In 2010, we wrote:
"The updated California energy code is changing the insulation and plaster systems being used throughout the state."
We said it then and we have to now say it again, and this time the impact of the 2013 California Energy Code standards will be much more significant than the last cycle. This is because the new code requires significant upgrades in the insulation of wall systems. For the past few years, residential standards for wall systems in much of the most populated areas of the State were status-quo, and commercial standards were done by measuring the effective insulation value of the entire wall system, taking into account thermal transfer through framing and windows. This overall approach to wall insulation now comes to residential construction with the start of the 2013 standards in July, 2014. This represents a paradigm shift in how exterior walls of residential structures will be built in the State
Climate Zones played a big role in the residential wall requirements in the past edition of the energy code; not so now. All climate zones now require an overall wall U-factor of 0.065. That translates into an effective R-value of about 15, taking into account the leakage through studs called thermal bridging. To comply, many new homes will be built with continuous insulation, a method in which foam board is installed outside of the framing in a continuous sheet, with the exterior cladding installed over it.
It is important to understand that tradeoffs between systems are allowed. As long as the house will use the same amount of energy as the specified designs, you can trade off insulation against windows, HVAC systems, etc.
How Are Builders Complying?
In order to comply with some of the stricter requirements under Title 24, continuous foam insulation (CI) is becoming more common. The use of foam panels applied outside of the studs necessitates the use of a plaster system specifically designed for use with foam panels. Commonly known as “one coat stucco systems” or EIFS, these plaster systems can achieve insulation in the wall system that is equivalent to Title 24 requirements or better. For instance, a home in Palm Springs could choose to use R-21 insulation between 2x6 wood studs, spaced 24 inches on center, OR R-13 batts between 2x4 wood studs with 1-1/2 inches of foam board and an insulated plaster system. See Table 1 for more details on residential CI systems.
In commercial buildings using metal framing, the reasons to use CI systems are even more compelling. Because metal studs permit the transfer of more energy out of the building, their performance is improved more than wood-framed buildings by the use of foam insulation outside the studs. It would be difficult to comply with Title 24 building with metal studs without foam insulation in many climate zones, unless other significant energy upgrades were made in other parts of the building. For instance, building with a CI plaster system in San Francisco, Los Angeles, or San Diego, a builder can achieve Title 24 compliance with 1-1/2” of CI foam over 4” metal studs and R-11 batt insulation. See Table 2 for details on code-compliant CI systems for commercial structures.
Metal-framed hotels and high-rise residential have the same standards throughout the state. A U-factor of 0.105 is required, which can be met with 1 inch of CI foam over 4” metal studs with R-13 batts. Over wood framing, half the state allows a U-factor of 0.059, which can be met with 2x6 studs, R-19 batts, and R-4 CI. The most extreme zones of the state require U=0.042, which requires 2x8 studs. See Table 3 for details for use with hotels and high-rise residential projects.