that terminates in this perpendicular strip of wood has not shown significant gapping there. I don't know if perhaps it was glued as well as nailed?)

3. With regard to leveling an uneven subfloor w/ builder's felt is there a maximum amount that should really be leveled? There are some very high spots on the subfloor - perhaps 1/2" over 4' in a few spots where OSB T&G joints crowned.

Thank you,

Tom