My home currently has a step down into a 12' x 20' sunken living room. I would like to raise the floor in the sunken area to the same level as the adjoining dining areas and remainder of the first level of the home. There is a crawl space located under the floor with 2x10 floor joists spanning the short direction. Is it better to remove the existing floor and span it with similar beams blocked up as required off the sill plate or to build directly over top of the existing sunken floor and possibly span the new joists the opposite direction, i.e. using the existing floor as the load bearing surface? Either way I will have to raise heat ducts and electrical outlets. Any advise on the structural aspects?