Residential energy codes have evolved rapidly over the last two decades. The origin of many of our current energy codes can be traced back to the Model Energy Code (MEC), which was first introduced in 1992. The MEC eventually evolved into the International Energy Conservation Code (IECC).
In jurisdictions that have adopted the International family of codes, residential builders can usually use the IECC to fulfill energy code requirements. But most home builders choose instead to follow the simpler energy requirements found in the International Residential Code (IRC). Confusingly, IRC energy requirements are similar but not always identical to requirements found in the IECC.
The 2004 Supplement to the IECC included radical revisions to the existing energy code. These revisions were designed to simplify the code, in hopes that a simpler code would lead to better compliance by builders and easier enforcement by building officials. These 2004 revisions were designed to be “stringency neutral” — that is, to result in homes that were neither more nor less efficient than homes built to earlier versions of the code.
The 2004 revisions were fully implemented in the 2006 versions of the IECC and IRC. The latest version of the codes — the 2009 IECC and IRC — include revisions designed to increase energy code stringency. (For more information on changes adopted into the 2009 codes, see Exceeding the Energy Code.)
The window-to-wall ratio
In pre-2004 versions of the IECC, builders were required to calculate the ratio between a home’s window area and its solid-wall area; this ratio was usually called the window-to-wall ratio (WWR). No matter which compliance path a builder chose — the prescriptive path, the component trade-off path, or the performance path — there was no escaping the requirement to calculate the WWR. Some builders grumbled at the need to make this calculation.
Homes with a low WWR usually use less energy than homes with a high WWR. For builders following the simplest (prescriptive) path, a WWR of 15% marked an important dividing line. Under older versions of the code, homes with a WWR of 15% or less were permitted to follow R-value requirements in one table, while homes with a WWR over 15% needed to follow stricter R-value requirements in a different table.
In spite of the fact that WWR calculations used to be code-required, they were often flouted and were never strictly enforced. During site inspections, building inspectors rarely brought along a home’s energy calculation report; furthermore, inspectors almost never measured window sizes to verify compliance.
The code is radically simplified
The 2004 code changes (fully implemented in the 2006 International codes) were promoted by the U.S. Department of Energy in response to critics who complained of code complexity. To simplify the code, the number of climate zones was reduced from 19 to 8. All references to heating degree days and window-to-wall ratio calculations were eliminated.
As a result of these changes, the new code no longer penalizes a house with a large WWR — as long as the builder follows the prescriptive path. Although some builders have welcomed the freedom from calculating a home’s WWR, other builders — those who build simple homes with low WWRs — began to grumble. With the earlier code, low-WWR houses received a credit that could be used as a trade-off for lower insulation levels in 2×4 walls; once WWR limits were eliminated, this credit vanished.
The 2006 IECC included several new mandatory provisions, including a requirement (403.2.2) for R-8 insulation on ducts located outside the thermal envelope, and a requirement (401.3) for posting a “panel certificate.” This document — which must be permanently affixed to the electrical distribution panel — must list the home’s insulation R-values, window U-factors, window SHGC values, water-heater efficiency, and furnace or boiler efficiency.
Three possible paths
For years, energy codes have offered three compliance paths: the prescriptive path, the component trade-off path, and the performance path. The latest versions of the International codes retain all three paths.
The prescriptive path is the simplest — though not necessarily most cost-effective — way for builders to meet energy-code requirements. Prescriptive-code requirements are shown in a table (Table N1102.1 in the 2009 IRC) that specifies minimum R-values, maximum U-factors, and maximum SHGC values; these prescribed values vary by climate zone.
The prescriptive table allows lower R-values in walls with high thermal mass — ICF walls, for example — than in wood-frame walls.
The “Total UA” alternative
In the 2009 IRC, the component trade-off path is known as “the Total UA alternative”; it is found in section N1102.1.3. Builders who choose the Total UA Alternative path can choose insulation thickness and window U-factors that deviate from those in the prescriptive table, as long as the total building thermal envelope UA (the sum of each assembly U-factor times each relevant area) is not more than the total UA resulting from using the U-factors in the prescriptive table.
The easiest way to follow a component trade-off or total-UA path is to use computer software — for example, a free program called REScheck. REScheck was developed by the U.S. Department of Energy, and can be downloaded at no charge from the DOE’s EnergyCodes Web site.
In most jurisdictions, a building permit will not be issued until the builder has submitted documentation — such as a REScheck report — showing that the design complies with the local energy code. Energy code documents are prepared by a range of service providers, including builders, engineers, architects, energy consultants, lumberyards, and heating contractors.
