My sunken living room floor is concrete slab surrounded on two sides by higher concrete slabs at the level of the rest of the house. The other wall is a brick fireplace hearth. The wall opposite that is a sheetrock exterior wall. It is an area about 13' x 10' which is much too small for a "sunken" anything in my book and is just a hazard for an old woman (me) to fall into. One of the concrete side walls is the entryway at the front door and is far too narrow as well. I want to raise this floor to the level of the rest of the house and I have ceramic tile to do throughout the house. This area is about 6 inches deep. What is the best and possibly cheapest way to fill this in and level it off?
One way to raise the floor, and possibly the most reasonable cost wise, is to install what I would call sleeper joists sitting the top of the existing subfloor and than add new subfloor covering over those.
These "sleeper joists" would be installed as 2xX material on edge. This could be 2x6 planks spaced 16" apart. It may be necessary to rip the 2x6 planks to somewhat less than their native 5.5" width so that the subfloor and whatever flooring that you choose to put on top of that would match to the adjoining floor heights.
So its a shallow concrete pit in the floor? With concrete on five sides? I would fill it with concrete - either straight concrete if it was shallow, or put a layer of gravel in to save on expensive concrete.
Downsides, this is likely to cost a lot more than the wooden floor suggested already, but you could park a car or grand pianos on this without concern. Also, its NOT easily reversible like the timber solution.
Since the area is backed by concrete already, you might get away with no reinforcing in this, though I'd probably lay some mesh in there anyway. You would use a suitable etching fluid to "key" into the existing concrete surface.
The hardest part would be getting the fill and liquid concrete into the room. That would be a lot of stone to move.
A square yard of gravel with a depth of 2 in (~5 cm) weighs about 157 pounds (~74 kg).
concrete is about 150 pounds (72 kg) per cubic foot
You have roughly 3 yards x 4 yards, so 12 square yards and 4-5 inches deep which is about 4700 pounds or 2200 kilograms of gravel.
Concrete on top would be between 1600 pounds for a 1" thickness, and 3200 pounds for 2"
A contractor's wheelbarrow full of wet concrete is around 80 lbs.
So you'd have to carry very approximately 75 contractor wheelbarrows of fill and 25 barrows of concrete through your house to the area.
I'd build a shallow ramp to go over any door steps, and would line any access routes with cheap plywood on the floor and plastic up the walls to save damage. You would also want to completely empty the destination room of furniture, and cover at least the lower walls and fireplace.
What have I missed about pouring new concrete butted to existing concrete? Given its a solid box already, there's little need to tie the old and new together with anchors. And the new concrete is only going to be subject to compression not tension.
The concrete will take a couple days to cure, and then up to a month to cure completely. If you find the lime-smell of concrete unpleasant, you might want to sleep elsewhere for a bit. Venting the room via open windows and breeze will help.
Expect to not walk on it for days, and leave it uncovered for as long as possible. Perhaps throw some temporary carpet on top, but I would not start tiling for at least a month after initial pour.