We have a New England home where the basement has a rubble wall and a dirt floor under gravel.

Some point during the last 30 years someone dug down, placed a vapor barrier, and then placed 2-3 inches of gravel over that.  Then large wooden pallets were build to allow dry storage.

Because of changes in landscaping (we think), water now leaks into the basement with rainstorms, bring in water and silt at numerous places along the periphery.  Sometimes water will accumulate up to 1.5 inches over the level of the gravel.

The water is slow to drain - we think because of the vapor barrier.

In addition, over the last 3 years I have seen two areas of the vapor barrier start to come to the surface.

We are now undergoing a big renovation and will be excavating a new frost wall foundation to allow us to build an addition.  We will not be making it basement depth because this might undermine the existing rubble basement.  We will be doing site work to improve the drainage AWAY from the house and will either have a dry well or connect to daylight (at a nearby slope) to drain footing drains.

We have been advised to remove the current 2-3 inches of gravel (and dirt, as long as we don't undermine the base of the rubble foundation), place a new vapor barrier, and then pour a 2 inch rat slab of concrete, and then place a sump pump well somewhere (one would be to slope the concrete toward the middle).

Questions:

1.  Does this plan sound reasonable (since we are digging anyway)?
2.  Does the vapor barrier and rat slab decrease the moisture in the HOUSE and will this improve the house performance?
3a.  Is it worth doing any insulation under the rat slab?  Understanding that head room is at a premium (this is not a finished basement - we just want dry storage).
3b.  Is it still worth insulating under the slab without insulating the rubble walls?

Hope this is enough info.  Thanks for your thoughts.

Joe

Drain-tile and put in a sealed sump and pump in your basement! Over that poly with taped and or glued seams, Extruded Polystyrene insulation with taped seams, then slab. That is cheap and easy (now), it will be a lot more after the work is done and there is a basement floor.

Drain-tile and drain to day-light if possible, all the exterior you can. Again now is the time to do it. Grade properly! This is much easier to do it your addition is ICF to the roof.