The city council is still hashing out updates and clarifications to its green buildings law passed in April. It’s considered the most ambitious and exacting city mandated building emission measure in the world.  Some of the details though will take months and years to work out. That has building boards scrambling and struggling to figure out what this means for them.

Andrew Werner is the president of his Upper East Side co-op and the building was all set to convert its old oil heating system to natural gas.

“Making our buildings more efficient is absolutely the best way to go,” said Werner who hired En-Power Group, an Energy Consulting and Engineering company.

“It is certainly one thing that would actually help on the energy footprint, carbon production, but there’s obviously other challenges,” said Michael Scorrano of En-Power Group.

The big challenge he says is the city’s new Climate Mobilization Act, the so-called Green Buildings bill passed in April. It mandates that many city buildings 25,000 square feet or more dramatically reduce their carbon emissions by 2030 or face stiff fines.

“Starting in 2030 they would have about a $25,000 ding every year, just for being with the current energy use they have,” said Scorrano of Werner’s building.

Werner says converting to natural gas seems like a no-brainer, but he adds the building cannot move forward because kinks in the new Green Buildings law have to be worked out.

“The bill is not clear,” he said.

Experts say the law does not lay out exactly how much money natural gas conversion would save in fines or if other energy sources would be better.

“We have about 6 months left; 5 to 6 months left before this window closes on the incentives from Con Edison are potentially off the table.

That means the pressure is mounting because once the Con Ed incentives disappear, the cost they says of converting to natural gas doubles to $600,000 from $300,000 dollars.

For co-op owners, who would have to ultimately absorb that cost, it would trickle down and double. In some cases that would mean additional maintenance or an assessment changing from $10,000 to $20,000.

“It’s very frustrating,” said Werner.

Some of the owners in his building are young families and seniors on fixed incomes.