The entire vertical load of your structure terminates here. Compromises in soil compaction, concrete psi, or rebar placement will inevitably manifest as catastrophic failure in the upper levels.
Standard undisturbed soil bears roughly 2,000 psf (pounds per square foot). Prior to pouring footings, procure a geotechnical report confirming soil type and bearing capacity. Clay soils expand aggressively when wet, demanding deeper excavations to bypass the frost line and reach stable substrata.
For load-bearing foundation walls, specify a minimum compressive strength of 3,000 to 4,000 PSI concrete. Incorporate air-entraining admixtures if the foundation is exposed to freeze-thaw cycles. Slump should not exceed 5 inches during pour to prevent aggregate separation and weakening of the cured wall.
Damp-proofing (tar) is obsolete for modern renovations. Insist on true waterproofing membranes—elastomeric asphalt applied at 60 mils thickness, covered by a dimpled drainage board. Couple this with a rigid PVC weeping tile system laid in washed gravel at the footing perimeter.