I am wanting to build an addition on to my existing home which is on a slab. The side of the home that the addition will set on is a hillside which is moderately steep. Therefore, I am wanting to put a basement in to maximize living area. My question is: How do I lay up a foundation wall under the existing footer & slab without it giving. The total length of this wall will be 34'. Also, once I get the wall in, how do I waterproof it? I would greatly appreciate any help from anyone with the experience to give me any ideas. Thank you.