"If we're altering a usage, I usually want to advocate grandfathering," she explains. Assume it's a rental limitation. That is a significant concern and a shift in use. So let's grandfather owners who are currently renting out their apartments and apply the regulation to new owners from now on. This gives owners time to find a new landlord or sell their apartment. She also recommends giving tenants time to move out if you're changing the number of bedrooms in an apartment building. Again, this is important because it prevents people from moving in only to find that they can't rent out their unit anymore. It also gives landlords time to find new tenants if they want to increase the value of their property by adding beds or bathrooms. Last but not least, you should consider grandfathering changes that affect how much people pay for an apartment. If you raise the price of an apartment without telling your customers, some of them will be forced out of their homes and have no choice but to look for another place to live. This is bad for everyone involved: tenants who can't find new places to stay, other tenants who have to share their neighborhood with more people, and owners who need to make up for lost revenue by raising prices further or selling their properties. In conclusion, using grandfathering when making major changes to existing regulations ensures that people don't lose their homes or pay more for their apartments.