Footing Question

[bcanoe]

I am about to start a project where there is a crawl space. The hole has been dug and we have hit rock all the way around. The rock is slopeing 18" below natural ground on the high side to 4' on the lowside. My question is can I fill the lowside with crushed stone so that my footing can be formed at the 18" depth or do I need to put step footings down to the 4' area?

[gkdesigntech]

I'm not really following your question completely but I can tell you this - the IRC requires all footings to be below the local frost line unless they are on solid rock. There are also requirements for footings on sloping grade as well. If you're interested you can send me some photos or sketches of your situation and I'll try to answer your question. You can email me at design_tech@windstream.net

[concretemasonry]

Crushed rock cannot be compacted suitably to place a footing or wall on. If you happen to get the right combination of fines, you can compact it if you have some lateral restraint to hold the compacted fill in place while you compact it.

You would probably be better off stepping the footing since you only have a 2.5' drop. If it is a poured foundation wall on a strip footing of a poured wall bearing on suitable rock, you will have to match the form widths to the rock contour. If you go with block, you will have more latitude in the horizontal dimension because you can adjust the block length and the head joint width.

Depending on your frost depth you might be beter off putting a strip footing in a portion of the lengths that do not require the full 4' depth.

Dick