May 2017

Next Generation Green Building Codes: Modeled Performance


Katherine Mortimer


In 2009 the City of Santa Fe adopted a green building code for new single-family residences. The code addressed building energy use, water conservation, greenhouse gases embedded in building materials, indoor air quality, lot design and homeowner education. Recently, the city, in consultation with the local building community, adopted a major change in the code focused more specifically on energy, water and indoor air quality, using three performance standards. 


The big (good) news is…there’s no more checklist! Most green building programs use a checklist of items in a range of topic areas. The process of collecting cut sheets and verifying percentages of recycled material and a host of other verification activities takes an inordinate amount of time, which equates to money.


Santa Fe’s 2009 checklist format had six topic areas with minimum point requirements in each. These had to be verified at least twice—once to get a building permit and again during or at the end of construction. However, one component of the program was different. These residences also needed to get a specific Home Energy Rating Score (HERS®) index. At the time it was a score of 70, which was about 30 percent more energy-conserving than the 2006 International Residential Code. This is an example of a performance requirement. It didn’t matter how you got to that number. People would increase the building insulation, purchase more efficiency equipment such as heating, air conditioning, water heating and dishwashers, use passive solar design and/or install photovoltaic solar panels. Builders and designers reported that they appreciated the flexibility that this performance requirement provided. 


At the same time the green code was adopted in 2009 the city also adopted a resolution to improve building energy-efficiency over time to meet the 2030 Challenge. The 2030 Challenge is that all new buildings be carbon-neutral by the year 2030. That means increasing the efficiency by several percentage points every few years. Unfortunately, the economic downturn severely affected the home-building industry, and when the time came for increasing the requirement, no one wanted to make building in Santa Fe any more expensive. So we waited.


In the meantime, a group of local water conservation specialists, builders, designers and energy raters saw an opportunity to develop a tool to determine a home’s water efficiency, as HERS® did for energy. This tool would include both indoor and outdoor water to get a picture of the total water consumption. This team found a national non-profit green building organization that saw the potential of this new tool and had the resources to develop it. The Water Efficiency Rating Score or WERS® tool came into being, allowing the city to consider moving away from the checklist-based program to one that is fully performance-based. 


Performance-based means that the building is designed to reduce water and energy use, just as a hybrid car allows for better gas mileage. That doesn’t mean that every house will have specific and predictable water and energy bills. Just like a hybrid car, if you drive it in a way to maximize your gas efficiency, you can get even better gas mileage than the car’s rating. Similarly, if it is driven with frequent quick speeding up and slowing down, the car will get worse gas mileage than the sticker says. It is the same for water and energy use in a home. Two people might live in a 3-bedroom home and use less water than predicted, while another family in an identical home with two adults and two teenagers involved in sports, who shower frequently and have lots of laundry, would likely use more water and energy. The scores measure the predicted water and energy use of a “typical” number of occupants based on the number of bedrooms, using national water- and energy-use data, adjusted for climate.


The importance of including water as a key resource to conserve is not just because of our location in the arid Southwest. It takes a lot of water to produce coal and nuclear energy, and it takes a lot of energy to extract, clean and deliver water and then to move and treat sewage. This water-energy nexus becomes more important as other energy conservation measures are achieved, and the amount of energy “embodied” in our tap water becomes a bigger piece of a building’s greenhouse gas emissions.


As the number of building permits for new homes started to return to normal levels, there was renewed interest in improving required building energy efficiency and adding a water performance requirement. The checklist had included an air-ventilation performance requirement as well. Under the new performance-based code update, HERS® measures a home’s expected energy use; WERS® measures a home’s expected water use; and a specific amount of ventilation based on the number of bedrooms and the size of the home ensures healthy indoor air quality. A few items from the checklist that emerged as universal best practices were added as requirements, and the code became a performance code. Get the expected “mileage” in water, energy and air exchanges and include a few specific requirements, and throw away the checklist.


There are some new costs such as contracting for a WERS® professional to show that the home meets the required score and then verifying the installation and flowrate of water equipment.  However those costs are more than offset by not having to complete the checklist and demonstrate that the building will make the points in all six sections. The city has now developed a homeowner’s manual rather than having developers create their own. Builders only need to download and print the most recent version and add a few items such as a diagram showing the location of major utility shutoffs and the manuals for major equipment and appliances. Even with increasing the required energy efficiency, analysis shows that the overall cost of compliance will have a net cost savings in almost all cases.


By using a performance model, the city hopes to be able to add commercial buildings to the green code. Existing models available for commercial buildings are expensive to comply with and expensive for the city to administer. Performance modeling of commercial buildings would mean it would be just as easy to ensure water-and energy-efficiency and indoor air quality in commercial buildings as in residential. Stay tuned to see this further development of the green code once the WERS® tool is expanded to model commercial buildings.


Katherine Mortimer is the Sustainable Land Use supervisor for the City of Santa Fe. She facilitated the development of green codes for new residences, residential additions and remodels, and the recent update to a performance code the city hopes to use as a model for multi-family and commercial buildings.




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