Final answer:
Upgrading an existing building to meet current codes often involves renovations to the electrical system, HVAC, and sometimes plumbing, rather than the foundation.
Step-by-step explanation:
The renovation of an existing building often requires upgrading to meet current building codes, which can include enhancements to safety and livability features such as structural integrity, fire safety, and the performance of essential systems. In general, such upgrading most frequently affects the electrical system of the building, as it must be capable of handling modern demands and safety standards. Other systems typically involved in these upgrades are the HVAC system, for efficient heating and cooling, and sometimes the plumbing system, to ensure proper sanitation and running water. Although the foundation of a building is crucial, it is less often the subject of an upgrade during renovations unless it is found to be unsound or inadequate for new loads or uses.