Yes, replacing a foundation typically requires a level house as a starting point. It is concerning that the need for house leveling was not mentioned during the initial assessment or quoting phase. Generally, when replacing a foundation, it is crucial to ensure that the structure is properly leveled to maintain structural integrity and prevent future issues. Leveling a house involves adjusting the foundation and structure to make it even and straight. This process may involve lifting or shoring up certain areas of the house, depending on the specific requirements. It is essential for the new foundation to be aligned correctly with the rest of the structure to avoid problems with doors, windows, floors, and overall stability. Given that your house is over 100 years old and built on a sloping hill, it is not uncommon for houses of that age and location to require some level of leveling work. However, it is concerning that this additional cost was not disclosed earlier. It's important to communicate your concerns with the company and ask for an explanation regarding why this requirement was not mentioned beforehand. Consider discussing the situation with the company and requesting a detailed explanation of why leveling is necessary now and why it wasn't identified earlier. You may also want to consult with another reputable foundation specialist or structural engineer to get a second opinion and to evaluate the situation thoroughly. Ensure that any additional costs, such as leveling, are clearly outlined and documented in the contract or agreement with the company. It's essential to have open communication and a clear understanding of the work being done and the associated costs to avoid any further surprises during the project. If you have concerns about the company's approach or pricing, it may be worth exploring other options or seeking professional advice to ensure the best outcome for your house's foundation replacement.