When the 2012 International Energy Conservation Code (IECC) takes effect in January, it will raise the energy bar more than any previous code, with a targeted 15% jump in the energy efficiency of new homes vs. the 2009 code and a 28% improvement over 2006. Getting over that hurdle will challenge builders and inspectors.

The new code follows the lead of the 2009 version–the one currently in use–which was the first to spell out requirements that had only been generally stated in past versions. For instance, the 2009 version requires half of new lighting fixtures to be hard-wired for high-efficiency bulbs (LEDs or CFLs), and it includes detailed specs on air-sealing the building envelope as well as the home's HVAC ducts. "In the past, the code was relatively ambiguous," says Mike DeWein, technical director at the Building Codes Assistance Project, a Washington-based initiative that helps regulators to adopt and builders to implement energy codes. "Now it tells you how to seal, and where."

The 2012 code goes even further. For example, it demands more insulation and better air sealing, raises the hard-wired fixture requirement to 75%, and no longer lets HVAC contractors use building cavities as supply or return air ducts.

Which requirements will be most challenging will depend on where you build. In Minnesota, state Energy Specialist Don Sivigny predicts the air-sealing requirements will force some builders to switch from exhaust-only ventilation, which relies on a leaky building shell, to full mechanical ventilation with make-up air. He says this will be a learning curve for many builders, and expects the state will have to offer training.

"If the builder doesn't understand the code, we don't get compliance," he says.

Mike Turns, associate director at the Pennsylvania Housing Research Center, says builders in his state have long done a good job with envelope air sealing, but the 2009 code's duct sealing and duct testing requirements were new concepts and have met resistance from many builders and HVAC contractors. "It's another subcontractor that has to come to the site, and another inspection," Turns says. And he expects things to get tougher next year. "My guess is that 90% of HVAC contractors here use building cavities as return ducts," Turns says. Eliminating that option is "a big deal."

Not all states and jurisdictions will adopt the new code, and in those that do it won't always be consistently enforced. In Keene, N.H., code official Medard Kopczynski estimates that just one-third of the state's inspectors fully enforce the 2009 IECC. The rest deal with the code by requiring only plan review but no inspection, or by just ignoring it. In Pennsylvania, Turns has seen a lot of selective enforcement, an example of which is the light-fixture requirement. "I don't think most inspectors go around counting light bulbs," he says. The story could be repeated in other states.

Uneven enforcement is a consequence of tighter state and local budgets, which have cut inspection staff, leaving not enough inspectors for even a reduced construction volume. When inspectors have to choose which codes to enforce, energy seldom gets priority. "A lot of departments see their main responsibility as life safety, and energy can take a back seat," says Stephen Kanipe, a building official from Aspen, Colo., who also is a code trainer for IECC.

There are different thoughts on how best to address this problem. DeWein claims to have heard regulators and builders suggest the IECC change from a three-year to a six-year code revision cycle, so the industry can have more time to absorb changes. However the International Code Council, which writes the IECC, as well as a number of code officials say that the three-year cycle is needed to ensure that the code can keep up with new technologies.

Another option would be to make changes more gradual. "We can get [to the ultimate goal] by more modest efficiency gains, say 7% per code cycle rather than 15%," says Bill Fay, head of the Energy Efficient Codes Coalition. Fay believes that most state s will ultimately adopt the code. However, he believes that moderating the pace of change will lead to more voluntary compliance: something everyone prefers to enforcement.