Although REScheck reports are routinely prepared by builders in many areas, a few jurisdictions — including some New Jersey municipalities — require REScheck calculations to be submitted by a licensed engineer.
California’s energy code, called Title 24, is unique. Because of the code’s complexity, California builders usually demonstrate code compliance by hiring an energy consultant familiar with the use of Title 24 software.
The performance path
The performance path (also known as “the simulated performance alternative”) is found in Section 405 of the 2009 IECC. Builders following this path must show that a proposed house design has an annual energy budget (in dollars) less than or equal to that of a similar house (known as the “standard reference design”) that complies with the code’s prescriptive requirements.
Simulated performance alternative calculations are usually performed by an energy consultant, HERS rater, architect, or engineer. The calculations are made using a software program like REM/Rate. This path to code compliance is the only way a builder can get full credit for certain energy-efficiency features that are not otherwise required by code — for example, window orientation optimized for passive solar heating or an unusually tight thermal envelope.
Code compliance varies
Over the past decade, several studies have documented the fact that in many areas of the country, energy code provisions were largely unenforced. For example, a 2001 study in Fort Collins, Colo., investigated duct tightness in new homes. In spite of a local code provision that required ducts to be “substantially airtight,” performance testing in new homes revealed that HVAC systems had duct leakage averaging 75% of system airflow.
Similarly, a 2001 study of 186 new Massachusetts homes found that only 46% of the homes met minimum code requirements for UA (building envelope U-factor) and only 19 percent met code duct-sealing requirements.
Some states, including Vermont, adopted an energy code years ago, but never established any type of code enforcement mechanism. To this day, most Vermont jurisdictions have no building inspectors. In essence, the Vermont energy code is entirely voluntary.
Some builders see lax code enforcement as a blessing. The trouble with uneven enforcement, however — in addition to the obvious point that energy waste contributes to global climate change — is that a builder can never be sure when a new building official will begin enforcing
Meanwhile, out in the field…
I recently spoke with Mike DeWein, the technical director of the Building Codes Assistance Project. DeWein noted that some energy experts were uneasy when window-to-wall ratio restrictions were eliminated from the code. “We don’t know what window-to-wall ratios are now,” DeWein told me. “According to the window industry, in most places new homes don’t go over 16% or 18%. But some states looked into it and came up with data that showed that there are lots of homes with glazing ratios over 20% — for example, in Texas, where lots of McMansions were being built during the boom.”
Like most energy code experts, DeWein bemoans the fact that most states show little interest in improving code compliance rates or improving code enforcement. “Are people complying with the energy code?” asked DeWein rhetorically. “We just don’t know. We’re starting to study that now. Some states are engaged in a DOE pilot study to look at energy code compliance rates — others are undertaking compliance baseline studies on their own. We know there are many places that have adopted the code but that don’t enforce it.”
According to DeWein, most enforcement efforts are weak. “Energy codes can have such a greater impact than the voluntary programs, but it takes fortitude to do them,” he said. “It’s not like handing out incentives — it’s regulation, and everyone hates regulation.”
The states eagerly accepted Recovery Act funds
In an attempt to improve code compliance and enforcement, the Obama administration awarded individual states millions of dollars to fund energy code improvements. “We know that some states have adopted the code but have done nothing to ensure implementation,” said DeWein. “There were great amounts of money in the Recovery Act for energy efficiency — funds that were handed out to all the states. They all took that money. While there wasn’t any great set of teeth to the Recovery Act preconditions, it was understood that the states were supposed to adopt the 2009 code and meet compliance goals by 2017.
“But many of those states earmarked very little of that money for energy code implementation. Some jurisdictions don’t want to do the regulatory stuff, so they just kind of blew it off. There are a bunch of states that are making a good effort, including most of the Northeastern and Northwestern states. About half the states have adopted or are on their way to adopting the 2009 code. But we have a lot more states that need to invest in both adoption and implementation.”
I asked DeWein, “If you were emperor, how would you improve code enforcement efforts?” DeWein responded, “If it were up to me, I would be looking for building performance professionals to be implementing the code. One model might be to utilize third-party raters. It could be similar to the way electrical inspectors work in some jurisdictions; electrical inspectors are often independent third-party players. So why couldn’t we use building performance professionals to act as inspectors?”
A portion of this article appeared in the Journal of Light Construction.
Last week’s blog: “The Return of the Energy Quiz.”