extend/increase height of basement concrete floor:

[cm.garvey]

Greetings. I'd like to raise this rectangular area to the same level as the basement floor (see pics). I assumed that best way would be to:

1) build a hollow wall/concrete forms on open side, and fill it with concrete, let it dry
2) dump a bunch of gravel or sand into newly enclosed area, leave room for 3-4" of concrete to pour on top

Is this the right approach? Any other ideas or tips?

much appreciated--

 

[Sparky617]

You'll want to compact the stone you put into the space, put in 3-4 inches and compact, put in another 3-4 inches and compact until you get to the desired level. You could just fill it with concrete but that would be a lot more expensive. But if you were buying Redi mix you'd probably need to buy that much anyway. To figure out how much concrete you'll need measure length x width x depth in feet (4" equals .33 feet). There are 27 cubic feet in a cubic yard.

So if it was 1' deep, by 3 feet wide, by 4 feet it would be 12 cubic feet of concrete or I bit shy of a half a cubic yard. Hard to get that delivered. If you put in enough crushed stone to reduce it to 4" it would be .33 x 3 x 4 = or 4 cubic feet, easily enough to do with bags of concrete from the home center.

 

[cm.garvey]

Thanks, good stuff. Someone else just suggested that I could fill the void with rigid foam, then dump 3-4" of concrete on top of that. I have enough rigid foam already here to do this. Thoughts?

 

[Sparky617]

Thanks, good stuff. Someone else just suggested that I could fill the void with rigid foam, then dump 3-4" of concrete on top of that. I have enough rigid foam already here to do this. Thoughts?

They will put extruded polystyrene under concrete slabs to insulate floors, so it should be OK. Might go with a slightly thicker slab though and add some rebar or mesh.