At some point for ZNE it moves away from "% better than code and then buy solar" to "can we stay under our solar budget?"

Your solar budget is:

24,000 sf roof * 90% roof area utilization * ~19 W/sf (assuming flat, high-efficiency panel) * (1 kW/1000 W) * 1,100 kWh/kW-yr = ~450,000 kWh/yr, or a roof production of 62 kBtu/sf-yr.
If you have 7 floors, that means your overall EUI target for the building is about 9 kBtu/sf-yr.

This will be very difficult to hit. You need more energy production. Some ways to do that are:

• Elevate solar above roof, to get full area (increases target to ~10 kBtu/sf-yr)
• Add solar to facades /shading / canopies
• Figure out another energy source

I think you may be able to get down to ~20-25 kBtu/sf-yr through energy efficiency measures.

"Mandatory" measures:

• All LED lighting
• Energy Star Tier 3 appliances (refrigerator, dishwashers, etc.) + induction cooktops
• Lots of insulation, good windows

Also consider:

• Solar hot water heating
• Heat pump water heater
• Drain Water Heat Recovery
• Sewer line-integrated heat pump/heat recovery
• Compact Hot Water Distribution
• Low-flow showers, common laundry
• Each unit gets a Heat Recovery Ventilators instead of bathrooms exhaust fans for ventilation, with spot boosting for kitchen range hoods.
• VRF heating/cooling or central heat pump serving baseboard hot water loop in each unit (+mass and radiant if you have the $)
• Ceiling fans provided for each unit
• Hit a target infiltration rate with airborne sealant deposition. (Aeroseal, the duct sealing company, now provides a service to seal multifamily units and hit a guaranteed infiltration rate. <1 ACH50 infiltration).

California is requiring all new homes to be ZNE in 2019, including multifamily (I'm not sure how they handle multi-story buildings): http://www.californiaznehomes.com/

You can see a list of the measures they are considering for this in presentations here: http://title24stakeholders.com/meetings-workshops/