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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.

Mandatory Requirements

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."

Big Changes to the IECC

Besides being 150 pages shorter than the previous edition, the 2006 IECC incorporates radical code revisions. The changes were promoted by the U.S. Department of Energy in response to critics who complained of code complexity.

The rewriting of the IECC was intended to be "stringency neutral" — that is, to result in houses that are just as efficient as houses built to earlier versions of the code.

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Among the most important changes to the 2006 IECC are the following:

• The number of climate zones has been reduced from 19 to eight, and all references to heating degree days have been eliminated.

• All references to the WWR have been eliminated.

With the elimination of window-to-wall area restrictions, the 2006 IECC no longer penalizes a house with a large WWR. Although builders will probably welcome the chance to jettison WWR calculations, anyone accustomed to building houses with few windows may be surprised to learn that some house designs that formerly met code may no longer comply. The reason is that the 2006 IECC no longer allows builders to get credit for a low WWR as a trade-off for lower insulation levels in 2x4 walls.

"The intent of the code was never to create caves with no windows," says DeWein. "The intent was to try to do a static heat-loss analysis and to compare the home with some baseline. With the older versions of the IECC, when you had designs with low window areas, they scored a little better overall. With the new code, that's no longer the case."

Like the earlier versions of the code, the 2006 IECC has three compliance paths. Builders who choose the prescriptive path must follow the requirements of Table 402.1, which specifies the maximum window U-factor, maximum skylight U-factor, maximum window SHGC, and minimum R-values for ceilings, walls, floors, basement walls, crawlspace walls, and slabs. These specifications vary by climate zone. Table 402.1 allows lower R-values in walls with high thermal mass — ICF walls, for example — than in wood-frame walls.

Builders who choose the component trade-off path (which the 2006 IECC calls "the U-factor alternative") must follow the requirements of Section 402.1.2. The easiest way to comply with this path is to use REScheck software.

The requirements for the systems analysis path (which the 2006 IECC calls "the simulated performance alternative") can be found in Section 404 of the 2006 IECC. While earlier versions of the IECC base systems analysis comparisons on a home's annual energy budget as measured in Btus or kilowatt-hours, the 2006 IECC requires that the comparison be based on the dollar cost of the energy used.

The 2006 IECC includes 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.

The latest version of REScheck includes a new clickable button that automatically generates and prints a panel certificate.

Here are a few more noteworthy provisions of the 2006 IECC:

• The code waives SHGC requirements for windows in the special marine zone along the Pacific coast, where cooling loads (and therefore solar-gain concerns) are low.

• The code (402.2.1) allows builders who use raised-heel trusses to reduce the thickness of attic insulation, as long as the insulation covers wall plates at the eaves.

• The code (402.2.2) allows builders in climate zones where R-38 ceiling insulation is normally required to install R-30 insulation in a cathedral ceiling if that's all that will fit, as long as the area of the cathedral ceiling doesn't exceed 500 square feet.

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.

Energy-Code Resources

Every builder needs to know what documents are required by the local building official to demonstrate compliance with local energy codes. A wealth of resources is available to builders looking to learn more, including the following:

• The local code authority

• The Web site of the state energy office

• A useful Web page maintained by the Pacific Northwest National Laboratory at resourcecenter.pnl.gov

• The Web site of the Building Codes Assistance Project at www.bcap-energy.org

• Model residential energy code books available from the International Code Council at www.iccsafe.org

• The Code Notes Web page maintained by the DOE's Building Energy Codes Program at www.energycodes.gov/support/code_notes.stm

• Free online training (Webcasts) for REScheck users available through www.energycodes.gov

• A very useful book, Field Guide to Residential Construction, produced by the Conservation Services Group; state-specific versions of the book (available for Connecticut, Idaho, Maryland, Massachusetts, Montana, New Hampshire, New Jersey, New York, Oregon, Rhode Island, Vermont, and Washington) are distributed through each state's Energy Star Homes program.

Martin Holladayis the editor of Energy Design Update.