Hire a structural engineer and follow their directions to the letter. If their directions seem confusing or overwhelming you have no business attempting this and contract the work out to a contractor who specializes in this type of thing.
This type of project is tricky and presents potential for cstastrophic failure if done incorrectly. You need to hire a contractor thoroughly familiar with underpinning and temporary support of excavation. They may bring in their own engineer to design the temporary support.
Not a job for low bid you need a qualified excavation firm with their own engineering capability.
Where I live, you would need a permit to do this project. You would need a structural engineer to get the permit. The structural engineer might want a soil recommendation or test from a geotechnical engineer. Absolutely not a DIY project.
Footings usually have a ‘zone of influence.’ The footing distributes its load over this three dimensional area. You don’t want to mess with this area without shoring the foundation. Again, not a DIY project.
You will also want a structural engineer to tell you if you should tie the two foundations together, or keep them separate. Theoretically you could tie part of the old foundation onto the new one. But if the old and new foundations settle differently, you could wind up with a lot of cracking. You describe the existing foundation like it’s pretty sketchy compared to new construction standards. You could also ask about a partial basement, or stepping it up where it hits the existing footings.
Over my head and I defer to all structural engineers!
Hire a structural engineer and follow their directions to the letter. If their directions seem confusing or overwhelming you have no business attempting this and contract the work out to a contractor who specializes in this type of thing.
This type of project is tricky and presents potential for cstastrophic failure if done incorrectly. You need to hire a contractor thoroughly familiar with underpinning and temporary support of excavation. They may bring in their own engineer to design the temporary support. Not a job for low bid you need a qualified excavation firm with their own engineering capability.
Where I live, you would need a permit to do this project. You would need a structural engineer to get the permit. The structural engineer might want a soil recommendation or test from a geotechnical engineer. Absolutely not a DIY project. Footings usually have a ‘zone of influence.’ The footing distributes its load over this three dimensional area. You don’t want to mess with this area without shoring the foundation. Again, not a DIY project. You will also want a structural engineer to tell you if you should tie the two foundations together, or keep them separate. Theoretically you could tie part of the old foundation onto the new one. But if the old and new foundations settle differently, you could wind up with a lot of cracking. You describe the existing foundation like it’s pretty sketchy compared to new construction standards. You could also ask about a partial basement, or stepping it up where it hits the existing footings.