Philadelphia includes in its housing code a provision for voluntary affordable housing. Moderate income units will be priced at levels affordable for 60% AMI, while low income units will be priced for 50% AMI. Where at least 50% of gross floor area will be designated for residential development, floor area, height, or dwelling density bonuses may apply. The bonuses are calculated depending on the zone and income designation. These affordable units must constitute at least 10% of all units, be affordable for 50 years, and be of comparable quality.