Building Codes and Green Rating Systems
Building codes are laws created by governments to ensure minimal levels of health, safety and performance. Historically most of these codes addressed only safety and simple health issues. Houses had to meet a level of structural integrity so they would survive normal "severe" weather and usage conditions: a house that meets code will support a room full of people, survive a big snow storm, live through the average hurricane, etc. Fire regulations help prevent it from burning down and electrical code keeps the wiring safe. In addition the health department keeps the water clean and prevents sewage from infecting anything. The energy crisis brought about energy codes, and the resulting mold & toxics problems brought about ventilation codes.
All these laws have a common thread: they tend to be "one size fits all" solutions. Although many codes allow for the possibility of unique solutions that still meet the underlying safety or performance concern, in practice it is often difficult to get those past unless the building inspector is open to those possibilities. As more people use alternative techniques and materials, inspectors become more familiar and hence more open to allowing them. As we will see, the very nature of Green Building is to design with basic principles in mind rather than using a "one size fits all" approach.
The one place where codes cross with green building is when the affect aesthetics, and they are safety measures the average homeowner treats with the same respect as a 55mph speed limit on the highway (ie very little). The newer, very stringent requirement for handrails and guardrail come to mind, but there are certainly others.3
As energy and climate change become prevalent political issues, it is likely that energy codes will become more common. While specifying minimum levels of insulation, minimal performance standards for windows and appliances help push industries toward efficiency, attempts to regulate consumer behavior, for example by requiring CFL lights, and motion detector switches may result in a negative consumer acceptance of green building, and smaller than projected energy savings. While heating & cooling energy is mostly a function of insulation levels, electric usage is a largely a function of consumer choice: you can still leave your 52" plasma TV on all day, put in a hot tub and leaving the cover off, and a whole plethora of other electrical hogs.1
Green Rating Systems
A parallel effort to set a standard for Green Building has been created by a number of organizations: in the United States principally by local home building organizations (all affiliated with the National Association of Home Builders) and by The US Green Building Council, a non-profit organization. In all cases there is an attempt to quantify how green a building actually is. The simplest, and currently the most common method for home building is to use a checklist of green features and count how many of them are applied, giving various points to each item, and an overall score based on the total number of points. For example in the Seattle Master Builder, Built-Green program, one can achieve a rating of 1 to 5 star. In the USGBC LEED for homes rating system, the award levels are Silver, Gold and Platinum.
The more complex methods are performance based, but to date most of the performance requirements are all via modeling, not actual performance. Since performance can be very hard to qualify, even these methods award points for the use of specific techniques.
To give an example: in the prescriptive (or checklist) approach, a builder might say "insulated beyond code", "used advance framing", "used energy-star appliances" etc, while in the performance based approach, the builder must say exactly how much energy is expected to be saved versus standard building.2
While all these rules and rating systems are a step in the right direction, Green Building's general principal are to start first principles, and because it is so hard to determine performance until the building actually exists and has operated for a number of years. Because designers experienced with the rating systems can go on a points chase while somewhat ignoring those first principles, and because design & reality just don't always match, there is sometimes a significant gap between predicted performance and actual.
Notes
1: In particular, California's Title 24 is a totally bogus attempt to regulate energy use. People put in the code compliant lighting, then throw it out once the inspector is gone. My general problem with this approach is that its "all stick, and no carrot". You get no credit for PV, nor do they give you a "energy hero" discount is you use almost none. All they care is that you put in pin CFLs (so you can't change to incandescent), and motion sensors, cause they're sure you're too dumb to turn off the light yourself. No doubt, the diehard light users will just buy table lamps and leave them on. I agree that lighting can be a major energy user, but its all behavior. I'd further argue that the "CFLs" everywhere is not the best environmental choice: put CFLs in the fixtures that are on the most, and incandescent in the rest of them.
A more detailed look at this is on the lighting and electric pages.
Under Title 24, even if you build superinsulated walls, you have to fill out this heat loss chart to show you're code compliant: there is no "I'm trying to build a near zero energy house, leave me alone because I'm way beyond your code" path. There appears to be an entire industry of people who fill out Title 24 paperwork.
I'm not opposed to energy codes, but from what I've seen, Title 24 is a lousy one.
2: in practice, there is often a big gap between projected energy use and actual energy use because behavior is such a large part of energy use, but then it isn't generally fair to penalize the design team for bad behavior on the occupants part (although it sometimes is).
3. I would love to know how much stuff gets thrown out within a year of the building inspector leaving. A cable TV guy once told me he went around to jobsites after people moved in and collected all sorts of stuff (this is California, which potentially leads the nation in stupid building codes.)