The Biden administration is racing to finalize regulations to curb planet-heating emissions from lightbulbs , automobiles and trucks before a key deadline, after which any new rules could be undone by Donald Trump if he retakes the White House.

With just over six months before the election, at least one major Biden proposal appears to be stalled: an update to the federal housing rules that agency experts estimate would save homeowners nearly three times more money on energy bills than it would add to construction costs, spread out over a 30-year mortgage.

Changing those housing rules would impact about 160,000 new houses and condos built each year in some of the nations fastest-growing and most expensive housing markets. The Biden administration is now looking to the rules as a model for reforming other federal housing programs, which would supercharge the White Houses efforts to curb both emissions and rising utility bills.

But the final rule is inching through the bureaucratic process at an unusually slow rate, taking weeks or months to advance to technical next steps that regulations can typically reach in a matter of days. Its unclear whats causing the delay. And due to a legal quirk, if President Joe Biden loses reelection, Trump could have final say over any rule enacted after May or June.

Critics of the greener housing rules say the changes would raise the price of new homes when half of Americans already say they cant find affordable housing , home ownership rates are stagnating and the bulk of inflation stems from the climbing cost of shelter. Republicans tried to block the rule from taking effect last year.

Requiring new homes to meet stricter energy efficiency standards to qualify for federally-insured loans would add a combined $560 million in building costs, based on a single-year average of construction prices between 2019 and 2021, the Department of Housing and Urban Development found in its preliminary determination last year.

But over the same period a buyer would pay off a house, the thicker insulation and modern windows mandated under the latest model building codes would save the country as much $1.5 billion in energy costs. Some markets could see new homes that save 24% more energy than models built to the previous years standards. The 90-page national blueprint for decarbonizing the building sector the Energy Department published this month calls HUD and other federal lending agencies to swiftly adopt the latest codes.

A spokesperson for HUD declined to comment on whats causing the delay.

HUD is in the process of finalizing the determination, recognizing the interest in doing so as promptly as possible, the spokesperson told HuffPost in an emailed statement Friday.

The U.S. has no official nationwide building code. Instead, states can choose to adopt model standards written and regularly updated by private code-writing organizations such as the International Code Council, a nonprofit that convenes local governments, utilities and construction industry professionals. Compared to previous rounds of codes, the ICCs 2021 homebuilding guidelines delivered double-digit improvements on the energy efficiency of new homes.