The Systems Analysis Path
Sophisticated energy modeling software is needed for the systems analysis path. Depending on the state, the systems analysis path may be called the systems performance path, the simulated performance alternative, or whole-house performance analysis. It's found in Chapter 4 of pre-2004 versions of the IECC. In general, builders following this path must show that a proposed house design has an annual energy budget less than or equal to a similar house that complies with the code's prescriptive requirements.
While REScheck is perfectly adapted to calculating the effects of component trade-offs, it cannot be used for the systems analysis path. Builders following the systems analysis path need to use a program like DOE-2 or REM/Rate, the software used by consultants who rate a home using the Home Energy Rating System (HERS) index. Whereas the REScheck program has no way for a builder to input a home's air infiltration rate, REM/Rate does — so that a very tight home can obtain credit for its superior performance compared with a typical, somewhat leaky home.
If a builder follows the systems analysis path for code compliance using an air-infiltration rate that is lower than the code-specified default value, the code stipulates that a blower-door test must be performed to verify that the home meets its tightness goal. In theory, a builder who cannot provide blower-door results under these circumstances can be denied a certificate of occupancy.
Systems analyses are usually performed by an energy consultant, HERS rater, architect, or engineer. A systems analysis is the only way a builder can get full credit for certain energy-efficiency features that are not otherwise required by code — window orientation optimized for passive solar heating, for example, or a sealed and tested duct system.
Following the systems analysis path makes sense for homes that have unusual design or energy-efficiency features. Because the systems analysis path usually requires the assistance of an energy consultant, it is rarely used for residential construction.
In addition to offering three compliance paths, residential energy codes impose additional mandatory requirements. For example, pre-2004 versions of the IECC require attics to be equipped with permanent insulation depth markers.
Mandatory requirements also vary from state to state; for instance, Washington state requires all homes, regardless of which path is used for code compliance, to be equipped with a whole-house ventilation system and equipment to provide combustion air for solid-fuel appliances.
Getting Your Permit
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.
Many builders are happy to hand off responsibility for code-compliance paperwork. "In Wisconsin, the overwhelming number of REScheck reports are done by the lumberyard or the heating contractor," reports Nagan.
What About Airtightness?
Since many attributes of home performance are not regulated by code, complying with the energy code, though necessary, is not sufficient to guarantee that a house will be energy-efficient. For example, the prescriptive and component trade-off paths do not directly address a home's air-leakage rate. As Nagan notes, "REScheck can perform trade-offs between heating equipment and insulation levels, but REScheck knows nothing about infiltration."
In some countries, such as Sweden, a new home must pass a blower-door test before it can be issued an occupancy permit. U.S. codes, however, show no sign of following Sweden's lead. "The 2006 IECC is better at calling out how one deals with air leakage and duct sealing," notes DeWein. "But there is still no performance metric for it, unless you go to the full performance methodology."
The 2006 IECC requires submitted plans to indicate air sealing details (104.2); it also specifies that "the building thermal envelope shall be durably sealed to limit infiltration" (402.4.1). Some state codes, including the Minnesota, New York, and Oregon residential energy codes, have similar mandatory requirements intended to improve the airtightness of a home's envelope. Oregon's provisions are subject to interpretation by local building officials: "All exterior joints around windows, around door frames, between wall cavities and window or door frames, between wall and foundation, between wall and roof, and other openings in the exterior envelope shall be sealed in a manner approved by the building official."
A house that complies with the energy code does not necessarily include all cost-effective efficiency measures.
"Most Wisconsin builders install one inch of foam on the exterior of their basement walls," says Nagan. "When we do our REM/Rate action reports to evaluate a house for an Energy Star builder, overwhelmingly the reports show that the foundation is the largest contributor to the heating cost. Even Energy Star builders are using just one inch of foam, so these buildings still have a very weak link. These homes could be cost-effectively upgraded, with no more labor, just by going from one inch of foam to two."
Code Compliance Varies
Several studies have documented the fact that in many areas of the country, energy code provisions remain 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 percent of system airflow.
Similarly, a 2001 study of 186 new Massachusetts homes found that only 46 percent of the homes met minimum code requirements for UA (building envelope U-factor), and only 19 percent met code duct-sealing requirements.
Building officials rarely bring along a home's REScheck report during site inspections. Although all residential energy codes except the 2006 IECC impose window-area limits, "there is not a single jurisdiction in the country that goes out and measures window areas on site," says Craig Conner, a former engineer at the Pacific Northwest National Laboratory in Richland, Wash.
Some states, including Vermont, have a mandatory energy code but no system of enforcement. "In Vermont, compliance with the energy code requires filing a copy of the documentation report with the local town clerk," says Richard Faesy, a senior energy analyst for Vermont Energy Investment Corp. in Burlington. "As far as I know, fewer than 10 percent of new houses are in compliance with the code. There's no enforcement infrastructure."
Many builders see lax code enforcement as a blessing. The trouble with uneven enforcement, however, is that a builder can never be sure when a new building official will begin enforcing long-ignored regulations. Builders intent on following the code as written should be aware of the following rarely enforced provisions:
• Some codes (for example, in Massachusetts and California) include duct-tightness requirements.
• Many codes (IECC 102.2, for instance) include a provision requiring all materials, systems, and equipment to be installed according to manufacturers' installation instructions. According to this provision, fiberglass batt insulation must be installed without voids or compression. Moreover, housewrap must be carefully lapped at horizontal seams, and some brands of housewrap must have taped seams.
• Many energy codes (such as IECC 803.2.1.1) require "right sizing" of hvac equipment; according to this requirement, oversized furnaces, boilers, and air conditioners violate the code.Martin Holladayis the editor of Energy Design Update.