Tiburon became the third U.S. city to mandate solar energy system installation in new construction in February 2015. The city's zoning code requires new single-family dwellings to install solar PV capacity of either 2 watts per square foot of gross floor area (prescriptive calculation method) or that offsets at least 75% of the building's annual electrical load (performance calculation method). The Design Review Board may grant a waiver for unusual or several practical difficulties due to physical circumstances of the site, though the dwelling unit may need to meet other green building requirements instead.