The bigger problem is likely water - both use and removal. Most offices will have a couple bathrooms per floor and a kitchen. Those are used frequently 9-5 but

The bigger problem is likely water - both use and removal. Most offices will have a couple bathrooms per floor and a kitchen. Those are used frequently 9-5 but rarely on nights and weekends and there's no heavy usage like showers or clothes washing. If you build 100+ apartments, you need to either build 100+ bathrooms and kitchens (expensive!) or do it dorm style with common spaces plus private bedrooms. That brings it down to a smaller number but still probably 5:1 for 20+. That's just on the consumption side. And the entire infrastructure - both inflows and outflows - are probably not sized to handle that change in usage. It's definitely not impossible but the conversion costs are massive.