Correcting A Sagging Floor
The homeowner said the dwelling was less than four years old with a greater than a five inch sag in the floor of their 38' x 50' living room. Several contractors had suggested the only means of repair would be to move out every piece of furniture, brace the walls, remove and replace the floor system that was Mexican tile over 1-1/8" plywood sub floor.
The only crawl access was more than 100 feet away from the sagging floor section. There was no cross ventilation. When I reached this area the air was damp and heavy. Fungus was growing on the rotted glu-lam girders and floor joists. Pier posts had rotted in their metal brackets.
Plywood shear panels easily crumbled with a soft spank with the palm of my hand.
We cut the tiled decking outside the living room, excavated an access ramp, and cut a window in the foundation. Damp air, under compression billowed out of the window for some time.
Additional pier footings were excavated to allow the introduction of smaller support beams. 
Breaking new windows through the foundation stem into the new air shaft. 
Two men were required to operate these heavy 90lb jack hammers in a confined 18" space.
Smaller 30lb hammers were used to trim the window to size.
New treated floor joists were introduced adjacent to the rotted members.
New joists were shimmed and blocked then tied to new girders with wood screws and framing anchors.
A self leveling transit was used to monitor progress in the lifting process.
He new girders and joists were lifted methodically to re-establish the floor plane.
The final remnants of the rotted glu-lam joists and girders were hauled to the city dump.
The appreciative homeowner gratefully writes a final project check for the successful restoration of the floor system to its original plane. All of this without moving any furniture or cracking any of the Mexican floor tiles.
