I am looking for advice on underpinning a foundation to lower the foundation about 15-18" to obtain a higher ceiling height. It is hard to find documented information on this and some of the people I have talked to have conflicting methods.
The house is located in the Chicago area and was built around 1930, the foundation is concrete 9-10" thick and about 40" high. The footing is about 9x18, this is a rough guess though.
1) It seems you need to work in sections as you excavate and pour a new footing under the existing footing one section at a time. What is the width of each new section?
2) If you are working on multiple sections at a time what is the distance of fully supported foundation, new and old, needed between sections that are being worked on?
3) Is rebar needed? Is so what is the configuration?
4) When you excavate under the existing footing, if you do not disturb the earth below do you need to compact or consolidate the earth at all? If you do disturb it a little, what is the best way to compact the earth in this small space?
5) The concrete form would seem to be earth on 3 sides and a wood form on the front and clean the earth off of the bottom of the existing footing.
6) It seems you can not pour the concrete up to the existing footing to ensure 100% filling of the new footing space. So are you pouring the new footing 1-2" low and then the next day taking non-shrinking grout and packing it in the 1-2" gap?
7) Would the concrete be a typical concrete mix? What would the grout mix be?
8) After pouring the first group of new footing sections how many days should you wait to excavate the next sections which would be right next to the sections just completed?
9) When complete the new floor slab would abut the new footing, rather than sit on top of the footing. Any concerns?
10) Are there any other concerns for a project like this?
I would greatly appreciate any advice on this.
Thanks,
Chris
Foundation Underpinning - How To?
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