In addition to the construction advice already given, there are also insurance issues that will need to be resolved. You may not have thought about this, but it is very important that you run this project by your insurance broker before starting to do any work.
1. A standard exclusion on General Liability insurance is XCU (Explosion, Collapse, Underpinning). You will have to get this coverage added to your policy, otherwise your insurance will deny any claim if the levelling procedure goes wrong. Here is a sample excerpt of the exclusion:
"Structural property damage" means the collapse of or structural injury to any building or structure due to:
.....a. Grading of land, excavating, borrowing, filling, back-filling, tunneling, pile driving, cofferdam work or caisson work; or
.....b. Moving, shoring, underpinning, raising or demolition of any building or structure or removal or rebuilding of any structural support of that building or structure.
This coverage is not cheap, however, you can buy it with the Explosion peril still excluded; so in other words you are only buying the C&U cover.
2. In addition to having the above standard exclusion removed, you will likely also have to have your Liability rating revised. If you currently are insured as Residential Remodeling or Interior Carpentry, then you may not be covered for major structural modifications. A different (higher) rate may have to be added which will result in an additional premium adjustment. Your W/C rates may have to be adjusted as well. Again, check with your insurance broker.
You should also get your broker to give you quotes for the additional insurance costs if any of the above changes are required. That way you can make sure to include those extra costs when you quote the HO.
An option may be to sub-contract out the structural levelling. Make sure you have a strong indemnity agreement and that the sub-contractor has added you as an Additional Insured on their policy so that you are protected if you get pulled into a lawsuit caused by the sub's mistakes.
3. Last, because there was previous work done to level out the home, you could end up in a mess of a claims adjustment if at some future date the house has ongoing structural problems. If that previous work was done many years ago, the statute of limitations may have expired on suing the first contractor even if future engineering reports show that they were negligent. Your insurance policy could then be stuck paying for a major future structural damage claim even if you only did some minor adjustments to the first contractor's work.
As a future claim would be considered a Completed Operations claim, that means that you will have to keep the extra Liability rate line for "structural construction" (see Item 2. above) on your policy for as long as your contract warranties completed operations and/or the statute of limitations in your area. I am not sure what is usually found in residential construction contracts, but the standard in commercial is minimum of 2 years and most public works require 6 years.
Sorry to add to the list of concerns, but I would hate for you to find out after the fact that you don't have the correct insurance or that you didn't budget for any extra costs. These are issues that you should get resolved with your insurance broker to make sure that you are adequately insured before proceeding with this difficult project.
P.S. - To drive home the risk of ongoing future problems, I added a photo of a famous "levelling" project that has been ongoing for 800 years and is still unresolved. :laughing: