What is the basis for the property to estimate that the maintenance fee of equipment and facilities is 5% of the cost?

These two methods are only conceptual, and the concrete calculation suggestions are practical, that is, according to the actual situation on the spot, the conclusion is the most accurate. Although the energy invested is large, it is still very beneficial for daily maintenance in the future.

I mainly want to ask where the 5%-6% fee is stipulated. This is just the average calculated by each family. If not, how to calculate 5%-6%? It's right to be picky about real estate, because you don't have a supporting measurement basis. If necessary, I can send you some cost calculation documents, and you can apply and convert them.