Mayor Kirk Caldwell on Wednesday allowed a bill designed to be a comprehensive policy on large-scale houses to become law without his signature, warning that it may go too far and have unintended consequences.

Caldwell said he supports stemming the growth of monster houses and other large detached dwellings and noted the city’s Department of Planning and Permitting had submitted its own bill to tackle the issue.

He wanted to sign Bill 79 (2018) but the Council added too many new wrinkles, he said. “It became complicated, it became difficult to implement, there’s discretion,” he said.

The Council passed the bill April 17 by a 9-0 vote, a veto-proof margin.

Kymberly Pine, chairwoman of the Council’s Zoning Committee, authored the latest draft. She said more than 200 stakeholders gave input on the bill and were satisfied with the final draft. “We worked with builders and homeowners to ensure we protected the public from illegal structures while not over-regulating the construction industry.”

Caldwell needs to stop making excuses, she added. “Few regulations and a lack of enforcement led to the proliferation of monster homes.”

The Council has grappled for several years with how to curb the spread of such houses, which go up quickly, often defy city building rules and dwarf other homes in older residential neighborhoods. Critics say the structures overburden infrastructure and are often used as illegal rentals, vacation homes or other nonconforming businesses.

But proposals to address the issue also triggered a backlash from lawful home builders who warned that new regulations might further delay the issuance of building permits from the Department of Planning and Permitting, which already is has been criticized for taking too long to approve permits at a time when demand for housing is high.

Caldwell and the Planning Department’s acting director, Kathy Sokugawa, said they will monitor the new law and likely draft legislation for the Council to consider “so that we’re not delaying permits and we’re not having unintended consequences.”

The key component of the bill caps the maximum density of a detached dwelling at a floor area no greater than 70% of a lot’s size, or a floor area ratio (FAR) of 0.7. The typical 5,000-square-foot lot could have a 3,500-square-foot house on it.

Any house with an FAR greater than 0.6, however, would need to be owner- occupied and be subject to additional rules including 8-foot side and rear yards.

Caldwell said he supports an FAR limit. Currently, the law places no limit on density but prohibits a structure from covering a footprint, defined as “lot coverage,” greater than 50% of a lot’s size.

Sokugawa said she supports a minimum of two on-site parking stalls, plus one stall for each additional 750 square feet over 2,500 square feet.

But the two raised concerns about the stipulation that a maximum of 75% of a property can be covered with an impervious surface, such as concrete or asphalt, leaving at least 25% to be grass or some other material that can absorb runoff. Sokugawa said the issue needs to be explored further.

They also dislike language in the bill that regulates the number of bathrooms and wet bars allowed per zoning lot, not per dwelling. “There are many older communities with older lots with many houses on them, more than one or two,” Sokugawa said. “But this bill specifically says how many bathrooms you can have per lot.”

Gladys Quinto Marrone, CEO of the Building Industry Association of Hawaii, said her group preferred an earlier version of the bill.

“We appreciate our mayor’s insight on potential unintended consequences for legitimate builders,” Marrone said. “BIA will continue to work with the DPP to ensure that the law does not inadvertently impact families who want to build a legitimate larger or multi-generational home.”

Tyler Dos Santos-Tam, a spokesman for the community group HI Good Neighbor, said the version of the bill that passed is a solid compromise.

“While (DPP) claims that Bill 79 will require them to perform more plan checks and additional reviews, that is precisely the point,” Dos Santos-Tam said. “Monster homes have proliferated because the city approved plans without thorough vetting and allowed so many of these homes to slip through the cracks. We support efforts to provide DPP with more staffing, additional tools, better software, and more.”

Several Council members have asked if more inspectors and plan checkers would help DPP. Pine last year inserted into the budget 10 more inspector posts that have not been filled.

Caldwell said DPP continues to have a difficult time hiring and retaining employees.

The bill is supposed to take effect upon it becoming law, which typically is a few days after the mayor approves or allows a bill to become law without signature.

“We have a very short amount of time,” Sokugawa said.

The bill would not have an impact on any houses already built, she said.