All new homes in Palo Alto will have to dedicate roof space to solar panels under a new law that the City Council is preparing to adopt later this month.

The roof requirement is one of several changes to the city's building code that the council will discuss on April 20. The council is also expected to approve new rules geared to promote irrigation efficiencies and a new energy "reach code" that would require buildings to exceed the minimum state energy requirements by 15 percent.

The new rules would build off an effort that the City Council first launched in 2008, when it adopted a Green Building code that requires new developments to adopt energy-efficiency measures that had been optional under the state ordinance.

In the years since, the council has made numerous changes to the building code, including recently adopted requirements that new buildings be wired for electric-vehicle charges.

Now, the focus is on sun and water. The new solar-panel requirement would require all new single-family residences to be "solar ready." In addition to dedicating 500 square feet of roof surface to potential installation of solar panels, the builder would have to provide conduit to support the future wiring for a solar system. Exceptions would be granted in cases where protective trees may be affected by the solar-ready zone, according to a new report from the Development Services Department.

On the water-efficiency front, the city is planning to adopt a rule requiring a "laundry-to-landscape ready" irrigation system. New construction projects would be required to install a three-way diverter valve in the drain line of all laundry fixtures, according to the staff report. The installation of such a valve would enable a homeowner to easily install an irrigation system utilizing grey water.

"It's a progressive ordinance," Development Services Director Peter Pirnejad told the council's Policy and Services Committee on March 20, when the committee discussed the proposed changes and gave them its blessing. "It is very forward facing. It's ahead of other cities and we don't shy away from that."

Pirnejad also noted that the state codes are also moving quickly toward requiring greater energy efficiency. The 2013 California Green Building Standards Code includes "various environmental-performance requirements related to site design, water efficiency, material conservation and air quality issues."

"We're ahead of the curve, but the curve is right behind us. And it's a tidal wave and we're just staying one step ahead of it," Pirnejad told the committee on March 20.

In its March review, the Policy and Services Committee proposed several minor changes, including an exemption for buildings in which strict compliance is infeasible or cost effective. This would allow staff to permit alternative measures to achieve performance targets. The committee also suggested revising the threshold for residential projects that would have to comply with the local "model water ordinance" (staff had proposed applying the ordinance to projects with at least 1,250 square feet of residential space; the committee recommended lowering it to 1,000 square feet).

The committee also requested more information about the costs of complying with the new laws and about the estimated greenhouse gas savings that the ordinance updates would achieve.

Councilman Pat Burt, who chairs the committee, noted during the conclusion of the committee's discussion that there has been a trend in recent years of seemingly ambitious goals becoming "the next generation of standard practices."

Burt predicted that the new laws will follow this pattern.

"Things that seem to be real challenges – we stretch ourselves and next thing we know they are readily accomplished," he said. "I look forward to this falling into this category."